On Thursday 03 May 2007 21:29:00 Lyle Johnson wrote: > In the olden days, analog radios would use two IF filters and slide them > back and forth against each other to form variable bandwidth filters.
Yes indeed. My Eddystone EA12 receiver that I bought from Tom Roberts, G3YTO (SK 1985) is a dual conversion with a tunable first IF from 1.1 Mc/s to 1.7 Mc/s and crystal controlled converters changing the bands to the tunable IF. The second IF is 100 kc/s with a slot filter and continuously variable selectivity: this is accomplished by varying, mechanically the coupling between the coils - it's like flying by the seat .. rather than by wire. At the narrow end of the filter, a 100 kc/s crystal kicks in and I can feel the switch that does it. With up to volts input to the linear ECC189 to the ECH81 first mixer, I think modern radios are building ever more complex sandcastles rather than pyramids. ( Mc/s and kc/s as in the EA12 manual) Ian, G4ICV, PP-ASEL, AB2GR, K2 #4962 -- _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
