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
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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