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.
Schematic
This is the schematic of the phone transmitter
Parts
Part
Total Qty.
Description
Substitutions
R1 1 180 Ohm 1/4 W Resistor
R2 1 12K 1/4 W Resistor
C1 1 330pF Capacitor
C2 1 12pF Capacitor
C3 1 471pF Capacitor
C4 1 22pF Capacitor
Q1 1 2SA933 Transistor
D1, D2, D3, D4 4 1SS119 Silicon Diode
D5 1 Red LED
S1 1 SPDT Switch
L1 1 Tuning Coil
MISC 1 Wire, Circuit Board
Notes
1. L1 is 7 turns of 22 AWG wire wound on a 9/64 drill bit. You may need to experiment with the number of turns.
2. By stretching and compressing the coils of L1, you can change the frequency of the transmitter. The min frequency is about 88 Mhz, while the max frequency is around 94 Mhz.
3. The green wire from the phone line goes to IN1. The red wire from the phone line goes to IN2. The green wire from OUT1 goes to the phone(s), as well as the red wire from OUT2.
4. The antenna is a piece of thin (22 AWG) wire about 5 inches long.
5. All capacitors are rated for 250V or greater.
6. The transmitter is powered by the phone line and is on only when the phone is in use. S1 can be used to turn the transmitter off if it is not needed.
7. If you have problems with the LED burning out, then add a 300 ohm 1/4W resistor in series with it.
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Saturday, January 23, 2010
3 Watt FM Transmitter
3 Watt FM Transmitter
By Rae XL Tkacik
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).
Schematic
This is the schematic of the 3W FM Transmitter
Parts:
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
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.
Back To Circuits Page | Mail Me | Search
Schematic This is the schematic of the 3W FM Transmitter
By Rae XL Tkacik
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).
Schematic
This is the schematic of the 3W FM Transmitter
Parts:
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
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.
Back To Circuits Page | Mail Me | Search
Schematic This is the schematic of the 3W FM Transmitter
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