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How do you build a BFO for a shortwave Radio? Answered

I was on amazon looking to buy a better shortwave radio and this guy on there said "I did build a separate little circuit called a bfo. When I hold this next to the radio, I can understand radio amateur transmissions (around 7 mHz). " and I would very much like to be able to do the same, So how would you build such a thing. Thank You. All the best.



Best Answer 4 years ago

BFO just means a "Beat-Frequency-Oscillator".... It's just an oscillator. In ham radio, when morse code is sent, it is just a simple carrier frequency with no modulation. If you tune in to it, it just sounds like someone keying up a mic and not saying anything. When you bring an oscillator tuned 1000 hertz higher or lower than their transmission, you hear the difference in the 2 frequencies... so you hear the tone. I think this works for ssb single-sideband transmissions as well. Most good shortwave radio receivers have a switch to turn ON and OFF the BFO. It is not needed on standard AM or FM transmissions.

That explains it, and one my radio's has such a switch but I never knew what it was for, Now I don't need to just buy another radio for it. lol

I'm still new to shortwave, have only had my two SW radio's for a year. I'm going buy a better radio still but haven't decided I'll look for that to be on it. Thank You..

Why ? Are you actually trying to listen to morse ?

If you want a nice sensitive and portable HF receiver try the Grundig G3. This radio has the ability to listen to SSB modulated signals. If you like to try your hand at building a BFO circuit here are a few good easy projects. With these you can turn almost any department store AM/FM receiver into a HF receiver; provided you detune the radio and get it into the correct band of frequencies first!



(This is a better circuit. A 160pF variable capacitor is needed from an old AM/FM radio, the IF transformer is NOT needed, buy a few 455khz ceramic resonators from ebay, for the JFET anything can be used, J310, 2N3819 etc)

This pages contains a very simple HF receiver circuit: