[Elecraft] 8 pole vs 5 pole..I knew this would happen

[Ian Stirling]

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
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