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Written by Hans Summers   
Saturday, 11 July 2009 10:28

IF transformer version

Here's a BFO circuit by Jim G4NWJ. He writes: "This is the BFO circuit that I have installed in my radios, I have used the Hi/Lo tone switch to provide the negative line and tapped into the positive supply on the right hand side of the circuit board. There is room to tuck the unit, which I assembled "ugly bug style", under the board but you really need to use the 5 or 7mm I. F. transformer cans because some of the radios have insufficient space to accommodate the 10mm size. I taped a short length of wire from the output across the back of the circuit board and then adjusted the slug to give me the correct note. This I found easier that trying to set it up with the frequency meter. I will try to get some photographs off to Hans in the next day or so but life has been hectic over this weekend. There are plenty of other circuits which could be used including those with 455 kc resonators but which ever you chose remember space is at a premium."

Ceramic resonator version

Here's Jim's Mk2 version which uses a ceramic resonator (Click for full size image). It fits under the radio in the middle of the PCB allowing the batteries to sit undisturbed in their holder. It needs only the minimum of BFO injection in order not to de-sensitise the radio.

 
 
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