A note on tuning amps for maximum out, or the legal limit on the SSB ot
CW/tune position?
There are many amps, particularly older ones with a tune and SSB
position as well as many of today's minimal amps. By minimal, I mean
those with a substantial voltage drop under load.
Those older amps were "supposedly" designed to have the same plate
impedance in either setting. With those, you often would get more power
out by tuning in the CW/tune position with little voltage sag than
tuning for max out in the SSB position.
There was the old "tune it where you are going to run it", but many
didn't realize (or know) that the amps did not have a PS robust enough
to tune a carrier to max in the SSB position without excessive voltage
sag which with the higher voltage on peaks would leave the amp
mistuned. Many of today's "legal limit" amps suffer from anemic power
supplies as well as overly optimistic ratings. These amps do not have
the gusto to operate at their rating in PS and/or tubes. Often the band
switch and coils are over rated as well, let alone with AM linear.
I'd pulse tune for max and drive it with unmodulated carrier to 1/4 of
that (IF the components can handle it), keeping in mind there is a
legal limit if your amp will go that high. Remember those old amps were
rated for and designed for a 1KW input, or 2KW PEP. About half of
today's legal limit...EXCEPT on AM
In those days, efficiency was considered more important than it is today.
73
Roger (K8RI)
On 10/30/2014 3:00 PM, Glen Zook via Amps wrote:
The problem is that "desired communications" is not defined!
If the operator desires to have a 40 dB over S-9 (with S-9 defined as a 50
microvolt signal level) at every location, then that operator can run more
power, and still obey the rules, than an operator who just desires that their
signal can barely be detected above the noise level. Glen, K9STH
Website: http://k9sth.net
On Thursday, October 30, 2014 11:00 AM, Drax Felton
<draxfelton@gmail.com> wrote:
And this one too...
At all times, transmitter power must be the minimum necessary to carry out the
desired communications.
On Oct 30, 2014, at 10:16 AM, Robert Logan via Amps <amps@contesting.com> wrote:
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
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|