The Under Engineered Ham

G5RV JUNIOR

2025-06-02T08:33:00.000-07:00

I've been away for a long time. Haven't run across much that I thought was worth posting until now.

I was running EZNEC simulation on a G5RV Junior yesterday and ran into the following. I simulated 40 through 10 meters on a friend's proposed installation. The plan was to put the center at 24 feet and the ends at 10 feet. The following graph shows the problem with 10 meters with that installation.

Definitely not a good DX antenna and 28 MHZ is too high frequency for NVIS operation. So I changed the simulation so the ends of the antenna are at 20 feet.

Certainly a more acceptable installation for 28 MHz.

All of the lower frequencies bands provide a more acceptable patterns even with the ends at 10 feet and moving the ends up to 20 feet made little difference to the lower bands.

Turns out even raising the entire antenna by 5 feet produces an acceptable pattern.

Just thought you'd find this interesting and hopefully useful.

UPDATE TO FEED LINE CHOKE FROM COAX

2025-05-13T10:13:00.000-07:00

I recently received an email from a reader asking to what the Length in the following chart referred.

Admittedly at first I was at a loss to answer his question. It refers to the height of the coil when using RG-174. Poor choice of a word on my part. Length should be replaced with height throughout the paper.

The following chart gives a list of coaxial line chokes for various ham bands.

Turns Diameter* Height* Coax type Band Coverage

13 8 3.25 RG-174 160 meters only

RG-58

RG-8x

9 9 3 RG-174 80 meters only

RG-58

RG-8x

8 6 2 RG-174 40 meters only

RG-58

RG-8x

9 4 2.25 RG-174 40 – 30 meters

RG-58

RG-8x

8 4 2 RG-174 30 – 20 meters

RG-58

RG-8x

5 5 2 RG-174 20 - 15 meters

RG-58

RG-8x

6 4 2 RG-174 17 - 10 meters

RG-58

RG-8x

4 3 1 RG-174 6 meters only

RG-58

RG-8x

* - Height and Diameter are in inches.

Thanks for pointing it out Tim.

Thirteen of RG-174 is 1.43 inches high. You will need to space the turns to achieve a coil height of 3.25 inches.

TIGER TAIL AND YOUR HT

2023-03-12T17:05:00.000-07:00

It's been a while since I've added anything new. I've been busy hamming and doing very little in antenna design and test. Most recently I've done some preliminary testing of tiger tails. A tiger tail is a quarter wave length of wire attached to the ground side of the antenna connection of a handy talky. It is left to hang off the radio and provides the other half or ground half of the antenna.

I have yet to test my findings On The Air (OTA). We've had a rather extreme winter here in Utah as have many other parts of the country. So OTA testing is waiting for better weather. However, here's my findings so far.

My first encounter with a tiger tail a few years back was to attach one to my Icom T7h with the factory provided rubber ducky antenna. The result were not good. I had a friend, now SK, who lived about 2 miles from my house run field strength tests. He turned his 2 meter beam on my signal until his beam found the null in my signal. This was without the tiger tail. He then used his rf gain and built in attenuator to get my signal to S9 his receiver. I then added the tiger tail to the rubber ducky that came with my HT. My signal dropped to just under S7. That is about 6 dB or the same as cutting the signal in half and cutting the remaining signal in half again. Based on that test I decided tiger tails were not the helpful device some people seemed to think.

A bit about the latest tests I have run. I have three "rubber ducky" antenna now and three quarter wave whips for 2 meters all of different design. I used my nanoVNA for the initial impedance/SWR tests.

All three rubber duckies suffered from considerable impedance shift and increase in SWR beyond 2:1 over the upper part of the band. The resonant point was shifted downward by the addition of the tiger tail.

However, adding the tiger tail to all three quarter wave whips did little to shift the impedance. The band width of all three antennas did get slightly narrower but not so much that the SWR reach 2:1 anywhere on the band.

I am looking forward to OTA testing when the weather improves. Hopefully, adding the tiger tail will improve the signal strength. When I get some OTA test results, I'll share them with you.

Update: 51 Foot Non-Resonant RV Antenna

2020-11-16T08:19:00.000-08:00

I have since obtained a second 30 foot pushup fiberglass mast from Jackite.com that I now use at the front of the trailer. I have now gone to 72 feet of #16 wire so that I can work 80 meters. The antenna now forms an inverted U shape. Every thing else remains the same.

The real test of this will come in January during Winter Field Day. I'll post follow-up OTA results after that.

51 Foot Non-Resonant RV Antenna

2020-02-09T11:14:00.001-08:00

I own a Jayco 23 foot camp trailer. I often go to RV camp grounds and I like to get in some hamming away from my home QTH. I've always been concerned about hazards to the other campers such as guy wires or wire antennas that have fallen down. As a result I been searching for alternatives that minimize these potential hazards. Some of my RV'ing friends use Buddy Poles others use mobile whips mounted on their RV's. The most common method it to permanently mount a mobile mount on the ladder used to access the top of the RV. Once their camp is set up they attach the mobile whip and feed line to the mount.

My trailer does not have a ladder. So my solution was to put a second spare tire mount (available at Harbor Freight) on the rear bumper of the trailer. I "rigged up" a couple of eye bolts and a locking hitch pin to hold a mast. A short piece of PVC protects the fiberglass from damage when it moves because of wind. See Picture 1 and 2 below. I prefer a Jackite 30 foot fiber glass telescoping pole available at jackite.com or amazon.com. I use a Jackite 20 pole strapped to the gas bottle cover in the front to hold the far end of the antenna. That way everything is over the trailer. These poles are not fishing poles with the very flexible top section. These poles are designed for wind socks and flags. The top section is not hollow tube but rather sturdy solid rod.

The antenna is 51 feet of #22 AWG stranded wire used in aircraft construction. This is just wire I had in the "junk garage". Yes my junk box is one side of a three car garage. The only thing I'd recommend on the wire is that you use something quite flexible. I pull the wire up to the top of the 30 foot pole on a halyard. The far end goes to the 20 foot pole to make an inverted L with the vertical leg 30 feet and the horizontal led 21 feet running downward at about 30 degrees. This downward angle is of little significance in the antenna's performance. I use a light chalk line type cord throughout. The horizontal leg does not reach the 20 foot pole so I use the same cord to make up the need length to reach the wire and then down to pole.

Picture 1

Picture 2

I wound a 9 turn unun on 2 1/2 inch PVC pipe with about 1/2 inch spacing. The wire is bare #14 AWG. I used hot glue strips at interval 1/4 the way around to hold the wire in place. See the Picture 3 below. I tapped the unun as shown in the table below.

Picture 3

1.75	7.25	4.14	:1	17.16	:1	858
2.00	7.00	3.50	:1	12.25	:1	612
2.25	6.75	3.00	:1	9.00	:1	450
3.00	6.00	2.00	:1	4.00	:1	200
3.50	5.50	1.57	:1	2.47	:1	123
4.00	5.00	1.25	:1	1.56	:1	78
4.50	4.50	1.00	:1	1.00	:1	50

I used four large mix 31 snap on ferrite beads distributed around a two turn 6 inch coil of the feed line about a foot away from the unun to suppress RF on the feed line getting into my RV. See Picture 4 below.

Picture 4

I ran this setup for nearly a month this summer while out and about with good results. I did not use that data because I felt it was better to use the Winter Field Day data. The Winter Field Day data is the same mode and power throughout. The resultant date will be a better representation of the antenna's performance and not a function of applied power or operating mode.

Antenna design model

The grounding scheme is a closed loop around the perimeter of the trailer. It is a 68 foot long loop made of 2 inch wide aluminum/mylar tape. ("Mutual Industries 17774-25-2000 Polyethylene Underground Water Line Detectable Marking Tape, 1000' Length x 2" Width, Blue" available at Amazon, about $30 last I checked). This works like a non-resonant counterpoise or ground mat. It just provides capacitance to ground. That is the wires you see in the model labeled 4, 5, 6, and 7. I loop it around the trailer to keep people from tripping on it.

The "on the air" performance for the antenna is documented below with data from my Winter Field Day log. I was running 25 Watts on PSK31 for the entire time using battery power. The radio was my IC-7300. I used my LDG Z-11PRO tuner with 20 feet of RG8x feed line into the trailer. The tuner in the 7300 does not handle wide range of impedance presented by the antenna.*

------------------------------------------------------------------------------------------------------------------------

Winter Field Day Log Data

Call UTC Freq    Distance
------ ----- -----   --------
Begin 01/25/20
W7D 19:15 7.071 671.1
KN4FRG 19:43 14.070 1076.7
N5OAK 19:51 14.071 1092.9
W0ARC 19:56 14.070 1057.8
KC5LVW 20:02 14.070 1077.3
KD5ILA 20:10 14.070 1042.0
KI4ITI 20:30 14.071 1444.9
K9BY 20:52 14.070 1190.9
N4MZ 21:22 14.070 1541.8
N4ZC 21:25 14.071 1728.8
W5AWL 21:52 7.071 1014.0
KB9REV 22:04 7.071 1251.8
W7A 22:06 7.070 707.2
NV7AV 22:15 7.071 392.0
WA5WRL 22:27 7.071 1022.0
W0BLK 22:30 7.071 493.4
K7SI 22:46 7.072 285.9
W4CVY 22:56 7.071 1606.6
WB6AGE 22:58 7.071 662.0
K5LRK 23:02 7.071 1001.4
KC8QDP 23:09 7.071 1582.5
K5OQ 23:47 7.071 1133.6
N7YIQ 23:51 7.070 415.7
W0IZ 23:56 7.071 266.8
Begin 01/26/20
AD0ND 00:02 7.071 804.3
W7GBU 00:07 7.072 514.8
KD5ILA 00:16 7.070 1042.0
W9UUU 00:22 7.072 1301.1
W4GR 00:26 7.070 1603.4
KC3FL 00:31 7.071 1872.5
W3GQ 00:34 7.071 1719.7
NV1O 00:38 7.070 531.7
K6EI 00:44 7.071 589.8
WD6RAT 01:02 7.070 556.7
W7PIG 01:07 7.071 317.8
N4MZ 01:49 7.070 1541.8
W2OW 01:51 7.071 1851.3
K5IJ 01:53 7.071 1477.5
W2SO 02:01 7.071    1711.2
W8VVL 02:14 7.071    1453.9
W8VA 02:14 7.071    1576.5
KD9IPZ 02:31 7.070    1333.9
VA3TPS 02:56 7.071   1694.3
NT7H 03:26 3.581 673.0
W6ZE 03:40 3.581   596.0
NV7AV 03:42 3.581   392.0
K7KY 03:46 3.581 632.7
W5RRR 03:50 3.582 1242.8
WB6AGE 03:55 3.581   662.0
W7PIG 12:51 3.581   704.9
K7UVA 12:53 3.580   59.6
W5PDO 12:59 3.580   477.6
W9LRC 13:05 3.581   1248.8
KE8RV 13:07 3.580   1500.0
W4SHL 13:23 3.581 1480.6
KB9REV 13:28 3.581 1251.8
K1KRN 13:50 7.071 2020.5
VE3YRA 14:12 7.071 1660.1
K5LRW 14:39 7.072 660.1
K5WXV 15:06 7.071 1007.9
K7IRA 15:26 7.070 511.6
KE6SHL 15:40 7.071 507.5

Callsign, date, and time from my Winter Field Day Log
Distance from QRZ.com
Total QSOs 62

Distance
1041 miles average
2020.5 longest
59.6 shortest

73,
Keep On Ham'n
______________

* - High SWR has little to do with how well an antenna radiates RF. The losses experienced due to high SWR are losses in the feed line especially coaxial cable. The primary reason for keeping the SWR low is to keep the finals in the transmitter from overheating and being damaged. That is why I have kept my coax to 20 feet. And yes there are losses in the tuner due to adjusting for the miss match. I try to look to "on the air" performance when judging an antenna.

Heads up on TV twin lead J-Pole antennas

2019-10-16T11:33:00.000-07:00

Just a heads up on making roll up J-Poles from 300 Ohm TV twin lead.

I've made a number of these antennas for emergency services use. They are a great antenna for a grab'n'go kits to say the least. I am fully in favor of having several around not only in the grab'n'go but in the glove box of all your vehicles and even backpacks and briefcases.

However, building one is not as straight forward as many internet sites make it seem. The problem comes with different types of 300 Ohm twin lead. There is the brown poly and milky white poly. There is the low loss foam filled also. EACH OF THESE HAS A DIFFERENT VELOCITY FACTOR! This can DRASTICALLY effect the measurements necessary to bring the antenna into resonance (low SWR) on the band on interest. I have personally experienced as much as 4 inches difference in the overall length. Also the placement of the coaxial cable feed point as will as the point to cut the gap can change from type to type.

I suggest you be prepared to build at least two antennas. The first one to modify by cutting or adding wire, moving the feed point and the gap until you find the correct measurements for the particular twin lead type you are using.

PLEASE don't let this discourage you from building this very useful antenna. Consider the work a learning experience in antenna engineering.

I've not posted instruction on building a twin lead J-Pole because there are many sights with the necessary measurements.

Here's a good starting point.
https://www.arrl.org/files/file/Public%20Service/TrainingModules/jpole-dual-band.pdf

If you intend to use your J-Pole on 2 meters and 70 centimeters be sure to check the SWR on both bands. The dielectric value can also effect the antenna's SWR on 70 centimeters. I have built separate J-Poles for each band to avoid the problem.

An Off-Center-Feed Antenna for 160 through 10 meters

2018-05-27T12:48:00.001-07:00

It's been a long time since my last post. Life and laziness intervened, mostly the latter.

This antenna is not for small spaces. It is nearly 250 ft long but is you can manage to negotiate successfully with neighbors or have the space I believe you'll find it's worth the effort.

I have spent some effort on this particular antenna researching the commercial market and test my homebrew version that is shown here.

Commercial antenna's tend to use matching networks (baluns) and coax feed systems so I started out trying that arrangement on mine.

All the antenna wire used on this antenna is #16 AWG copper clad steel from Davis RF tuned to the low end of 160 meters. Overall length was 243 feet at 30 feet above ground. The feed point was set at 59.5 feet.

All feed line arrangement were first test with my MFJ-259b antenna analyzer and the data for each band was recorded for future reference.

First feed line arrangement - 100 ft RG8x with a 1:1 balun. On air performance was acceptable on 160 and 80 but poor at best on all other bands. The on the air performance agreed with the analyzer's measurements. A very poor match, > 5:1*, above 3.7 MHz. I operated this antenna Sept 2017 through Dec 2017.

Second feed line arrangement - I connected a 9:1 balun at the feed point and connected the same RG8x feed line. The analyzer measurements were told the story. It was apparent that the feed line loss due to mismatch was little better at 40 meters and up. much worse on 160 and 80 meters. No surprise here. I didn't even put the antenna on the air.

Third feed line arrangement - 78 ft of 450 Ohm ladder line from the feed point to the 9:1 balun just outside the shack, then 25 feet of RG213 into the shack to the radio.

This arrangement has performed well beyond my expectation 160 through 10 meters since January 2018. I've made over 2000 QSO world wide on FT8, CW, and SSB combined from Jan 2018 through May 2018. I also ran WSPR for many hours in band hopping mode both transmitting and receiving. I ran some spot checks using the CW Reverse Beacon Network (RBN) using my MFJ-464 CW KEY/READER in beacon mode by sending "TEST TEST DE K7PDW". The results were very acceptable with worldwide reports for both WSPR and RBN.

SWR readings on my IC-756PROII are as indicated below. The internal tuner will handle all the bands except 80 and 40 on the high end.

160 - 2:1 or less across the band
80 - 3:1 or less below 3.6MHz, 5:1 or higher above 3.7MHz
40 - 3:1 or less below 7.06MHz, 5:1 or higher above 7.15MHz
30 - 1:1 all the band
20 - 2:1 or lower for all the band
17 - 1:1 all the band
15 - 3:1 for all the band
12 - 3:1 for all the band
10 - 2:1 or lower below 29.2MHz
Not tested on 6 meters

I've had a 67ft doublet with 87 ft of 450 Ohm ladder line to a 9:1 balun with 20 ft of RG213 into the shack for years that I used for 40 through 6 meters. I have taken it down because this antenna out performs it so well. I now have an Arrow 52-4s four element beam on 6m.

If you have the space to erect this antenna, I recommend you give it a try. It's not very expensive to build, the balun being the highest price item on my system. I use a DXEngineering DXE-BAL450-H10-A balun (pricy). It is rated at 5kW on CW and 10kW on SSB. If you don't run over 100W then a less expensive one will work for you.

UPDATE: This design has proven itself over the past 7 month (today is Aug 3, 2018) If you have the space it is well worth the effort to build it.

160 Meter Inverted U Antenna

2015-10-20T09:19:00.000-07:00

This particular 160 meter antenna looks like a half square, but its radiation pattern and performance is more like a vertical and it is about 40% as big as a half square. If you have about 100 feet or so space it is a viable 160 antenna. I have used this antenna on the air with equally good to slightly better result as the vertical discussed in the previous posting (12/4/13). I have a friend who also use this antenna with the same results. His is inside a 90 foot wide lot.

Advantage of this antenna over the vertical is that it is much less complicated to build and uses a wire mat for the ground. The disadvantage is the space required for the antenna wire.

I started with 138 feet of #18 AWG wire. Finished length was somewhat shorter after it was trimmed to resonance. More on trimming and matching later.

Figure 1*

The section labeled 1 is 1 foot above the ground at the end nearest the ground (This section of the antenna should be put inside of PVC for safety due to high voltages). The section labeled 2 is 28 to 30 feet above ground. Section 1's length will vary with the size of the ground mat and antenna tuning. Section 2's length may also be varied, but the longer the better. Section 3 is connected to the top end of the matching coil (more on this later). Section 3 is 28 to 30 feet long. Note that sections 1, 2, and 3 are one continuous piece of wire. You trim section 1 to adjust the antenna to resonance. Be sure to put the PVC over section 1 after each change. It will effect the tuning of the antenna. The end of the antenna (section 1) may be as high above the ground as convenient. The shorter section 1 the better the antenna will perform, but not by much.

Note: Wire 1 can be higher then 1 foot above the ground. It is set to that during simulation to keep wire 2 as short as possible. Mine ended up about 3 feet on the antenna installation.

The ground mat is cattle panel (Photo 1), sometimes called hog panel. I use AWG #4 welded galvanized wire panels that are 16 ft by 4 feet wide. (They're really 52 inches wide.) The mesh is about 4x6 inches for the ones I used. So long as the longest space between wires is less then .01 wavelength the mat will work. I use 4 of these panels to form a 16 x 17 foot ground plane for my 5-BTV vertical and it works well 80 through 10 meters even though .01 wavelength on 10 is about 4 inches.

