How do you build a BFO for a shortwave Radio?

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.

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framistan4 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.
Graydant (author)  framistan4 years ago
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 ?
Graydant (author)  steveastrouk4 years ago
Yes. I'd like to be able to.
EI4GOB Graydant2 years ago

Good for you! If you still have to learn Morse code then this Windows program by Ray Goff G4FON is the best way in my opinion.

73 Fionnbarra EI4GOB

delta89414 years ago
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: