I think I should mention that 375W is for a 100% modulated sine wave. Since
speech is asymmetric and various compression/clipping methods allow much
higher positive peaks while clipping the negative ones at around 95% a
higher resulting in more "talk power" for 1500W PEP.
I dont know of anyone that is that fussy to worry about it anyway on AM.....
or SSB or CW where the amps are tuned for max anyway no matter what the
power is.
With rigs that permit a single sideband AM the equation changes.
Carl
KM1H
----- Original Message -----
From: "Robert Logan via Amps" <amps@contesting.com>
To: "Kimberly Elmore" <cw_de_n5op@sbcglobal.net>
Cc: <Amps@contesting.com>
Sent: Thursday, October 30, 2014 10:16 AM
Subject: Re: [Amps] AL1200 on AM - max carrier?
Thought I might mention the legal limit for AM is 375 watts carrier. Bob.
NZ5A
Sent from my iPhone
On Oct 30, 2014, at 9:04 AM, Kimberly Elmore <cw_de_n5op@sbcglobal.net>
wrote:
Any amp will be inefficient when used as a linear amplifier for AM because
as drive is reduced, efficiency is reduced. They will all generate a lot
of heat in this application. However, the AL-1200 should hold up well to
the lock-and-talk culture. In AM, PEP is 4X the carrier, Overall, you want
the carrier to be at 1/4 of the amp's rated PEP output.
Assuming the driver generates 100 W output, tune the amp for max or 1500
W output (whichever comes first) with the amp in SSB mode. You want SSB
mode because you want the best linearity. Whether or not you use SSB or CW
makes little difference in the efficiency for your application but makes a
big difference in linearity.
Usually, when the driving rig is in AM mode, the carrier is reduced to 1/4
of the max PEP SSB output. In such cases, you should see no more than 375
W carrier power (375 x 4 = 1500).
If you are trying to drive it with an older plate-modulated tube rig, you
ill have to be careful if you reduce the power output because the
modulation transformer is designed with a particular output impedance in
mind. If you reduce the drive to the PA, the impedance changes and you
will have to set the proper audio level using a scope or modulation
monitor.Start with audio gain at zero, bringing it up slowly. Otherwise,
you risk arcing in and destruction of the modulation transformer.
Kim N5OP
On Thursday, October 30, 2014 8:05 AM, Gary Smith <Gary@ka1j.com> wrote:
One thing for sure, run it at the CW
setting, use the lower KV setting and you
will run far cooler for a given KW out.
73,
Gary
KA1J
I want to run my AL-1200 on AM for a short stint (2 hours operating
time, 50% overall duty cycle). I have tested it at about 225 watts
carrier output, and with moderately high duty cycle transmissions (known
in the AM crowd as 'Old Buzzarding'), it gets quite hot.
What is the max recommended AM carrier power for long-winded
transmissions?
Also, I'm assuming it should be tuned up for proper operation at double
the carrier power.
I searched the list finding no real answers.
Thanks,
Tony, K1KP
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