"And now for something completely different..."

bbruhns at erols.com bbruhns at erols.com
Tue Feb 16 14:35:49 CST 2010

Complexity is relative.  Ampliphase may have been more efficient than plate modulation, but I don't think that it caught on that much in the USA.  I assume that station owners didn't see enough of an advantage to offset their worries.  They didn't really understand even the simple plate modulation technology, in my opinion, or I think that they would have gone with triode audio power tubes and tetrode or pentode RF power tubes in the conventional class-AB / class C plate-modulated transmitters pretty much from the 30s.  So convincing them to go with some remarkable vector combination  system like Ampli-Phase, as cool as it really was, was a tough sell.  To me, the reduction in overmod spatter, the good efficiency, and the improvement in audio quality, would have made the sale.  No big heavy modulation transformer to blow out, either.  But they were nervous investors.

   Bob, WA3WDR

------Original Message------
From: andre kesteloot
To: Bob Bruhns
Cc: Tacos AMRAD
ReplyTo: andre.kesteloot at ieee.org
Subject: Re: "And now for something completely different..."
Sent: Feb 16, 2010 11:28 AM

Bob Bruhns wrote:
> In the old days, there were a few other alternatives to plate modulation that did get reasonably good efficiency.  One was called
> AmpliPhase, it belonged to RCA and it combined two oppositely phase-modulated output stages. [...] Ampli-Phase
> was commercially viable, and some stations used it.  The inherent linearity of the Terman-Woodyard and Taylor systems were not so
> good, but I understand that with enough negative feedback, they were OK.
> The problem with those systems was complexity, and adjustment was difficult, and multi-frequency operation was tricky. That was an
> issue with the old Conelrad requirements for stations to be able to transmit on 640 KHz or 1240 KHz, and also on shortwave where a
> transmitter might be expected to change bands a few times a day.  

I am somewhat familiar with Ampliphase transmitters. The Conelrad 
regulations did not apply overseas and medium-wave transmitters were 
easy to adjust, and the lower power consumption made it easier on 
ventilation (or A/C) requirements (not to mention the electric bill).
For short-wave operation, tuning, unfortunately, was not quite as 
simple; as the transmitting station usually has to switch from one 
frequency to an other (and one short-wave band to another) in a very 
short time.


Sent from my Verizon Wireless BlackBerry

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