9V FM Radio Transmitter circuit diagram

Here the simple and low cost FM transmitter circuit. The frequency range of this FM transmitter should be about 89MHz – 109MHz. Output power is about 9mW at 9V.

R1,R6_____________________12K R2,R4_____________________100K R3________________________22K R5________________________1K R7________________________100R Q1________________________BC338 Q2________________________BC548B Microphone JinIn ECM-60P B1

C1___________________10uF/25V C2___________________22n C3___________________10n C4___________________3n3 C5___________________2p7 C6___________________22p C7___________________100uF/16V tuning capacitor_____0-30pF

Download the complete explanation of this FM Transmitter (include circuit diagram, component list, the circuit’s work) in PDF format HERE

FM Transmitter with 2 Transistors circuit diagram

Here the simple and cheap FM transmitter which powered using two transistors. This circuit may be tuned to operate over the range 87-108MHz with a range of 20 or 30 metres.

The coil L1 was consist of 7 turns on a quarter inch plastic former with a tuning slug. The tuning slug is adjusted to tune the transmitter. Actual range on this prototype tuned from 70MHz to around 120MHz. The aerial is a few inches of wire. Lengths of wire greater than 2 feet may damp oscillations and not allow the circuit to work.
Although RF circuits are best constructed on a PCB, you can get away with veroboard, keep all leads short, and break tracks at appropriate points.
One final point, don’t hold the circuit in your hand and try to speak. Body capacitance is equivalent to a 200pF capacitor shunted to earth, damping all oscillations.

1.5 Watt FM Transmitter circuit diagram

This is 1.5 Watt FM Transmitter circuit. This circuit should be able to cover 1-2 KM range.

Components List

R1=220K R2=4.7K R3,R4=10K R5=100ohm

C1,C2=4.7uF Electrolytic C3,C4=1nF C5=2-15pF C6=3.3pF

Q1=BC547C Q2=2N2219A P1=25K MIC=Electret Condenser Type

P1 act as condenser microphone volume level. For FM, coil will be small. Use thin gauge enamel magnet wire. the diameter of coil will be a couple mm: use ink tube from pen to form, and try 8-12 turns. Small inductance coils make for much guess work.

Three Stage 9V FM Transmitter circuit diagram

This circuit is a powerful three stage, 9V FM transmitter (Tx) with a range of up to 1 kilometer in the open. It uses an RF transistor in its output stage and two BC547’s for the first two stages. Distance of trans-mission is critically dependent on the operating Conditions (in a building or out on the open), type of aerial used (single wire or dipole), operating voltage (12V is better than 6V) and if the circuit is peaked for maximum performance.

Components List:

Resistors, 5%, 1/4W: 100R 1 470R 1 4K7 1 22K 1 39K 1 47K 2 1M 1

Capacitors: Trim cap 5-20pF, red – 1 5.6 pF ceramic – 1 10p ceramic – 2 47pF ceramic – 3 1nF ceramic – 1 20nF or 22nF ceramic – 2 100nF monoblock – 2

RF transistor ZTX320 – 1 Small signal transistor BC547 – 2 6 turn tinned copper coil – 1 6 turn enamelled coil – 1 8 turn enamelled coil – 1 9V battery snap – 1 Electret microphone – 1 PCB-mounted SPDT switch – 1 Antenna wire 1.6m

The circuit is basically a radio frequency (RF) oscillator that operates around 100 MHz. Audio picked up and amplified by the electret microphone is fed into the audio amplifier stage built around the first transistor. Output from the collector is fed into the base of the second transistor where it modulates the resonant frequency of the tank circuit (L1 coil and the red trimcap) by varying the junction capacitance of the transistor. Junction capacitance is a function of the potential difference applied to the base of the transistor T2. The tank circuit is connected in a Hartley oscillator circuit. The final stage built around T3 amplifies the output RF signal.
Download the complete manual and explanation in PDF version HERE