elektroblog

3 watt FM Transmitter

noreply@blogger.com (fikriblog) — Sun, 4 Dec 2011 21:44:00 -0800

This is the schematic for an FM transmitter with 3 to 3.5 W output power that can be used between 90 and 110 MHz. Although the stability isn't so bad, a PLL can be used on this circuit. This is a circuit that I've build a few years ago for a friend, who used it in combination with the BLY88 amplifier to obtain 20 W output power. From the notes that I made at the original schematic, it worked fine with a SWR of 1 : 1.05 (quite normal at my place with my antenna)

Part	Total Qty.	Description	Substitutions
R1,R4,R14,R15	4	10K 1/4W Resistor
R2,R3	2	22K 1/4W Resistor
R5,R13	2	3.9K 1/4W Resistor
R6,R11	2	680 Ohm 1/4W Resistor
R7	1	150 Ohm 1/4W Resistor
R8,R12	2	100 Ohm 1/4W Resistor
R9	1	68 Ohm 1/4W Resistor
R10	1	6.8K 1/4W Resistor
C1	1	4.7pF Ceramic Disc Capacitor
C2,C3,C4,C5,C7,C11,C12	7	100nF Ceramic Disc Capacitor
C6,C9,C10	3	10nF Ceramic Disc Capacitor
C8,C14	2	60pF Trimmer Capacitor
C13	1	82pF Ceramic Disc Capacitor
C15	1	27pF Ceramic Disc Capacitor
C16	1	22pF Ceramic Disc Capacitor
C17	1	10uF 25V Electrolytic Capacitor
C18	1	33pF Ceramic Disc Capacitor
C19	1	18pF Ceramic Disc Capacitor
C20	1	12pF Ceramic Disc Capacitor
C21,C22,C23,C24	4	40pF Trimmer Capacitor
C25	1	5pF Ceramic Disc Capacitor
L1	1	5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm
L2,L3,L5,L7,L9	5	6-hole Ferroxcube Wide band HF Choke (5 WDG)
L4,L6,L8	3	1.5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm
L10	1	8 WDG, Dia 5 mm, 1 mm CuAg, Space 1 mm
D1	1	BB405	BB102 or equal (most varicaps with C = 2-20 pF [approx.] will do)
Q1	1	2N3866
Q2,Q4	2	2N2219A
Q3	1	BF115
Q5	1	2N3553
U1	1	7810 Regulator
MIC	1	Electret Microphone
MISC	1	PC Board, Wire For Antenna, Heatsinks

Note:

Email Rae XL Tkacik with questions, comments, etc.
The circuit has been tested on a normal RF-testing breadboard (with one side copper). Make some connections between the two sides. Build the transmitter in a RF-proof casing, use good connectors and cable, make a shielding between the different stages, and be aware of all the other RF rules of building.
Q1 and Q5 should be cooled with a heat sink. The case-pin of Q4 should be grounded.
C24 is for the frequency adjustment. The other trimmers must be adjusted to maximum output power with minimum SWR and input current.
Local laws in some states, provinces or countries may prohibit the operation of this transmitter. Check with the local authorities.

source :http://www.aaroncake.net

Low Voltage Alarm

noreply@blogger.com (fikriblog) — Sun, 4 Dec 2011 20:53:00 -0800

This low voltage circuit can be used to monitor batteries and other volatile sources of current for problems. The circuit sounds an alarm and lights an LED, but can be interfaced to any number of other circuits for many different uses.

Part	Total Qty.	Description	Substitutions
R1, R3	2	1K 1/4W Resistor
R2	1	5K Pot
U1	1	LM339 Op Amp IC
D1	1	1N5233B Zener Diode
D2	1	LED
BZ1	1	Piezo Buzzer
MISC	1	Board, wire, socket for IC

Note :

The circuit will operate from 9V to 12V.
Adjust R2 until the alarm goes off at the correct voltage.

Air Flow Detector

noreply@blogger.com (fikriblog) — Sun, 4 Dec 2011 20:50:00 -0800

This simple circuit uses an incandescent lamp to detect airflow. With the filament exposed to air, a constant current source is used to slightly heat the filament. As it is heated, the resistance increases. As air flows over the filament it cools down, thus lowering it's resistance. A comparator is used to detect this difference and light an LED. With a few changes, the circuit can be connected to a meter or ADC to provide an estimation on the amount of air flow.

Part :

Part	Total Qty.	Description	Substitutions
R1	1	100 Ohm 1/4W Resistor
R2	1	470 Ohm 1/4W Resistor
R3	1	10k 1/4W Resistor
R4	1	100K 1/4W Resistor
R5	1	1K 1/4W Resistor
C1	1	47uF Electrolytic Capacitor
U1	1	78L05 Voltage Regulator
U2	1	LM339 Op Amp
L1	1	#47 Incandescent lamp with glass removed (See "Notes")
D1	1	LED
MISC	1	Board, Wire, Sockets for ICs, etc.

Notes :
The glass will have to be removed from L1 without breaking the filament. Wrap the glass in masking tape and it in a vise. Slowly crank down until the glass breaks, then remove the bulb and carefully peel back the tape. If the filament has broken, you will need another lamp.
Source : my electronic