Electronic – FM Radio transmitter and receiver circuits


I'm planning on building a FM transmitter and receiver circuit for an electronics project. I was just wondering if these two circuits would work together. Also would they be suitable for transmitting and receiving audio?

The transmitter circuit uses the ba1404 chip, link to circuit info here:

The receiver circuit can be found here:

Any other advice would gratefull

Best Answer

The BA1404 does transmit audio, in stereo.

Whether they are suitable for use together depends on the frequency you use; on whether the receiver circuit will handle the +/-75kHz modulation that the BA1404 will do to the carrier; whether it uses the same time constant for de-emphasis that the transmitter uses for pre-emphasis; whether has a stereo decoder; and of course on whether they are located close enough together for the power of the transmitter to excite the sensitivity of the receiver.

NB The link is incorrect in saying that C13/14 are part of the pre-emphasis circuit. They aren't. It is a simple RC high-pass formed by R6/C15 and R7/C16 respectively. These values will give you 50uS pre-emphasis.

As the receiver is built for 88-108MHz I think it is safe to assume it will handle the modulation, but I don't see any stereo decoder in the receiver circuit. So the answer is 'no' unless you arrange to broadcast in mono, by killing the 19kHz pilot tone in the transmitter, or append a suitable decoder, e.g. the one at http://www.fmmpx.com, which I've built many times for modernising several brands and models of FM tuner.

I would add that the receiver looks pretty basic. I would expect high distortion and poor stereo if any. There are better circuits around. Indeed you don't even need one: just use an old FM tuner. This one talks about component numbers in the text but doesn't show them in the schematic, which isn't too encouraging.