Photo 1

The following table shows the simulation result for 4 different sized ground mats.

Mat dimensions Gain dBi Elevation angle deg.
8 x 16 (128 sq ft) 2.31 46
16 x 16 (256 sq ft) 3.72 49
16 x 32 (512 sq ft) 3.53 43
32 x 32 (1024 sq ft) 2.84 40

Table 1

Notice that bigger is not better as far as gain but does effect elevation angle in most cases. However, in the real world I suspect that ground differences will have a greater effect than mat dimensions on gain or elevation angle as long as the mat does not get too small. I would not recommend anything smaller then 256 sq ft over average soil. The gain drops off rapidly as the mat gets small then 256 sq ft.

I use the 16 x 32 mat and the on air performance is somewhat better than the vertical discussed in my Feb 2013 post. My mat lays on the surface, not buried. I've not tried burying a mat in any of my on air tests so I cannot comment to the effect of that except to say that the life of the mat will decrease with burial. I only put the mat down after the last lawn mowing in the fall and take it up again in spring. The 16 x 32 shape is dictated by my installation space. It is the overall area that counts. I built a 40 meter vertical where I use a plus shaped mat made of two pieces of 4 x 16 foot welded chicken wire and it worked great. So you can make your mat nearly any shape so long as you connected near the geometric center to preserve the antenna's radiation symmetry.

Ground Mat Construction Notes - I connect the panels together in three places along the 16 foot side and one place on the 4 foot side with split bolts (Photo 2, 3, 4) from the local electrical supply or Lowe's. These are used to make ground connections and come in several sized. I also recommend putting copper bearing anti-seize on the bolts if you intend to do as I do and take up the mat each spring. Loctite 39650 Copper Anti-seize comes in 8 oz bottles and is less then $10. It will last you nearly a lifetime. (I use it on all my ground connections and in extremely small quantities on coax connectors, power plugs, etc. This stuff is very conductive so don't let it get on the insulation between conductors.) I also use one of these to connect the loading coil to the mat and a small one on the loading coil for an adjusting tap.

Photo 2

Photo 3

Photo 4

Loading Coil Construction Notes - The loading coil (Photo 5) is wound from bare AWG #14 on 18 inches of 1 1/2 PVC which is 1.9 inches outside diameter . Wind 16 turns over 16 inches of the form. As you wind on the 4th turn attached a small split bolt on the wire and finish winding the coil. The split bolt is where you will attach the tap for the coax center conductor. The split bolt will slide along the wire allowing you to adjust the tap. I prefer this method rather then solder and unsolder.

In the final installation, I used a SO239 connector with 15 inches of wire soldered to the center pin and 2 inches soldered to the ground. This gave me enough wire to reach from the tap on the coil and solder the ground side to the bottom of the loading coil. As you can see in Photo 5 the bottom of the loading coil is then connected to the ground mat with a split bolt.

Note: Photo 5 is of the first loading coil I build. I later went with 16 turns on subsequent antenna. It proved easier to locate the 50 Ohm matching point.

When you reach the final adjustment carefully apply anti-seize to the wire then slide it into the split bolt. It is a good idea to put some anti-seize to the thread of the split bolt in case you need to remove it later.

Photo 5

Bringing the antenna into resonance is fairly easy. If you have an antenna analyzer use it, else an SWR meter will do the job as well. Adjust the length of the antenna to the center of the part of 160 you wish to operate the most. Don't worry about SWR value initially, just look for the frequency where the SWR is lowest. If it is close to the desired operating frequency, then adjust the tap on the coil for lowest SWR. You will find that moving the tap will change the lowest frequency some. Usually it is not enough to matter, but the two adjustments are somewhat interactive.

This antenna is a viable compromise. I've had many hours of fun QSOs and contesting with mine. Hope you give it a try and enjoy 160.

* - The red lines on the drawing of the antenna are artifacts left from my EZNEC simulator. They are not part of the antenna.

APOLOGY TO READERS

2013-12-04T15:33:00.000-08:00

Long before now I had intended to have posted information on another 160 antenna. I have been fighting a noise source in my neighborhood for several years but it never would stay on long enough to track it down. It has continued to get worse and finally put me off the air below 20 meters this summer. I believe I have now found it and expect the power company to fix it soon.
That accomplished, I will finish the on the air testing and post the information on how to build it soon.

Dave, K7PDW

BACKYARD ANTENNA FOR 160 METERS: The Vertical

2013-02-15T13:01:00.000-08:00

Over the past few years I've experimented with three different antenna configurations for 160 meters. Let me say up front that I have had positive results with all three and have been happy with their performance. I keep changing them because I only have them up during the winter and I like to experiment with new antenna designs. I have use all three on CQ World Wide 160 Contest, SSB with similar result each time.

For this posting I will discuss a vertical design. This is the most difficult of the three to build, but it will fit in a very small area. I would not advise it for a new ham without another ham with antenna adjustment experience to help.

Because I had it, I used 27 feet of 2 inched, outside diameter, aluminum irrigation pipe. The large diameter metal pipe makes the antenna easier to tune. The antenna can be built with other sizes or even wire*, but this set of instructions is for 2 inch OD pipe. I would recommend using this size if at all possible.

Please be sure to read all the instructions before starting to build.

Use a 2 inch outside diameter pipe with a coil at the bottom for impedance matching and a tuning coil at the top with three 102 inch CB whips for the top-hat tuning capacitor (see drawing below). Use 2 inch schedule 40 PVC for the top and bottom coil forms. The bottom piece also serves as the antenna's insulator.  Two inch ID PVC makes 2.375 coil form.  I would not use a small coil form in this application.  The irrigation pipe slides right inside PVC. Mine was a snug fit but it still needed help to stay in place.

COIL FORM PREPARATION
Cut off two 36 inch pieces of PVC for the bottom and top of the antenna. You will use 3, 1/2 inch #8 sheet metal screws the hold the PVC in place at both ends of the irrigation pipe; six screws all together. These screws must go through the PVC and the metal pipe. When you mount the PVC, it is best to pre-drill small "pilot" holes for these screws. Make sure the holes are small enough to assure that there is solid electrical contact between the metal pipe and the screws. Slide the PVC down over the pipe 3 inches and drilled the pilot holes about 1 inch up then slid it off again. If the PVC is a tight fit you may want to drill the pilot holes when you attach the the PVC permanently to the metal pipe. What ever you do, be sure to draw a line with a permanent marker from the PVC onto the pipe before you slide the PVC off so you can easily align the holes later. Two marks on the bottom and one on the top PVC so you can tell which end is which later.

MATCHING COIL CONSTRUCTION (Bottom end of the antenna)
The make 14 turns of #12 AWG spaced out over 18 inches on one piece of PVC for the bottom coil. (You will use bare wire here.) If you cannot find #12, #14 or #10 will be fine. (Smaller than #14 is not advisable.) Start the coil by making a half turn around a sheet metal screw the you place 18 inches up from one end. This screw holds the bottom end of the coil. Wind on the wire so that it ends about 1 inch below the other end of the PVC and tape it in place. The remaining 18 inches at the bottom to provides the bottom insulator for the antenna. Later the ground plane and the coax shield are attached to this same screw after the antenna is tuned.  For not just attach the bottom end of the coil. Attach the PVC with the matching coil on it to the metal pipe as described above with three sheet metal screws.

TOP HAT AND TUNING COIL CONSTRUCTION (Top end of the antenna)
To mount the CB whips in the top end of the second piece of PVC, use 5 or 6 inches of the same metal pipe to slide inside. Do not slide the top of this metal pipe down past the top of the PVC. The should be even. Hold it in place with one sheet metal screw near the bottom end of this piece of metal pipe.  Standard CB whips use 1/4" - 20 mounting studs on the bottom end. Drill three 1/4 inch holes equally spaced around the top end of PVC. These holes need to go through the PVC and metal pipe about 1/2 inches down from the end of the short piece of metal pipe. (I tried it with just large washers to support the whips and they pulled out of the PVC in just a couple of weeks.) Do not drill the holes for the whip more than 1/2 inch down or it will be next to impossible to tighten the nuts on the whips.  This short piece of pipe will connect the CB whips and the top end of the the tuning coil together in the finished antenna as well as providing the necessary strength to support the CB whips. Do not attach the whips yet.

The tuning coil at the top of the antenna may the same wire as the matching coil at the bottom, but this wire must be insulated. Regular #12 solid wire that is used in house wiring works well. Now make 100 turns close wound along the PVC. Start the bottom of coil by connecting the wire to one of the 3 sheet metal screws that will hold the top piece of PVC to the metal pipe. Temporarily tape the top end of this coil in place because you will have to adjust the spacing to tune the antenna. Later you will place another sheet metal screw to hold the wire in place but not now because you do not know where it will have to be. Now make 5 more turns to reach the top of the PVC and tape it in place. Leave about 24 extra inches before cutting the wire. This extra wire may be needed during the tuning adjustment and will be trimmed off later after the antenna is tuned. You will have to strip off some insulation to go under the screw that holds the short piece of pipe inside the PVC. Loosen this screw and slide the wire under this screw. Tighten just enough to hold the wire in place and make electrical contact. Do not bend the wire around the screw! Let the extra 24 inches just hang out in the air. Do not wrap it around because it will change the tuning. Putting this wire under the screw connects the top end of the tuning coil to the CB whips.

Now attach the PVC to the metal pipe. Put a piece of tape around the bottom of the coil next to but not over the screw holding the wire. You will have to back off the screw holding the bottom of the tuning coil while you attach the PVC. Install all three screws at this time as described above.

