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3W FM Transmitter

The document provides schematics and parts lists for two FM transmitters: a 3W transmitter operating between 90 and 110 MHz and an FM telephone bug that transmits phone line audio. The 3W transmitter can be enhanced with a PLL for stability and has been tested with a BLY88 amplifier for higher output. The FM telephone bug is a beginner-friendly project that transmits audio from a phone line to FM radios within a 200-foot range, tunable from 88 to 94 MHz.

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taufiq
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31 views2 pages

3W FM Transmitter

The document provides schematics and parts lists for two FM transmitters: a 3W transmitter operating between 90 and 110 MHz and an FM telephone bug that transmits phone line audio. The 3W transmitter can be enhanced with a PLL for stability and has been tested with a BLY88 amplifier for higher output. The FM telephone bug is a beginner-friendly project that transmits audio from a phone line to FM radios within a 200-foot range, tunable from 88 to 94 MHz.

Uploaded by

taufiq
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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P170.

3W FM Transmitter
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).

Circuit diagram

Parts:
R1,R4,R14,R15 10K 1/4W Resistor
R2,R3 22K 1/4W Resistor
R5,R13 3.9K 1/4W Resistor
R6,R11 680 Ohm 1/4W Resistor
R7 150 Ohm 1/4W Resistor
R8,R12 100 Ohm 1/4W Resistor
R9 68 Ohm 1/4W Resistor
R10 6.8K 1/4W Resistor
C1 4.7pF Ceramic Disc Capacitor
C2,C3,C4,C5,C7,C11,C12 100nF Ceramic Disc Capacitor
C6,C9,C10 10nF Ceramic Disc Capacitor
C8,C14 60pF Trimmer Capacitor
C13 82pF Ceramic Disc Capacitor
C15 27pF Ceramic Disc Capacitor

290
C16 22pF Ceramic Disc Capacitor
C17 10uF 25V Electrolytic Capacitor
C18 33pF Ceramic Disc Capacitor
C19 18pF Ceramic Disc Capacitor
C20 12pF Ceramic Disc Capacitor
C21,C22,C23,C24 40pF Trimmer Capacitor
C25 5pF Ceramic Disc Capacitor
L1 5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm
L2,L3,L5,L7,L9 6-hole Ferroxcube Wide band HF Choke (5 WDG)
L4,L6,L8 1.5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm
L10 8 WDG, Dia 5 mm, 1 mm CuAg, Space 1 mm
D1 BB405 or BB102 or equal (most varicaps with C = 2-20 pF [approx.] will do)
Q1 2N3866
Q2,Q4 2N2219A
Q3 BF115
Q5 2N3553
U1 7810 Regulator
MIC Electret Microphone
MISC PC Board, Wire For Antenna, Heatsinks

Notes:
1. Email Rae XL Tkacik with questions, comments, etc.
2. 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.
3. Q1 and Q5 should be cooled with a heat sink. The case-pin of Q4 should be grounded.
4. C24 is for the frequency adjustment. The other trimmers must be adjusted to maximum output power
with minimum SWR and input current.
5. Local laws in some states, provinces or countries may prohibit the operation of this transmitter. Check
with the local authorities.

P171. FM Telephone Bug


Here is a simple transmitter that when connected to a phone line, will transmit anything on that line
(execpt the dial tone) to any FM radio. The frequency can be tuned from 88 to about 94Mhz and the range
is about 200 feet. It is extremely easy to build and is therefore a good, useful beginner project.

Circuit diagram

Parts
R1 180 Ohm 1/4 W Resistor
R2 12K 1/4 W Resistor
C1 330pF Capacitor
C2 12pF Capacitor
C3 471pF Capacitor
C4 22pF Capacitor
Q1 2SA933 Transistor
291

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