On 1/15/2011 10:47 PM, David Nebenzahl wrote:
Trying to teach myself electronics, I've been reading a few textbooks I
inherited on the subject. Tough going, as my math is in serious need of
repair.

Anyhow, found a couple of interesting things in these older books:

1. TRF:

In the section on modulation, demodulation and other radio-related stuff
one book brings up "the tuned radio-frequency receiver" before
discussing superhet, as one would expect. But they say;

During the evolution of radio, the tuned-radio-frequency (TRF)
receiver was used to receive AM signals. Today, a few special
applications still use TRF receivers.

Now, they go on to explain why TRF is inferior to superheterodyne. But
I'm curious: are there still any radios that use TRF? and why? (Keep in
mind this book was written in 1979).

The Realistic TRF (12-655) radio was sold into the (IIRC) mid-80s:
http://www.radiomuseum.org/r/radio_s...range_trf.html
This link indicates that it was actually a superhet with an RF stage; I
was under the impression all these years that it was a solid state
analog to an AK-40 or similar. Oh well.

TM