On Sat, 19 Jul 2014, dave wrote:


3580KHz is the 80m psk band

I think that was deliberate, the crystals were there, so they picked that
frequency (though likely risked competition for that frequency from others
that could take advantage of the cheap crystals).

If you pick a frequency with a cheap crystal, you can build a direct
conversion receiver using a ladder filter, the antenna feeds an amplifier
which feeds the crystal filter, then more amplification and the product
detector. Very neat, but of course not tuneable at all.

Michael