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Need circuit for audio transciever.

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DexterLB

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Hello. I want to make an audio transceiver on 27MHz. Frequency-modulation (FM) would be better, but I think 27MHz is too low. I can't use any other frequency because in Bulgaria it's forbidden. So, I am looking for simple circuits of an audio transmitter and receiver. I will use standard computer line-out voltage for the audio input on the transmitter and a 0.7W 8Ω speaker on the receiver side. I would appreciate any help in finding the perfect circuits :)
 
Nearly 100 years ago CB radios used 27MHz.
I don't think anybody uses CB radios anymore.
Look in Google for CB radio Circuit.
 
Hello. I want to make an audio transceiver on 27MHz. Frequency-modulation (FM) would be better, but I think 27MHz is too low. I can't use any other frequency because in Bulgaria it's forbidden. So, I am looking for simple circuits of an audio transmitter and receiver. I will use standard computer line-out voltage for the audio input on the transmitter and a 0.7W 8Ω speaker on the receiver side. I would appreciate any help in finding the perfect circuits :)


For the receiver, you can do it with one IC such as this one:
**broken link removed**

Check out figure 4 on page 7 for a schematic. Your input will not be 45 MHz so you will have to change the local oscillator crystal frequency to suit your channel.

This IC, or one of its brothers including all SA606 through SA676 are able to do this job. One or another are usually available through most suppliers.

For your transmitter, you can use one of several simple one-chip communication transmitter ICs. One example is the MC2833, although I think this is an old part and maybe hard to get. I see it is available at Ocean State Electronics. Experienced builders of small transmitters often use designs with a few transistors instead of an IC. This may be too difficult for you, but there are many examples at VHF frequencies that you can copy and adjust to 27 MHz. There are a few here:
**broken link removed**
 
There's no way of getting any of these two ICs here. But that site you posted, it has wonderful circuits. These two are perfect:
**broken link removed** (Receiver)
**broken link removed** (Transmitter)

But the text says they work above 70MHz, so it needs converting.
Do I only need to put a 27MHz crystal to make the circuits work on 27MHz or I should change other component values too?

Also, I should just remove the microphone and the trimmer and put a regular audio jack, right?

As for the difficulty... making the circuit is the most difficult part. Then I'll design the PCB in Proteus ARES and make it using the "Laser Iron" method. I also have all the components for those two circuits, except the 455KHz filter. And I don't know where to get the two ceramic filters from to make it. I've been googling on SFG455A3 but found nothing. Do you know something similar or an equivalent?
 
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