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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: http://www.circuitstoday.com/stereo-fm-transmitter-using-ba1404

The receiver circuit can be found here: http://circuits-projects.blogspot.co.uk/2014/07/simple-and-mini-fm-receiver.html

Any other advice would gratefull

Darth Vader
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  • Here is a very simple digital receiver, low-cost and small enough to mount on a small speaker. Runs from USB power. https://electronics.stackexchange.com/questions/306497/single-station-fm-radio/306535#306535 – SDsolar Nov 01 '17 at 02:42

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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.

user207421
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  • Could you recommend a receiver circuit to use with the ba1404 circuit? – Darth Vader Sep 08 '14 at 15:32
  • Well, what are your requirements? Audio? Stereo? How much bandwidth? How much distortion? How much dynamic range? How sensitive? How selective? – user207421 Sep 08 '14 at 22:14
  • Audio, far amount of bandwith, not much distortion, a reciever circuit that is going to pick up audio transmitted by the ba1404 and output audio clearly to headphones. Also how good is the range with the ba1404 circuit? – Darth Vader Sep 09 '14 at 16:59
  • That circuit has very low output. It's usual to run it into a FET to amplify the final output to a milliwatt or so. Beware of the FCC regulations on this. Do you have to design it yourself? You can build both items from kits for about $100 from ramseyelectronics.com. – user207421 Sep 10 '14 at 02:15
  • I do not have to design the circuit but I am not allowed to use kits either. Is there a circuit I can use that will receive FM from the ba1404 circuit and turn it into audio? Just as a side note both the circuits need to run on no more than 50V. -Thanks again – Darth Vader Sep 10 '14 at 16:48
  • Again it still depends on what you mean by 'not much'. Also on how much range you need, in yards or metres. There are plenty of schematics on the Web, I can't really recommend one over the other, but I would be looking for one with a recognizable IF strip and discriminator, also audio filtering to get rid of the 19kHz stereo pilot, the 38kHz MPX switching frequency and its harmonics, all the 23-53kHz stereo difference signal, 67kHz SCA signal, etc. Why can't you use a kit? – user207421 Sep 11 '14 at 07:26
  • I'm building the FM transmitter and receiver as part of an electronics project which will count towards a qualification in electronics. So we are not allowed to use kits. If you could recommend two relatively simple FM transmitter and receiver circuits that work together that would be great. I don't need a massive range either. Do you think Bluetooth would be a good option? Thanks for the help – Darth Vader Sep 11 '14 at 17:06
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    Hang on. FM transmits over the air by frequency-modulating a VHF carrier. Bluetooth is a completely different kettle of fish. The BA1401 circuit is OK as is. So is the other one for homework. Just disable the 38kHz oscillator in the transmitter and site them pretty close together with suitable aerials. A normal 4 foot whip will do in both cases. – user207421 Sep 12 '14 at 01:17
  • So your solution is to remove the crystal from the ba1404 circuit? And as long as I use a receiver circuit that can receive FM at the same frequency as the transmitter, I should be good to go with the two circuits I listed in my original question? Thanks for the help I really appreciate it – Darth Vader Sep 12 '14 at 16:35
  • Receiver circuit: https://electronics.stackexchange.com/questions/306497/single-station-fm-radio/306535#306535 – SDsolar May 21 '17 at 01:24