clifto wrote:
generally have no significant signatures either. TRF radios lack
oscillators, hence have no significant EMI/RFI signature.


The only TRF radio I ever owned certainly had an oscillator. Matter of
fact, it had two, one in the mixer stage and one BFO.

There seem to be two different definitions of "TRF" floating around.

Definition #1:
A TRF radio has one or more tuned RF amplifier stages before the mixer.

Definition #2:
A TRF radio has no mixer. There are one or more tuned RF amplifier
stages, then a detector, then one or more audio amplifier stages.

The former would be less likely to radiate spurious local-oscillator
signals; they would have a harder time leaking through the RF amplifiers
backwards. It could however happen.

The latter is how many (most) radios were built before Armstrong
invented the superhetrodyne circuit. (before there was such a thing as
a mixer) No local oscillator exists to be radiated. On the other hand,
it's difficult to keep a set like this stable and to keep the tuned
circuits tracking on the same frequency.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com