Re: Selecting the correct BFO frequency

Kerr Smith

Thanks for the replies - will adjust the BFO so it sits at 20dB down the edge of the filter - I will try lowering its frequency first and see how it goes, I tried changing the capacitance in series with the crystal as a quick test and this did alter its frequency so I will look in to this more tomorrow.

The circuit for the BFO I am using is the one shown in figure 18 of the following site:

This receiver is planned to be a completely handmade version - my last creation was a Bitx20 using a si5351 and this works very well, it has a display screen, rotary encoder tuning as well as memory - I spent far longer on writing the software than in making the actual circuit (every time I thought I was finished I had another idea for an extra feature).

For this receiver I am trying to design it as much as possible by hand so I can learn more about how to do this. I only have a few bits left such as the second mixer, another RF amplifier and the audio amplifier - I already have working versions of the mixer and tuned RF amplifier so these just need duplicating.

Just to clarify - will it matter if I decide to put the BFO above or below the center frequency of the crystal filter - this is just going to be a receiver for 40m, there will be no transmitting circuits?

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