Best AM demodulator?

[colly0410]

If money was no object in forum members opinions which form of AM demodulation would be best for least distortion? I'm thinking of half wave & full wave diode detectors, anode bend, grid leak, synchronous, quasi-synchronous or some other type I've not thought of...

[ppppenguin]

Presumably synchronous. All rectifierand non-linearity based detectors have significant distortion.

[Pat Pending]

Presumably synchronous. All rectifierand non-linearity based detectors have significant distortion.

Do you mean with a PLL Jeffrey?

But for something less exotic, active rectifier detectors?

Andy.

[colly0410]

Never thought about 'active rectifiers' being used as a detector, heard about them in power supplies though.... I know synchronous detectors can cope with asymmetric sidebands & carrier cancellation & over modulation; I understand how it copes with the sidebands & the carrier fluctuating in fading, but not how it copes with over modulation.... What sort of distortion is caused by diode detectors?

[ppppenguin]

Interesting article on syncrhronous detection

http://www.valveradio.net/radio/synchron...radio.html

[pwdrive]

Wonder what a Tayloe detector would be like on conventional AM?

Lawrence.

[Pat Pending]

Never thought about 'active rectifiers' being used as a detector, heard about them in power supplies though.... I know synchronous detectors can cope with asymmetric sidebands & carrier cancellation & over modulation; I understand how it copes with the sidebands & the carrier  fluctuating in fading, but not how it copes with over modulation.... What sort of distortion is caused by diode detectors?

Of course I ment "precision" rectifiers (must turn off predictive text!)

Simple diode detectors produce a nonlinearity distortion that is particularly bad when underdriven, (similar to crossover distortion in a class B amp it could be said?)

Interesting article on syncrhronous detection

http://www.valveradio.net/radio/synchron...radio.html

Maybe worthwhile for HF bands for "all mode tune through" as well as better audio.

[peter scott]

Interesting article on syncrhronous detection

http://www.valveradio.net/radio/synchron...radio.html

The AM performance with strong adjacent stations and noise sources is very impressive.
https://www.youtube.com/watch?v=R1Kft3M1oec&feature=youtu.be

Peter

[Ed_Dinning]

Hi Gents, I think there was a definitive article by Prof Tucker (Bham uni) in either EE or WW in the 50's. I believe this was later revisited by WW.
Has anyone the references?

Ed

[Synchrodyne]

See:  http://www.thevalvepage.com/radtech/synchro/synchro.htm for what is said to be a transcription of the Tucker article in the Journal of the British Institution of Radio Engineers in April 1954.

Wireless World 1948 August carried an article by “Cathode Ray” which drew from Tucker’s article in Electronic Engineering 1947 March.

However, the history of synchronous AM demodulation is much broader topic than covered by  Tucker’s Homodyne and Synchrodyne articles.  It was long a goal for both radio and TV vision demodulation, but realized in terms of mass-produced consumer-level products only in the IC age.  I unearthed some of the history, albeit in a disjointed way, in connection with the old UKVRR thread:  https://www.vintage-radio.net/forum/show...post348392, and have since found a bit more.

Be that as it may, I should answer the original question by saying some form of well-executed synchronous demodulation, whether PLL fully synchronous or quasi-synchronous, the choice between the two being circumstantial.  Even the best rectifying demodulator, perhaps the precision rectifier, will distort with sideband asymmetry and if fading causes the carrier to drop enough to cause the modulation to go beyond 100%.

The circumstantiality of the choice between PLL fully synchronous and quasi-synchronous is well illustrated by the Motorola C-QUAM AM stereo decoding ICs.  Envelope demodulation was done by a very low-distortion quasi-synchronous demodulator, this ensuring that the reference channel carried the same phase modulation (PM) as the signal, and so the PM did not distort the output.  On the other hand, the I and Q signals were recovered by PLL fully synchronous demodulators.


Cheers,

Steve