Categories: Radio

Three Stage 9V FM Transmitter

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 (there are two version available):
[wpdm_file id=45]

circuit diagram

View Comments

Recent Posts

Guitar Synthesizer Schematic Diagram Collection

Guitar Synthesizer Schematic Diagram In this post, we provide a collection of schematic diagrams of…

54 years ago

Handy Talky HT DIY Schematic Diagram

Handy Talky Schematic Diagram This is an old electronic scheme of the Handy Talky (HT)…

54 years ago

Doorbell Ringer Birdie Tone

This is an old or "very old" schematic diagram of birdie tone or sound generator.…

54 years ago

200W MOSFET Amplifier based IRFP250N

Here is the 200W MOSFET amplifier powered based on four piece of IRFP250N, they are…

54 years ago

300W RMS Stereo Power Amplifier based IC TDA7294

This is the 300W RMS stereo power amplifier circuit project. This amplifier is based four…

54 years ago

Stereo Tone Control with Line In + Microphone Mixer

This is an active stereo tone control circuit using very well known op-amp IC of…

54 years ago