Saturday, April 16, 2011

Coilless FM transmitter !

 If you are in the problem to make perfect coils for FM Transmitter then this is your time to go on..... See this coil less and easy FM Transmitter.

The RF oscillator using the inverter N2 and 10.7Mhz ceramic filter is driving the parallel combination of N4 to N6 through N3.

Since these inverters are in parallel the output impedance will be low so that it can directly drive an aerial of 1/4th wavelength. Since the output of N4-N6 is square wave there will be a lot of harmonics in it. The 9th harmonics of 10.7Mhz (96.3Mhz) will hence be at the center of the FM band .
N1 is working as an audio amplifier. The audio signals from the microphone are amplified and fed to the varycap diode. The signal varies the capacitance of the varycap and hence varies the oscillator frequency which produce Frequency Modulation.

1 km. FM Transmitter


This one is a high power long range (use yagi antenna)  FM Transmitter  that provides very good frequency stability in about 1km range and very good microphone sensitivity. It can be used inside guitars, as a part of remote control systems or in other similar applications.

The features said above are achieved by including an RF amplifier stage with 10dB gain and AF preamplifier stage to boost the modulation.

The circuit construction is simple. L1 is integrated into the PCB with 3.25 turns. Transistors are not critical. The BC547s can be replaced with any small signal NPN type transistor and BC557 is a general purpose PNP transistor so it can also be replaced easily.

The power consumption is low. The finished circuit draws about 30mA. A single 9V battery is ample to power the FM wireless microphone.

The PCB file is given in the download section of the project page. You should check Harry's page for more detailed information about the components, PCB modifications and the other features of the circuit.

if you need more details then post a comment below