RadioBanter - View Single Post - Need Info on Hallicrafters SX-28/SX-28A Modification

Chuck Harris · November 18th 07, 05:22 PM posted to rec.radio.amateur.boatanchors

wrote:
On Nov 18, 7:44 am, "COLIN LAMB" wrote:
Although I am not familiar with an additional if stage, it seems there would
not be much advantage in adding such a stage. Any additional gain would be
at a cost of reduced dynamic range.

I would be more inclined to think it was a product detector circuit, using a
6BE6.

Colin K7FM

A product detector was also my first thought, but why the IF can?

Because a product detector works at IF/BFO frequencies and puts out
audio. Most of the high performance product detectors of that time
frame used a scheme that required at least one center tapped transformer
that works at IF frequencies. Look up some circuits for diode ring
demodulators.

Plus, the passive balanced demodulators are usually a bit lossy, so
there might be a need to pump up the IF gain a bit to compensate for
the demodulator loss.

-Chuck