Easy and reliable BFO
designed by sv3ora


This BFO can be used to allow SSB reception on those cheap shortwave radios that have 455KHz IF. It is a 455KHz oscillator that is inserted inside the radio and beats with the IF signal to produce detectable CW or voice. It uses a 455KHz IF transformer salvaged of an older radio and it has only four components.

Here is the Schematix data for the BFO.

cq455khz crtrans csformer dpit dqea drea dsea dtii elit emea enea eoea epve eqei erii esit etve fk22pf flse fn0v7 fots fpve fqbi frse fssv ftae glie gmeh gnea goei gpve gqen grti gsis gtve hlae hm1meg hoae hpis  hqea hrea hsea htti ilis imea inea ione ip2n2222 joee

The BFO can operate at voltage as low as 0.7v, which makes it suitable for those 3v powered portable radios. The harmonics content is very low, as these are well filtered by the collector tuned circuit. Almost any BJT type can be used at that low frequency. The BFO is left unconnected from the rest of the radio, as it's signal leaks to the nearby circuits. However, if you want you can connect the output side of the transformer to the GND from one side and to the circuit of interest on the other side, through a small ceramic capacitor.

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