Now prop the antenna up on a ladder or such and install the CB whips.

ANTENNA SIGNAL GROUND MAT CONSTRUCTION

If your back yard is like most the ground radials are a problems because they need to be 138 to 140 feet long. And if you bury them you will need not less than 16 of them for reasonable performance from the antenna. This is not do-able for most backyards. If you live in a climate where the lawn is not mowed during the winter months (the best time of year for 160), the solution is a ground mat. Buy a 50 foot roll of 48, 60 or 72 inch welded wire fence (bigger is better). I've used 2 x 3 inch mesh with good result but almost any available mesh works fine. This must not be woven wire. Woven wire does not have good electrical connections and will not work well. Welded wire is available at most any "farm store". (Caution: Do not try plastic covered fencing. The wire in this type of fence is not welded. It depends on the plastic to hole it together.) You can bury the mat under the sod but it is best if left on the surface. I did say this was a before the snow, winter only installation, right? Unroll the fence and cut it at 25 feet or in half. If you have room for a larger ground mat, it is even better. Place the two lengths of fence about 5 feet apart and parallel to each other. Solder** wires between the two halves about every 2 1/2 feet to span the 5 foot gap. You can use the same bare wire used for the matching coil. Run another wire down the center of these connecting wire and soldered it to each wire that spans the 5 foot gap. "Pin" the fence to the yard with wire "v's". I had a supply of old wire coat hangers which I cut the hook part off where it was bent out for the shoulders and then cut the "de-hooked" piece in half to make 2 pre-shaped v's from one hanger.

TUNING IT UP
Now raise the antenna as near the center of the ground mat as you can. Please watch out for overhead electrical wires. If the antenna come in contact with them, it is deadly to anyone in contact with any part of the antenna or the coax or even your transceiver. Use guy ropes to hold the antenna vertical, but do it so you can easily lower and raise the antenna. Do not use metal guys for this antenna.

Prepare a wire to go from the bottom of the matching coil to the nearest point on the ground mat. Do not connect this wire to the coil at this time.

If it is not possible to place the antenna at the center of the mat, arrange things so the antenna can be easily connected to the ground mat with as short a connecting wire as possible. If it can only be connected at one corner of the mat so be it. It is best, however, to connect to the wire going along the center of the gap as near to the center of the mat as practical. Do not run the connecting wire over the mat. This will cause you problems. Connect it to the nearest point on the mat.

Connect the shield of your feed coax to the wire that connects to the ground mat. DO NOT connect the bottom coil right now. Now connect the center conductor of the coax to one of the sheet metal screws that hold the metal pipe and the PVC in place on the bottom end of the antenna. There must not be any connections to the bottom coil at this time. You are finally ready to adjust the tuning coil at the top of the antenna.

Connect your transceiver to the coax back in your shack. Be sure to use the same coax you plan to use when the antenna installation is completed and you are on the air. This should be 50 Ohm coax. Set your transmitter to its lowest power setting. If your transmitter does not have a SWR meter built in, put one in the line at the transmitter end with a short (2 to 5 foot) coaxial jumper cable.

Set the transmitter up 10 kHz from the bottom of the band and transmit long enough to read the SWR. In all likelihood it will be very high. Record the SWR. Move up 10 kHz, transmit, read and record the SWR again. Continue this until your last measurement is 10 kHz below the top of the band. The difference in the reading may be very small, but there should be some difference.

If you are lucky, the lowest reading will between the bottom and top of the band. If, however, the lowest reading is at the bottom of the band, the turns on the tuning coil, at the top of the antenna, are too close together. Lean the antenna over and try doubling the space between the top 20 turns or so. Re-tape and adjust the wire under the screw at the top end as needed to take up any slack. It is usually necessary to tape the coil in several places to keep the spacing in place. Remember to keep bare wire under the screw at the top end of the antenna. It may be necessary to strip off more insulation.

If the lowest SWR is at the top end of the band, loosen the screw and the tape at the top end of the coil and add a couple of turns to the coil. Re-tape and fasten the wire under the screw again keeping bare wire under the screw at the top end of the coil.

Once you make an adjustment to the coil, stand the antenna back up and make the SWR measurements again. Keep measuring and adjusting until the lowest SWR is in the part of the band where you intend to operate the most. You might not get the SWR lower than 10:1 or even higher. If you are very lucky you may get it to 4:1. This high SWR is to be expected. You will adjust the rest of the SWR out when you adjust the matching coil, but you must first get the antenna on frequency by adjusting the tuning coil for the lowest SWR.

NOTE: It may be that you will need to remove or add some turns from the coil but first keep trying by adjusting the spacing on the coil. Spacing the turns farther apart raised the antenna's frequency while adding turns and/or pushing them closer together lowers the frequency.

Once the lowest SWR is where you want it, secure the top of the coil where it transitions to the 5 widely spaced turns that reach the screw that connects to the CB whips with a sheet metal screw. The wire does not have to be stripped. Do this by placing a sheet metal screw right at that transitions from the closer wound lower part of the coil. The wire should only bend part way around the screw to stabilize the upper end of the close wound part of the coil. This has been held in place by the tape up till now. Tighten the screw down against the wire just enough to keep the wire from jumping out from under the screw. A washer may help to hold the wire here. Now make the 5 turns up the PVC to the screw that holds the short metal pipe that holds the CB whips. Take a turn most of the way around this screw and tighten it down. Trim off any excess wire.

Now "paint" the tuning coil with a thin coat Liquid Electrical Tape. Only paint the wire that is not covered with tape. Once it has completely dried, carefully removed this tape taking care not to move the wire and paint over the places that were under the tape. Once this coat has completely dried, paint the entire coil again. The goal here is to weather proof the close wound part of the coil. It is a good idea to paint over the wide spaced wire too to protect the insulation from UV from the sun, but the screws will hold it in place if you carefully take out the slack.

Raise the antenna once more and check that the SWR is still about where it was before you painted the coil, made the final connections, and trimmed the wire. It may change a little, but it should not have changed more than 25 kHz. If it has change more than that, the spacing on the coil has changed and it will need to be fix before you continue, so take great care not to move the wire while finalizing the top coil.

NOW THE ANTENNA IS FINALLY TUNED. You are ready to adjust out the SWR with the matching coil at the bottom.

MATCH IT
First, disconnect the center conductor of the coax from the antenna. Second, connect the coax shield and the ground mat to the screw that holds the bottom of the matching coil. Third, make a short flexible insulated wire, 18 or so inches, with an alligator clip attached to one end. Solder the other end of this wire to the center conductor of the coax. Connect the top end of the matching coil to one of the screws holding the metal pipe and the PVC in place. Clip the alligator clip up about half way up the matching coil.

Back in the shack, tune your transmitter to the frequency where you measured the lowest SWR during the tuning coil adjustment. The measure and record the SWR. (Do not change the transmitter's frequency during this process.) Move the alligator clip up or down one turn at a time and measure to find the lowest SWR. Now you can move the alligator clip around that one turn in the coil to see if the SWR will go lower. Be sure not to wind the wire with the alligator clip more than 1/2 a turn around the coil and keep it as far away from the coil as reasonable. If moving the clip in either direction makes SWR worse, leave it in the original position. Don't move the clip more than 1/4 turn at a time. Remember you should not have to go more than 1/2 way around the coil in either direction during this process or you will be on a different turn. It is not likely that moving the clip will make enough change to worry about but in rare cases it will so it should be checked. You should be able to get the SWR down to around 2:1 or less. Yes a tuner will be necessary with this antenna especially if you want to be able to tune the entire band. Even if you get the SWR lower than 2:1 when you change the transmitter frequency very far the SWR will climb rapidly. It is the nature of antennas with tuning coils to behave that way. You may even find that your tuner will not adjust over the entire band.

Once the lowest SWR is found, you may want to remove the alligator clip and solder the wire in place so it does not get moved or knocked off. It is a good idea to paint the bottom coil with liquid tape so the coil will not move around. That would change the tuning of the antenna.

Your antenna is FINALLY ready to use.

By now you are wondering why I do not just give you the correct number of turns for everything. That is because the ground system you build, be it radials, a mat, or clipped onto a chain link fence (not recommended) will cause the coil adjustment to change drastically. You may have to change the number of turns on the tuning coil if adjusting the spacing still does not tune the antenna. I can only hope to get you in the ball park. The rest is up to you.

NOTE: The ground symbol in the illustration is used to indicate your ground plane. It is not a bad idea to also provide a ground stake at the base of the antenna. But a ground stake by itself will not be a sufficient signal ground. The antenna will probable tune up without a ground plane but its efficiency will be very low and the antenna will not perform satisfactorily.

- Liquid Electrical Tape is usually available at WalMart in the automotive section or at an electrical supply house.
- 2 inch aluminum tubing is available online in 8 foot lengths. It would be necessary to "couple" these together some how. A scrap yard may have something too. If you live where agriculture irrigation takes place, you might try ag pipe supplies. Mine came from a farmer who was changing to a different irrigation method. I bought it for scrap price. I do not recommend using smaller than 2 inch because the top hat (CB whips) places a lot of stress on the pipe especially while raising and lowering the antenna.
- Schedule 40, 2 inch PVC is available at most any home improvement store or hardware store. I recommend that you stick to this PVC because it has the strength needed and the coil winding info here is based on the OD of this type of PVC.

