Single ECH35 Synchronous AM Detector

[Alejandro Lieber]

The original 1947 (no diode) Synchrodyne AM detector by D. G. Tucker,
using a single ECH35:


http://lieber.com.ar/Synchrodyne_Detector.jpg



--
Alejandro Lieber LU1FCR
Rosario Argentina

Real-Time F2-Layer Critical Frequency Map foF2:
http://1fcr.com.ar

[Alex Pogossov]

Curious circuit. Thanks.

But as many others it is a pull-in locked oscillator, which means if the
modulation is deep, it will be losing lock at the troughs of the envelope,
distorting the signal.

Nevertheless, the author made an attempt to lock the synchronous oscillator
in phase with the carrier, not at 60 degrees as usually happens. Those who
experimented with low end "communication receivers" with so called product
SSB detector (such as Trio 9R-59DS or Lafayette HE-80, HA-225, etc) probably
noticed that on strong AM stations the product detector does lock, but it
locks naturally at 90 degrees. The sound becomes tinny, the detector picking
up secondary phase modulation (caused by sideband asymmetry) rather than
true AM.

Quadrature lock happens because of capacitive coupling between the signal
and BFO, in this case through space charge.

In the presented circuit Mr. Tucker introduced another 90 deg phase shift.
He did not decouple g2,4 of the hexode to GND. As a result, signal on g2,4
is 90 degrees lagging due to the inevitable capacitance from g2,4 to GND. In
turn, g2,4 are capacitively coupled to the oscillator via capacitance
between g2,4 and g3 sandwiched between the former grids. So we have two 90
degrees shift which eventually provides lock in phase with the carrier.

Regards,
Alex(andre)

"Alejandro Lieber" > wrote in
message ...
> The original 1947 (no diode) Synchrodyne AM detector by D. G. Tucker,
> using a single ECH35:
>
>
> http://lieber.com.ar/Synchrodyne_Detector.jpg
>
>
>
> --
> Alejandro Lieber LU1FCR
> Rosario Argentina
>
> Real-Time F2-Layer Critical Frequency Map foF2:
> http://1fcr.com.ar

[Patrick Turner]

On Sep 21, 6:31*pm, "Alex Pogossov" > wrote:
> Curious circuit. Thanks.
>
> But as many others it is a pull-in locked oscillator, which means if the
> modulation is deep, it will be losing lock at the troughs of the envelope,
> distorting the signal.
>
> Nevertheless, the author made an attempt to lock the synchronous oscillator
> in phase with the carrier, not at 60 degrees as usually happens. Those who
> experimented with low end "communication receivers" with so called product
> SSB detector (such as Trio 9R-59DS or Lafayette HE-80, HA-225, etc) probably
> noticed that on strong AM stations the product detector does lock, but it
> locks naturally at 90 degrees. The sound becomes tinny, the detector picking
> up secondary phase modulation (caused by sideband asymmetry) rather than
> true AM.
>
> Quadrature lock happens because of capacitive coupling between the signal
> and BFO, in this case through space charge.
>
> In the presented circuit Mr. Tucker introduced another 90 deg phase shift..
> He did not decouple g2,4 of the hexode to GND. As a result, signal on g2,4
> is 90 degrees lagging due to the inevitable capacitance from g2,4 to GND. In
> turn, g2,4 are capacitively coupled to the oscillator via capacitance
> between g2,4 and g3 sandwiched between the former grids. So we have two 90
> degrees shift which eventually provides lock in phase with the carrier.
>
> Regards,
> Alex(andre)

Well, that kind of Synchrodyne for BC band didn't seem very popular.
With those pots, maybe different and critical settings would be needed
for different carrier F, and thus keep ordinary ppl swearing at their
radios.

Patrick Turner.