----- Original Message -----
From: "Don Cunningham" <d...@martineer.net>
To: "John Hudson" <john.hud...@calema.ca.gov>;
<w8...@aol.com>; <drakelist@zerobeat.net>
Sent: Thursday, January 05, 2012 10:24 AM
Subject: Re: [Drakelist] FS: R-4B and a T-4XB
John,
"Normal" AM carrier can only be had with a true, plate
modulated rig. The Drakes don't have enough iron or a heavy
enough modulator to do much more than controlled carrier.
I've seen "mods", but......... I sure wouldn't do it to my
Drakes.
73,
Don, WB5HAK
There is another reason for using controlled carrier;
the resultant signal can be amplified by a linear amplifier
designed for SSB wtihout exceeding its limits. This is true
for both the linear in the rig and any external linear that
may be used.
I disagree only that "true" AM can be had with other
than plate modulated transmitters; there have been many
low-level modulated AM transmitters using linear amplifiers.
However, a linear will have quite low average efficiency
when used for AM. The estimate for old broadcast
transmitters using linear amplifiers was an "all day"
efficiency of around 33%. A reasonable plate modulated
transmitter has at least twice this. Modern AM transmitters
can exceed the old "limit" for efficiency by various
methods, mostly by running the RF stage as nearly a pulse
amplifier.
Controlled carrier AM works fine for communication use
but can be difficult to listen to on a receiver with a fast
release AVC. Also, measuring modulation percentage is not as
straight forward as for a conventional transmitter.
If one wants real AM its better to get or build a
dedicated transmitter but Drake makes it possible to
communicate with those who may not have SSB receivers (who
would that be?).
--
Richard Knoppow
Los Angeles
WB6KBL
dickb...@ix.netcom.com
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