* - I would use as large of wire I could manage, not smaller than #10 AWG if you use wire instead of pipe.
** - Some of this type of fencing is galvanized, making soldering difficult. You may want to use split bolt connectors for this job. They are available in the electrical department of home improvement centers.

----------------------------------------------------------------------------------------------

Next time I'll talk about a Marconi antenna for 160 meters. This requires a little more than an average backyard and has a few special considerations for erecting, but it is much easier to tune up and get on the air. Every antenna has it's compromises.

FEED LINE CHOKE FROM COAX

2012-12-12T09:53:00.001-08:00

Over the years coiled coax has been used to choke off RF from the outside of coax feed lines. Sometimes these are called 1:1 baluns, choke balun, but technically a balun is an impedance transformer while these coils are chokes. (NOTE: This discussion is limited to air core chokes only.) The reason for a choke is to stop RF from coming down the coax, causing distortion of the antenna’s radiation pattern and RF problems in the shack.

Coax line chokes work well if they are used correctly. However, there are some things one needs to know about using this type of coax line choke.

1 1. They are most effective on one band only below 40 meters.

2 2. If carefully designed, they will perform on more than one band 40 through 10 meters (see chart below).

3 3. Always “flat” wind these chokes. Scramble winding adversely impacts their performance.

The most important performance limiting factor is inner turn capacitance, called parasitic capacitance.

Remember that any time two conductors are next to each other, even if there is a DC electrical connection between them, there still is some capacitance between them at radio frequencies (RF).

NOTE: Do not confuse parasitic capacitance with the capacitance between the shield and the inner conductor of the coax. The capacitance between the shield and the inner conductor does not contribute anything of significance to this discussion.

As parasitic capacitance gets larger the choke starts to look more and more like a capacitor to RF. Remember that a capacitor's or an inductor's resistance to alternating current (AC) varies with frequency.

Experience over the years has shown that 10 times the feed line resistance for a well match antenna is a good number to use for a coaxial line choke's reactance. I used 500 Ohms for creating the chart below. In the real world up to 25% either way is acceptable. That is 375 to 625 Ohms. A choke will remain effective so long as both its coil and parasitic capacitance remain in the acceptable range for the expected operating frequency.

The following chart gives a list of coaxial line chokes for various ham bands.

Turns Diameter Height Coax type Band Coverage

13 8 3.25 RG-174 160 meters only

RG-58

RG-8x

9 9 3 RG-174 80 meters only

RG-58

RG-8x

8 6 2 RG-174 40 meters only

RG-58

RG-8x

9 4 2.25 RG-174 40 – 30 meters

RG-58

RG-8x

8 4 2 RG-174 30 – 20 meters

RG-58

RG-8x

5 5 2 RG-174 20 - 15 meters

RG-58

RG-8x

6 4 2 RG-174 17 - 10 meters

RG-58

RG-8x

4 3 1 RG-174 6 meters only

RG-58

RG-8x

Height and Diameter are in inches.

Be sure to match the length of the coil keeping the spacing even between turns. This may require using a spacer between turns while winding the coil. Once the coil is wound the spacer should be removed and the turns need to be glued in place. Deviating very far from either length or diameter will chance the frequency at which the coil will work.

Here are three graphs that will help you see why a coaxial line choke is limited. Note how rapidly the inductance and capacitance very with frequency. Notice that on each graph inductive reactance and capacitance reactance cross on 500 Ohms. Remember from above that this is the design criteria.

Notice the higher the band, larger the range of frequencies the choke covers.

Other coil sizes and coax types will work. However, they are too numerous to post.

Dave, K7PDW

SMALL BACK YARDS - THE BANE OF HAMS

2012-06-29T15:04:00.000-07:00

It seems that there is an assumption that if you have a small backyard you are doomed to some sort of compromise antenna. My response to that dire prediction is, “It isn’t necessarily so.”

If you have 70 feet in a straight line that you can put up a wire even at 15 feet above the ground, you have what it takes to make a simple (no traps, no ground radials, no compromise) antenna that will work well from 40 meters through 10 meters and even 6 meters. (Please remember to be cautious of power line when installing any antenna system. They’re real killers.)

It turns out that the simplest antenna to build is one of the best radiators of RF. Sixty seven feet of #14 copper wire with a convenient length of either 300 Ohm TV ribbon or better 450 Ohm ladder line for feed line will do the job very nicely. Bring the feed line down as perpendicular to the antenna as possible. It does not have to be perpendicular to the ground as long as it stays 8 feet or so above the ground. When you get to where you want to enter your house install a balun. Here a 4:1 balun will work with most tuners and 450 Ohm ladder line, but I prefer a 9:1. In my experience more tuners, both built in and stand alone, perform better with 450 Ohm ladder line and a 9:1 balun. If you use 300 Ohm TV ribbon then a 4:1 is a better choice unless you can find a 6:1 balun which would be ideal. You should be aware that TV twin lead has more loss than ladder line, but both beat an all coax feed line in this application by a country mile.

This antenna performs as a common ½ wave dipole on 40 meters. On the higher bands it behaves as a collinear. That is why you want to feed it with twin lead or ladder line. Ladder line is preferable because it has significantly less loss than TV lead. You may be tempted to put the balun right at the feed point of the antenna and then run coax all the way back to the transceiver. That will work but the loss in the coax will be very high especially 17 meters and up.

Here’s why. There is a common misconception that by putting a balun in the feed line even when there is a high SWR that somehow the balun will correct the mismatch. This is just not true. The balun only transforms the mismatch to another value that may or may not match the feed line impedance. The feed point on this antenna and most collinear runs from 20 Ohms to 800 Ohms depending on the frequency you are running. The following table compares the loss between a balun at the antenna feed point and 70 feet of RG58 and 60 feet of 450 ladder line between the feed point and a 9:1 balun then 10 feet of RG58 to run through the wall to the tuner and transceiver in the ham shack.

BAND 60 ft ladder line and 70 ft RG58 with a balun 70 ft RG58

10 ft coax w/balun at the ant feed point no balun

--------------- ------------------------ ----------------------------- --------------

6 meters 8.52 dBi ERP 5.84 dBi ERP 3.93 dBi ERP

10 meters 7.84 dBi ERP 4.89 dBi ERP -2.66 dBi ERP

12 meters 8.24 dBi ERP 6.10 dBi ERP 0.21 dBi ERP

15 meters 6.96 dBi ERP 4.65 dBi ERP 4.50 dBi ERP

17 meters 8.34 dBi ERP 5.79 dBi ERP -1.58 dBi ERP

20 meters 6.83 dBi ERP 4.02 dBi ERP -3.14 dBi ERP

40 meters 5.71 dBi ERP 4.37 dBi ERP 5.67 dBi ERP

ERP – Effective Radiated Power for the antenna system

Note – I did not have the necessary loss specs for TV twin lead for this comparison, but it will fall somewhere between 60 ft ladder, a balun with 10 ft of coax arrangement and the all coax with a balun arrangement.

Another misconception is that an antenna must be resonant to radiate. This is also not true. The loss of signal strength in a non-resonant antenna system is almost always due to high loss in the feed line caused by mismatch between the feed line and the antenna’s feed point. A low loss feed line such as ladder line, TV ribbon, or open wire feed line carries the transmitter’s power to the antenna where it is radiated efficiently despite high SWR cause by non-resonance. The performance of a non-resonant antenna will be comparable to a resonant antenna when feed line losses are kept to a minimum. However, you must still do something to prevent the high SWR from damaging the transmitter. This is the job of a tuner. For multi band antennas that do not have provisions for achieving 50 Ohm feed point impedance at all the expected operating frequencies, a low loss feed line and tuner arrangement is a reasonably inexpensive solution. Another solution is a remote auto-tuner at the feed point of the antenna. This is effective, but considerably more expensive. And it is often difficult to manage the weight of the auto-tuner at the antenna’s feed point unless it also happens to be at one of the antenna’s support points. If an auto-tuner is available, it will work just as well at the end of the ladder line where it enters the house. If you use an auto-tuner be sure it has provisions for feeding a balanced line. If not, then a balun will be necessary between the balanced line and the auto-tuner. It would be best to check with auto-tuner manufacture about how to implement that.

Some will note that this antenna looks suspiciously like a G5RV and that is a valid observation. The major difference is that the balanced line can be any convenient length and the coax can thus be kept to a minimum length. In this type of antenna one should always try to achieve the shortest run of coax possible and thus reduce the feed line losses to a minimum. It is true that the balanced line that is cut to a specific length on the G5RV does act as an impedance matching device. But again it will provide a good match at some frequencies and not so good at others just like a balun. The loss that occurs in the coax will still be present. So always keep the coax as short as possible and the balance line as long as is sensible so as to reduce the loss in the antenna feed system to a minimum.

Happy HF’n and 73

K7PDW

PS - By the way, this antenna can be bent or sloped but its efficiency will drop some and often the bandwidth will get narrower making it difficult or impossible to tune some bands.

Back To Back Mobile Whips For Portable Stations

2012-05-12T15:06:00.001-07:00

Back to back mobile whips have long been used to create rotatable portable dipoles. You may have heard varying reports on how well they work. Some folks even claim that they are nearly unusable because of high SWR. My experience working contests while portable QRP with them has been good. My setup has good SWR and I don’t seem to have problems making contacts with my FT-817 on SSB. I was actually please with the ability to turn the dipole in null out strong signals. The one disadvantage I found was that my setup only covered about 100k on the 20 meter band at less than 2:1 SWR. I expected that because it is the nature of wound antennas to have a narrow bandwidth.

