[ARC5] A discussion on AGC.

[Kenneth G. Gordon]

On 9 May 2017 at 20:55, Dennis Monticelli wrote:

> Turns out that in order to achieve the simple addition or subtraction of frequency it requires a 
> non-linearity in the device.

Of course.

> A product detector has no problem demodulating AM.  It behaves somewhat like a synchronous 
> detector in that the BFO is tuned to the carrier freq.  Works well if drift is not a big problem.

I understand that method, the so-called "exalted carrier" method, but what I meant was that in 
the case of the simple single-triode product detector used, possibly invented, by Collins 
("borrowed" by Heathkit) those demodulate AM just fine with the BFO turned OFF!

I have suspected for a long time that when the BFO is turned off, those detectors actually 
work like the "infinite impedance" detector, but I have never investigated this beyond my 
suspicion.

In my earlier investigations on product detectors, I also discovered a version of a single-triode 
product detector, different from the Collins one, invented by a German, which was specifically 
designed to correctly demodulate AM with the BFO off.

Ken W7EKB

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