Re: Full-Range IF Selectivity; The Hammarlund Variable Crystal Filter
It's still work in progress. The gear is in the shed at the end of the garden. It's winter and the garden is wet...and it's Christmas.
Instead I'm doing thought experiments to work out the best way of measuring the response of the filter / IFT matching before putting it in an actual receiver.
The present favourite is to let an oscilloscope imitate the 1st IF Amp Valve (the 30pF of scope input capacitance ought to be subtractable from the IFT tuning capacitance) while feeding it from a sig gen with ~2k series resistor as the source. Once the bandwidth and ripple look OK, meaning it's terminated right, then proceed with the input matching from the mixer anode. Not sure how far down the skirts it will be possible to see using the scope. I would hope that -20dB should be possible. The only working scope is a Telequipment D61a.
Last edited by Jon_G4MDC; 31st Dec 2022 at 11:24 am.
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