I began to wonder why others had such bad experience with this type of antenna. I believe I discovered the reason when I began to consider buying a commercial mount design for back to back mobile whips. I noticed that the commercial version simply grounded one whip to the mount while insolating the other one as in a standard mobile installation. My home brew setup uses insolated mounts on both whips. I connect the feed line, coax, as any other dipole. Shield to one side and center conductor to the other side. I use a coaxial wound choke to control RF on the outside of the coax.

That got me to thinking. I decided to experiment with grounding one whip, the one connected to the coax shield as the commercial mounts are designed. I used a short jumper for the connection. I usually use about 18 inches of PVC as an interface between top of my mast and the antenna mount. I went ahead and set up the antenna as usual with the PVC as usual. I didn’t see any difference.

I next decided to try doing away with the PVC and connect directly to the mast still leaving the antenna and coax shield connected to the mount and thus now connected to the entire mast. The mast I was using is 4 foot sections of the military mast I bought off the surplus market. I have both aluminum and fiberglass sections. I had use the aluminum in the previous tests and did so this time.

This time the SWR exceeded 5:1 which is well out of the range of many automatic tuners. I grabbed my MFJ Travel Tuner Model MFJ-902 and was able to tune the antenna to an acceptable SWR. However, tuning the FT-817 more than a few kHz required retuning the tuner. I decided I was onto something but just to satisfy my curiosity I replaced the top two section of the mast with fiberglass sections. The SWR dropped down to where it was when I still had the PVC between the mount and the mast. I decided to confirm my result. I put the PVC back in place and went back to the aluminum mast section. The SWR remained low as expected.

So if you are considering back to back mobile whip, I would avoid commercial mounts that simply ground one whip to the mount unless you plan to use non-conducting mast material or at least 18 inches of PVC between the metal mast and the mount. I also recommend that you make provisions for keeping the RF off the outside of the coax. A 1:1 balun, ferrite beads, coax wound on a ferrite core or a coiled coaxial choke are all solutions for this. The coiled coax is the least expensive but if it is not constructed correctly it will not be as effective as one would like. This will be the topic of a future post.

K7PDW

SWR Changes When I Increase My Transmit Power

2012-05-03T09:22:00.001-07:00

Have you ever tuned up your rig running low power only to have it change when you increased the power? (It is recommended that you reduce you rigs power to its lowest setting when you tune up your antenna. This is so you will not cause accidental interference to ongoing QSOs or overheat your transmitter.) This becomes more of a problem as you begin to work the HF bands, but it may also happen at VHF/UHF particularly if you run a hundred watts or more.

What is the cause of this problem?

The cause is usually the RF from your antenna is coupling into some surrounding conductor that is not part of the antenna. This can be almost any piece of metal from a nearby wire to a metal building. It may not be noticeable on all bands but the cause is still the same. You may think the wire clothes line below your antenna is not a problem. But if it is within 15% of some part of the wave length you’re running, it may become resonant and start to radiate thus effecting you antenna. Remember this is how a yagi works. Wire or long metal objects such are metal rain gutter running in parallel to the antenna are most often the cause for most hams.

Should you be concerned?

Probably yes. 1) It will impact the way your signal leaves you antenna thus resulting in your antenna “not working as advertised”. 2) It can cause all the problems associated with high SWR. 3) Depending on what it has coupled to, there is a potential for someone getting RF burns, could cause RF on the feed line, and/or RF interference with other electronic equipment.

What is one to do?

The easiest solution is move the antenna. Try to determine what the antenna is coupling to. Metal objects are almost always the offender. Hidden wiring in building walls/ceilings or metal siding/roof are some of the more common problems. However, sometimes trees can cause this especially if they are beside the antenna. Trees at the ends of dipoles aren’t usually a problem nor are metal masts/towers. It is always good practice to use several feet of rope at the end of an antenna to isolate it from whatever you use to support it. (Don’t forget to use an insulator. Wet rope will conduct RF.)

However, things are not as bad as they might seem though. Generally moving one end of the antenna a few feet away from the offending conductor is sufficient to resolve the problem.

RF Gain Control

2012-04-27T12:30:00.001-07:00

So my HF receiver has a RF gain control. That's nice. What does it do?

The answer you will often get goes something like this. "Just turn it all the way up and leave it alone." Or, "It is just a leftover from the old days. It's kind of a traditional thing to put it in. Just leave it wide open." Or, "It is just another kind of volume control." Or, "Don't worry about it. Just leave it turned up and let the AGC do the work." All of these answers are true to a point. But modern HF receivers have RF gain for much the same reason as the old time receivers. Their main task is to reduce overload in the following stages of the receiver.

Copyright (c) 123RF Stock Photos

DON'T WORRY! A technical discussion is not about to follow.

Let's see. The question was, "What does it do?" In simple terms it can make a signal easier to understand and listen to. I find there are three situations where adjusting the RF gain helps me out.

SITUATION 1 - I am listening to a very very strong station and it sounds bad. I often will turn the RF gain down to the point that I have to turn the AF gain up. That will many times make the signal more "listenable".

SITUATION 2 - A ham neighbor near by is on the air. His signal is not splattering me but other signals seem to be weak or just don't sound as clear as usual. Turning down the RF gain some will often clear up the others signals that I am interested in hearing. This is most often helpful on the lower HF bands.

SITUATION 3 - There is a lot of static noise and the noise limiter just does not seem to help very much. Turn off the noise limiter and turn down the RF gain slowly. I often find that there is a point where the noise goes down more than the signal. I call this the "sweet spot". I may even turn the noise limiter back on. See note below.

If you don't encounter any of the above situations, then yes, leave the RF gain all the way up.

I most often reach for the RF gain when listening to weak signals in noisy conditions. By finding the RF gain's "sweet spot" on a signal it reduces my "listener's fatigue" and I enjoy my time on the air much more.

Hope you find this helpful and happy hamming.

NOTE: You may find that adjusting the RF gain with the noise limiter on works fine for you. It's easier for me to find the "sweet spot" with the noise limiter off on my radios.

What Is Ham Radio?

2012-03-09T12:57:00.000-08:00

The easiest answer “almost anything you want it to be”. That probably sounds trivial to someone not familiar with all the activities that hams find to include in their hobby. But take a step back and consider all the ways you communicate in today’s world that are not face to face. Cell phone is a two way radio. Email is available through packet radio. Skype is not unlike amateur TV. The list goes on. Ham radio uses GPS technology to provide positioning systems over radio link just like smart phones. Remote weather reporting techniques over packet radio links not unlike weather bug. Satellite communications and even radio communications bounced off the moon and meteor trails. Hams are converting WIFI systems to ham bands to set up communications networks for ham radio operations. Recently a group of hams launched and tracked a balloon across the Atlantic Ocean clear into the central Mediterranean. And what does that all mean. It means that ham radio is one of the most unlimited and diverse hobbies around. You can specialize in one or two areas or many.

Now if you’re thinking why would I go to the trouble and expense? I have a smart phone. To that I would say this. Ham radio still works when all other forms of communications fail. Hams are not dependent on internet, cell towers, phone lines, or even satellites. This is because most ham gear is designed to run from 12 volts. With almost any car battery and a length of wire for an antenna and a ham will get up and running.

Amateur Radio also has a public service aspect that many people don’t even realize. If you have been to a parade, a bike race, foot race, a community fair or celebration, or a public emergency that involved many people, there were probably several hams with their radios, providing communications services. These may have included traffic and parking coordination with the public safety folks, communications at first aid stations, sag wagon communications at bike races, lost children assistance, search party communications, communications for logistics at wild fires and other disasters, shelter communications in disaster areas, health and welfare messages in/out of disaster areas. The list is nearly endless. It might be said that ham radio operators are the silent communicators because we go unnoticed most of the time. We use our own equipment, provide our own transportation, bring our own food, water and shelter in many cases, and sometime even risk our lives so that messages, emergency and otherwise, get passed along. We do it all for love of the hobby and community service. We don’t get paid.

If you are reading this and you are not a ham, consider looking into the hobby. There is a niche for nearly every interest. If ham radio is not for you, that’s ok too. But next time you’re out and about at an event and you see that geeky looking gale or guy with a two way radio, ask “Are you a ham?” and a say thanks for helping out. He or she will probably be a little embarrassed and not know what to say, but it will be appreciated.

SWR vs Signal Strength Demonstration

2012-02-08T15:29:00.000-08:00

I first got started in amateur radio in the late 50’s. I lived in a small town in south central Idaho. That town had less than 2500 people and over a dozen hams. This was due mostly to the efforts of one dedicated ham, Ted Goers, W7ORB, now silent key (ham speak for deceased). Ted along with the owner of the local electrical shop, E.I. Shaw also a ham whose call now escapes me, were responsible for elmering most of the ham in town. Ted would have these sessions when he would demonstrate a ham radio principle, usually at the electrical shop. One of these really stuck with me. IT was an antenna with an almost perfect (1:1) SWR but almost no signal radiated. He was demonstrating that a good SWR does not necessarily mean that the antenna is any good at all.

He took an untuned mobile whip antenna that was mounted on an insulator with a coax connector. He had connected a coaxial T to the antenna. On the second leg of the T he connected a 50 Ohm dummy load. On the third leg he connected about 100 feet of coax. He connected a 125 Watt multiband transmitter. He first set up the transmitter for 80 meters. We check the SWR and it was 1 : 1. We tuned around and found a QSO going on and called of a break. After several tries one of the people in the QSO said, “I think I hear a station trying to break.” After a couple of tries the guy on the other end said, “I can tell there is someone in there but you’re signal is too weak to copy.” Ted switched to an 80 meter dipole he had up about 40 feet and tried again. The guy came right back with a 599 signal report 100% copy. We thanked him and checked the SWR on the dipole. It was 1.6 : 1 at the same frequency.

