Hi Greg

 GM> If I can remember the Yasue FRG-7, or possibly I'm
 GM> thinking of another receiver from that era, the signal went
 GM> through a fixed 30MHz low pass filter then to a (diode?) mixer
 GM> stage where it was heterodyned up to about 70MHz. Most of the
 GM> gain was in the 70MHz IF strip, IIRC.

 GM> The way they generated the local oscillator signal was quite
 GM> ingenious, but quite beyond my powers to remember or work it
 GM> out now -- I wish I'd taken a copy of the circuit.

I've still got one of those. If you want a copy of the circuit I'll
happily scan it in for you.

It uses a 'Wadley Loop' to receive up to 30MHz in 1MHz bands.
The first local osc (55.5-84.5MHz) selects the band. It mixes the
desired RF up to 55MHz.

The 1st IF amp has a 1MHz bandwidth and feeds the 2nd mixer.

A 1MHz crystal oscillator with loads of distortion produces a comb
of harmonics. The 1st LO is mixed with this comb and a bandpass
filter picks out the product at 52.5MHz.

This signal feeds the other input to the 2nd mixer to produce the
2nd IF (2-3MHz). Errors in the 1st LO are cancelled.

The signal is now mixed down to 455kHz with a 3rd LO of between
2.455-3.455MHz which is the main tuning dial.

Bye for now

Tony
 
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