[Boatanchors] [ARC5] Taylor Super Modulation andRothmanModulation

[Carl]

----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: "mac" <w7qho at aol.com>; "Henry Mei'l's" <meils at get2net.dk>
Cc: <boatanchors at mailman.qth.net>
Sent: Thursday, February 03, 2011 3:26 AM
Subject: Re: [Boatanchors] [ARC5] Taylor Super Modulation 
andRothmanModulation


>
> ----- Original Message ----- 
> From: "mac" <w7qho at aol.com>
> To: "Henry Mei'l's" <meils at get2net.dk>
> Cc: <boatanchors at mailman.qth.net>; <arc5 at mailman.qth.net>;
> <milsurplus at mailman.qth.net>
> Sent: Wednesday, February 02, 2011 7:59 PM
> Subject: Re: [Boatanchors] [ARC5] Taylor Super Modulation
> and RothmanModulation
>
>
>> Rothman modulation is/was one of several carrier control,
>> screen grid
>> modulation schemes.  Some wild claims made for it as I
>> remember but,
>> in actual fact, nothing particularly remarkable about it.
>>
>> Taylor "Supermodulation" was a scheme for using a pair of
>> grid
>> modulated tubes coupled together in a novel way so as to
>> achieve
>> results equivalent to high level plate modulation but
>> without the high
>> powered audio components.  Besides the obvious savings in
>> component
>> costs and power efficiencies Taylor also made such (wild)
>> claims as a
>> greater ratio of sideband to carrier power and reduced
>> bandwidths
>> comparable to those achieved by SSB systems.  For the
>> definitive
>> analysis and critique of the Taylor system and it's
>> claimed benefits
>> see QST, December 1950, page 33 "Supermodulation" - An
>> Evaluation and
>> Explanation by Oswald G. Villard, Jr.  W6QYT.  Villard,
>> BTW, was a
>> professor in the Stanford University Electrical
>> Engineering Department.
>>
>> Other articles:
>> Radio News, Sept. 1948, June 1949, Feb. 1950, May 1950 &
>> July 1950.
>> Also,  U. S.  Patent #2,282, 347
>> Other stuff in CQ and Electric Radio as well.
>>
>> Dennis D. W7QHO
>> Glendale, CA
>>
>    Thank you so much for the citation. I was able to
> download the article from the ARRL web site, I also
> downloaded Taylor's patent from Google Patents. It will take
> some reading but I think I have an elementary understanding
> of it.
>     There have been many schemes to increase the efficiency
> of AM transmitters employing low-level modulation, the
> Dougherty amplifier is perhaps the best known one. There
> have also been numerous schemes to increase average
> modulation level; the simplest is peak clipping but that
> results in gross distortion if much is used. Other schemes
> have involved phase flippers to take advantage of the
> unsymmetrical characteristic of the human voice. These date
> back to simply connecting the microphone so that positive
> pressure on the diaphragm results in upward modulation. CBS
> Labs used a flipper in the Audimax (or was it the Volumax?),
> a pair of awful-sounding processors, CBS was good at self
> dilusion. All really result in upward overmodulation, a sort
> of mild carrier reduced DSB. As the QST article points out
> all these schemes result in increased distortion.
>    Most modern broadcast transmitters use either a
> modification of the Dougherty system (Continental
> Electronics) or pulse-modulation. The latter is capable of
> very high plate efficiency with low envelope distortion.
> Weldon's version of the Dougherty amp has substantially
> lower distortion and much better stability but still
> requires two phase shift networks. Both of these schemes
> have the advantage over plate modulation of eliminating the
> modulation transformer, an expensive device and difficult to
> make if the fidelity is to be good. Both also are capable of
> continuous full modulation, assuming the power supply is
> adequate. The latter is valuable for modern broadcast use
> where extreme amounts of processing are used.
>     BTW, is there anyone else here who remembers when AM
> broadcasting stations actually emitted high fidelity audio?
>
>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com



Yes, Dougherty works well but is pretty much a single frequency method since 
RF phasing is involved, on 75M a bit of QSY is possible but with the recent 
phone expansion AM is showing up everywhere on 80 and 40.

PDM is also a good method.

One of the problems with running trick circuits such as well over 100% 
positive peaks is that many receiver AM detectors can barely handle 90% 
before distorting. While synchronous detection overcomes that problem the 
good ones are expensive and the others loose lock easy. There may be some 
new developments coming on an inexpensive detector that a few will be 
evaluating.

With one of the amps I can run up to 125% positive peaks but only with 
certain stations on the receiving end and then others complain that "I am 
distorted" so its basically a waste of time the way things exist now.

Others are running SS Class E or SDR rigs and sound great once all setup. 
Sometimes I run the TS-950SD thru the 6KHz AM filter and into the LK-500; it 
gets outstanding reports but requires a monitor scope to keep it clean. 
Carrier power is around 300W for 600W PEP.

Another old timey method is plate modulated single ended Class A bias shift. 
Initially mentioned in one of the mid 30's monthly mags as a way around the 
expense of a modulation transformer and the poor efficiency of Heising. It 
appeared in Radio maybe, and was picked up again by CQ in the late 40's or 
early 50's. I have those issues but not easy access right now. Essentially 
it is a voice activated bias shift to reduce power consumption. When talking 
the bias is Class A, and it is Class B with no audio. Only a choke is 
required to pass the audio and is sometimes referred to as Modified Heising; 
indications are that it works well to about 90% modulation.

I dont know how hi fi it was but my parents listened to that classical stuff 
on a late 30's RCA console radio with PP 6F6's in the early 50's before 
getting an FM radio.

Carl
KM1H