This not only points out that a good SWR doesn’t tell you much about the capability of an antenna system but points out the need for having someone check your signal strength.

Just to prove the point Ted then removed the T and put a tuner at the base of the whip. He tuned it up and broke back into the same QSO*. This time the signal report was 569 but armchair copy*. The whip was 9 feet tall standing on the ground with no ground radials for RF ground. In spite of the fact that this arrangement is an extremely poor antenna, it still was better than the perfect SWR “antenna”. And by the way the SWR on the whip with the tuner’s help was 1.9 : 1. That is a marginally acceptable SWR. As I remember the station we contacted was in California. Not a great DX* contact, but certainly not line of sight/local.

* - See Glossary

WEAK SIGNAL AND LOW SWR

2012-02-07T14:25:00.000-08:00

There are a number of things that can cause this problem. Here is a list of common ones.

Placement of the antenna

                Very long feed line
                High feed line loss
                Signal Ground Issue
                Local terrain

These apply differently at different frequencies. I’ll note this as I go.

Placement of the antenna - above 50 MHz

Higher is always better. Always place an antenna for VHF/UHF as high as your budget, safety, and local ordinances will allow. Keep it clear, as much as possible, of metal sheeting, metalized shingles, wires and cables, trees, even some types of glass in windows. Running a handy talky from inside a house, vehicle, or camp trailer is not going to work well at all. If you are lucky enough to be close to a repeater, you may get away with it. But simplex operation will be very marginal to non-existent.

Very long feed line - especially above 30 MHz

Feed line loss can seriously reduce the amount of power that arrives at the antenna. Use as low loss feed line as you can afford. Feed line loss is discussed in another post, “Feed Line - Introduction to coax”.

High feed line loss - gets worse as frequencies get higher

A feed line with high loss can mask a high SWR. Any signal on a high loss feed line loose power. It does not matter whether the signal going toward the antenna or being reflected back from it. (Remember SWR is a ratio of the RF leaving a source and that being reflected back toward the source.) When you measure your SWR at the transmitter end of the feed line, the reflected RF is lowered by the feed line loss too. So the SWR may be at an acceptable level but there still may be a mismatch at the antenna that is seriously impacting the signal strength. For this reason it is best to check SWR of a new antenna with a short piece of coax that is known to be good before you connect a long feed line or a feed line with considerable loss.

Local terrain - all frequencies but especially above 30 MHz

Generally radio signals are absorbed by soil. However, radio signals also reflect off soil and rock that is highly mineralized. So as a general guideline the best I can say is give it a try. You just never know. HF antennas placed in deep valleys or close to mountain ranges may suffer from poor performance.

Signal Ground Issue - especially below 30 MHz

I find an analogy first told to me by my Elmer (ham speak for mentor) helpful. “Radio signals want something to push against to get off the antenna.” A poor signal ground will reduce a signal’s strength just as effectively as high loss coax. Verticals at all frequencies are most susceptible to this problem. Long wire antennas also need good signal ground, especially random wire (length) antennas. Most VHF/UHF antennas have signal ground built in as radials that do not require tuning. (This doesn’t mean VHF/UHF antennas don’t need tuning.) Signal ground is the subject of another post.

VHF/UHF Dual Band Antenna "Feature" You Should Know

2012-01-31T15:34:00.000-08:00

Most dual band antennas available for VHF/UHF have a little discuss “feature”.

Maybe you have noticed that very few antenna manufactures ever give their angle of elevation[1] information for each band. They are very happy to share the maximum gain in dB for each band. However, there is a characteristic of most antennas that causes the higher frequency signal to leave the antenna at a high angle. It is not unusual for the major lobe on 2 meters to be less than 10 degrees while the 70 cm major lobe to be higher than 45 degrees. The truth of the matter is that there will usually be a secondary lobe on 70 cm that is lower than 10 degrees. But that lobe is not the maximum gain lobe. Now as far as operational performance, this is seldom a problem. The only time this may be noticeable is if you find that 2 meter signals are getting difficult to copy and change to 70 cm expecting to get an improvement in signal strength. You may still find that the signal is easier to copy, but this will most like be due to better signal to noise ratio[2] rather than a stronger signal.

So is this a problem to be concerned with. Generally speaking I’d say no. However, you should be aware of it and understand that the gain numbers you see in advertising are necessarily representative of an antennas performance in the real world.

There is one antenna, in my experience, that does have low angle at both VHF and UHF. It is the ARROW OSJ 146/440. See http://www.arrowantennas.com/osj/j-pole.html. It is one of the best antennas for the money. It is rugged build from aluminum rod not tube. It has good SWR on both bands. It is heavier than antennas made of tubing but still not unreasonable. I have one that I use for portable operation with my RV and just “out in the field”. It has been blown over while up on a 20 foot mast and didn’t even bend when it landed on a parking lot. I know a number of ham locally that own one of these and I have not heard one complaint.

[1] - Angle of elevation is the angle above the horizon at which the strongest lobe leaves the antenna. The smaller the angle number is the better for reaching maximum distance.

[2] - Signal to noise ratio is a measure of signal strength to the background noise, i.e. noise floor.

Radio Frequency Ground

2012-01-28T10:19:00.000-08:00

A good Radio Frequency, RF, ground is as important to having a strong good quality signal as a good Safety Ground is to a safe operating environment.

RF grounding is a very broad subject. It includes but not limited to topics such as coaxial shield, antenna elements, ground planes above, on and below the ground, in-shack grounding, baluns, coaxial chokes, bead chokes, sometimes called bead baluns, wave guides for the microwave folks, and the list goes on. However, for purpose of brevity this post will be limited to some approaches for preventing or solving RF in the shack.

First, how might you know if you have RF in your shack? Here is a list of common problems that indicate that you might need to work on improving RF grounding.

Getting RF burns from metal surfaces of the equipment

SWR fluctuations when you get near or touch metal surfaces

Reports of poor quality audio, usually a buzz or distortion[1]

Poor receiver reception or noticeable drop in receiver reception

A change, usually for the worse, in SWR[2]

High SWR on one band but not others

So what to do?

First, if this is a new problem, check all your ground connections to be sure that they are all secure. This means check that all coax connectors are screwed down snugly[3] and the same for all ground lugs on station equipment, ground rods, and all safety ground connection points.

There is one thing that I’ve observed many new hams doing that often is at the root of RF grounding problems. They fail to provide any type of RF ground at all in the mistaken idea that their safety ground will serve as an RF ground. This is not completely in error. The truth of the matter is that safety ground does contribute in some part. The problem is that safety ground is seldom sufficient for radio frequencies especially on HF. On higher frequencies this is not as often a problem in some part because most antennas for VHF/UHF provide built-in RF grounds.

RF grounding problems often show up at a particular band while other bands are fine. This situation is because something in the station installation is providing the necessary ground for all the frequencies except the one that is causing problems. This is particularly true for tuned random wire antennas that often used on HF. Almost all end feed wire antenna must have a tuned length counter poise[4] for each frequency of operation. I will have more on this later when I discuss random wire antennas.

In cases of balanced antennas fed with coax, a balun, be it wire wound, coiled coax or ferrite beads, will usually resolve RF in the shack problems. This point is often neglected when balanced antennas, such as dipoles, loops, and yagis are discussed. For best results with these antennas something should be done to accommodate the interface between an unbalance feed and a balanced antenna.

If you have installed a balun and still have RF in the shack, you might measure the feed line to see if it is a ¼ wave length[5] on the frequency that is giving you problems. Sometime a feed line can act as a “receive” antenna and pick RF. And it does not have to be the feed line that is in use. This is especially true if the feed line runs parallel or even close to parallel to the antenna that is in use. (Running feed lines in parallel to antennas should always be avoided)

The suggestions in the posting are by no means exhaustive. However, if you are having problems with an existing installation or are building a new installation the things discussed here should be followed as a minimum.

[1] - On VHF/UHF this might be multi-path. If the problem come and goes it may be multi-path. Multi-path will be the topic of a future posting.

[2] - This may take place slowly over time.

[3] - There was a recent article in QST where the author promoted using pliers for tightening PL-259 coax connectors. I would recommend using caution. This may be appropriate if you expect a lot of vibration such as a mobile installation. However, I cannot remember ever having a connector back off on its own. I recommend you use fingers to tighten connectors. If you expect vibration or encounter this then a turn or two of electricians tape will go a long way toward keeping things in place.

[4] - A counter poise is a length of wire cut for a specific frequency that provides a RF ground.

[5] - A quarter wave or multiple of quarter wave (¾ - 1 ¼ - 1 ¾ etc) can cause this to occur.

Ham Speak: A Glossary For New Hams

2012-01-21T18:32:00.003-08:00

A collection of definitions and links to amateur terms. It is by no means complete since ham radio is such diverse hobby. First some links then a alphatical list on terms I have use on this blog. Hope these help. I you find a broken link send me an email. My address is a t the bottom of the blog.

ARRL - http://www.arrl.org/ham-radio-glossary

armchair copy - easily copied,

antenna system - any equipment following transmitter's output up to and including the antenna. In some cases this may include RF ground equipment depending on the antenna type in use.

