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Michael Black[_2_]

On Wed, 15 Jun 2016, wrote:

"** So they are cheap and nasty piles of Chinese junk that sell for
like $40 ? "

No, they go for quite a bit more than that, but I bet you are probably
close to the actual cost of them. And damnear everything is Chinese
junk. Any company publicly traded in the US is pretty much governed by
Dodge v Ford.

"No way are they TRF cos that is impossible. "

Why ? I tellya I seen the cores lower in the adjustable
coil/transformers lower in the channels with the lower frequency. Are
you saying that is all front end and they still downconvert ?

How wide is the deviation?

I finally took apart some RCA Carphones last fall, 2M tube receivers with
a bunch of coils in the front end. Yet it's still wider than the
deviation on that thing, and of course they had to downconvert for enough
selectivity.

There's a good reason TRF receivers are long in the past. You don't get
enough selectivity (and these things are operating much much higher than
the Am broadcast band), you have to retune all the tuned circuits if the
frequency is changed, and gain has to be at the signal frequency. This
latter means that you might have trouble getting enough gain, and making
it stable may be an issue. I thought you said these could be changed to
another frequency, the last thing you want is an end user having to retune
the front end.

Some things still use superregenerative receivers, that provide lots of
gain but the quenching makes it stable. But those are as wide as the barn
door, and FM is detected by slope detection, ie enough selectivity so
there's a frequency to amplitude conversion, and then the signal is
received as AM. Lots of noise if you lose the transmitter, you also don't
get the limiters (and advantages of those limiters) that you see in a
proper FM receiver.

And as pointed out, there are crystals in there, so it must be a superhet.

Michael