CW abbreviations - http://www.radiotelegraphy.net/prosigns.htm

DX - a long distance contact usually to another continant or some folks say over a 1000 miles
elmer - mentor

ERP - Effective Radiated Power, the sum of the gains and losses of the transmitter's power output that is transferred to the air by an antenna system

FB - Fine Business (very good, good idea, excellent)

home brew - home made

Mic fright - being reluctance to make that first contact

QSO - talking or making a contact. For more see this List of Amateur Qsigns

QSL - I understand or do you understand, also a cards ham exchange to confirm contacts

silent key (sk) - deceased, sometimes with a call sign such as "W7ORB, sk"

FOR LOOK AT HAM SPEAK FROM A HISTORICAL PERSPECTIVE SEE http://www.ac6v.com/73.htm

Safety Grounding

2012-01-18T13:34:00.000-08:00

Grounding can be a very complex and confusing topic. Therefore, many hams ignore it and hope for the best.

I’ve heard folks say, “My power supply is grounded back through the wall and my radio is grounded to that. That’s good enough, isn’t it? The radio works fine.”

This is a damaged radio waiting to happen. Nearby lightning, let alone a nearby strike, has the potential to cause damage in this type of an installation. If you are stuck with this arrangement, like in an apartment or hotel room, then you must disconnect your power supply from the wall and disconnect you radio from the antenna whenever they’re not in use.

It is also important to make sure that the antenna connection is at least a couple feet from any conductors even the house wiring. If at all possible connect your antenna to a ground connection that is not part of the house wiring. I know of a case where an arc jumped about eight inches from a dangling antenna connector to a wire running from a power supply to a radio and destroyed both the radio and the power supply. The antenna had not even been hit directly. The hit was on a fence several feet from the antenna mast. The mast’s base was buried in the ground. This can be thought of in simple terms as the antenna and its feed line act as receiving antenna very close to a one terawatt[1] transmitter, i.e. the lightning strike. There are inducted voltages like go on in a transformer too. The point is, it does not take a direct hit to cause a lot of damage.

So what to do? Here is a link[2] to a very good discussion on some practical things you can do. My recommendations are as follows

First, read “House Ground Layouts” carefully

Second, see what others have done

Third, read “House Ground Layouts” carefully again

Last, put in the best system you possibly can

One thing I should mention here. Most modern ham radio equipment has a lug of some sort to attach a ground wire. One should not fail to connect this to ground. The owner’s manual for the equipment will have recommendations for this connection. This becomes very important for radio frequency, RF, ground and needs to be done properly.[3]

I have not gone into equipment safety grounding aspect of safety grounding primarily because if one follows the advice in the references, it will be covered adequately for commercial equipment build after the 1980’s. However, if you are using home brew (ham speak for home made) equipment or equipment built before 1980 you should assure that metal cases are grounded properly[4]. Failure to do so could result in fatal electrical shock.

[1] - Lightning and Atmospheric Electricity Research at GHCC This is a very informative but somewhat technical.

[2] - House ground layouts This reference is recommended by ARRL as a practical approach to the problem.

[3] - See posting “Radio Frequency Ground”

[4] - Grounding for this type of equipment must be handled on a case by case basis so I will make not recommendations along this line. It is up to the user to become informed on the hazards and how to mitigate such hazards.

Station Grounding: An Introduction

2012-01-15T07:47:00.000-08:00

Properly grounding a radio station is far more important than is usually discussed in most ham radio license classes. A number of problems may arise from a lack of, improper, or poor grounding. First, there are two kinds of grounding to be managed in a radio station, signal ground and safety ground. These are not one and the same, but they are integral parts essential parts of any station installation. This discussion will not go into detail of grounding techniques. It will discuss, however briefly, some things that may result from grounding problems.

First, Safety Ground

There are two aspects to safety ground. Most importantly it protects you, your house, and others from electrical shock or possible fire due to faulty equipment. It provides the path by which fuses are blown should a dangerous condition occur in any piece of electrical equipment. Secondly, it provides a path to dissipate high voltage that may happen due to a lightning event. Notice I did not say lightning strike. In truth there is almost nothing one can do to prevent damage from a direct lightning strike. The best we can hope to do is mitigate the circumstances that lead to a lightning strike. In other words we make high objects less attractive to lightning by providing pathways to dissipate static electricity to ground before it can build to critical levels.

Second, Radio Frequency Ground

Turns out RF ground can be much more complicated to manage than safety ground. However, the lack of or a poor safety ground can almost assure that a station will have RF ground problems. This is particularly but not exclusively true to frequencies below 30 MHz. So what are some of the problems you may encounter?

You may have or develop RF in the shack. That is a condition where the metal surfaces of some or all of your equipment may exhibit radio frequency radiation. This is most often noticed when you touch the metal parts of your station equipment and get a RF burn or at least it feels hot as in temperature not an electrical shock. In less severe cases you may notice that your SWR changes when you touch the station equipment. In fact you may not even have to come in direct contact to see the SWR fluctuate some. Another indication is you may have someone tell you that your audio sounds bad or is poor quality[1]. It may show up as a buzz or distortion. RF in the shack can manifest in a number of ways, but the ones listed are the most common. In any case RF in the shack is to be avoided.

Details and references to help with grounding issues will come in other postings found under the Grounding label on this blog.

ARRL has a number of references that can be reach by starting with this link. http://www.arrl.org/grounding-q-a

[1] - On VHF/UHF a condition called multipath may also cause very poor or unreadable audio. However, this condition will cause both your transmitted and received signals to sound bad. And it usually only happens in a single direction. Other stations in different directions will be just fine.

Feed Line: Introduction to coax

2012-01-11T15:24:00.000-08:00

Two rules to keep in mind. One, keep it as short as practical. And two, buy the best quality your budget will afford.

I’ve heard a number of new hams ask, “What kind of coax should I buy?”

First, for almost any ham antenna, 50 Ohm coax is about the only requirement. The next consideration is loss. The very lowest loss type of coax, usually called “hard line”, is extremely expensive while higher loss small diameter coax is less expensive. Generally speaking, larger the diameter coax is the lower loss. The amount of loss also changes with the type of insulating material between the outer conductor (shield) and the center conductor. This is taken into account on coax loss specification tables.

However, the greatest contributor to coaxial line loss is frequency of operation.

Here are a couple of loss tables for some common 50 Ohm coax.

This one is for Belden 9258 (RG-8x) which is .242 inch diameter. Belden is a cable manufacture.

Frequency (MHz) Nom. Attenuation (dB/100 ft.)

1 0.3

10 0 .9

50 2.1

100 3.1

200 4.5

400 6.6

700 9.1

900 10.7

1000 11.2

This one is for Belden 8214 (RG-8/U) which is .403 inch diameter.

Frequency (MHz) Nom. Attenuation (dB/100 ft.)

1 0 .1

10 0.5

50 1.2

100 1.7

200 2.6

400 3.9

700 5.6

900 6.5

1000 7.0

Note that RG-8x is about half as big around as RG-8. But RG-8 has about half the loss at all frequencies. Because of the weight and flexibility differences, RG-8 is used mostly for home installations while RG-8x is a good choice for portable operations.

Follow this link to an abbreviated table for most coax types. http://rfcafe.com/references/electrical/coax-chart.htm

For RG-8x see. http://www.dxengineering.com/pdf/Belden%20RG8X%20Date%209258.pdf This is a complete specification.

If you already have the coax, check it carefully for the manufacture and numbers printed on the outer cover. Try a Google search with the manufacture name and numbers, at least type in the RG type followed by the word spec. You may have to look at a number of “hits” to find what you’re looking for. Don’t give up easily.

SWR: Coax Check

2012-01-07T10:34:00.000-08:00

Even a new coaxial cable should be checked. The coax and connectors may look flawless, check fine with an Ohm meter and still have a serious mismatch, i.e. high SWR.

You will need a 50 Ohm dummy load, a SWR meter, a known good coax jumper, Ohm meter, and transmitter.

Ohm meter tests:

Check the cable from the center pin on one connector to the center pin of the connector on the other end. These should be a short circuit, less than one ohm[1]. Next check the shield from the outside of one connector to the other. This should also be a short circuit. Now check from the center pin to the shield using either connector. This should be an open circuit, no reading, on the highest Ohms scale[2]. Be sure that you are not measuring you fingers by coming in contact with the meter probe tips or any part of the connectors when you make this measurement. Stay off the metal. When these checks have been made and the connection are all correct you may proceed to the SWR check.

SWR meter tests:

Connect the dummy load to one end of the coax you want to test. Connect the other end of the coax to the Antenna connection on the SWR meter. Connect the jumper to the Transmitter connection on the SWR meter. Connect the other end of the jumper to the transmitter’s output connector.

Turn the transmitter power to minimum and set the mode to CW, AM or FM. SSB will not work. Now transmit and read the SWR. It should be no more than 1.1 to 1 at the frequency that you intend to use the coax.

If the SWR is higher, carefully do a visual check of the connectors and run the Ohm meter test while wiggling the connectors. This is especially true for a home build coaxial cable. It is very easy to short coax when installing connectors of any type. A cable may not be shorted or open but still have SWR problems.

[1] - 75 feet of RB-8x measured 0.6 Ohms on both the shield and the center conductor. When the leads are shorted, they measure 0.3 Ohms. That means the coax is 0.3 Ohms. This is acceptable

[2] - The meter I use has a 20 MOhm scale. It has no reading on the same piece of coax. This is fine. You can check the meter by wetting a finger on each hand and measuring your resistance to assure that the meter is working. This reading will vary widely and will even change depending on how tightly you hold the meter lead tips.