I'll show my age by doing this, but lets revert mentally back to the
Collins S Line. The transceiver, using a pair of 6146's in the PA, was
most efficient and linear when properly tuned and loaded. It produced
about 120 to 140 watts of PEP output. And there was NO Power control or
method to reduce the power as we know it today. Introduce the 30L1
linear amplifier, being 4 x 811's, which required about 60 to 80 watts
of drive to reach maximum rated output. So the issue now is, how do we
get the properly tuned and loaded transceiver down to the correct drive
level for the 30L1? ALC is the Collins answer. Thus the voltage
determined by the amplifier grid current was fed back to the inter-stage
of the driving transmitter to effectively reduce the output while still
retaining the correct tuning and loading of the transceiver PA.
Today it seems that the designers have monkeyed around with the time
constants in the ALC algorithm to improve certain aspects of the signal,
thus reducing key clicks and overshoot, but seemingly at the sacrifice
of certain other areas of the signal. Thus we find that ALC is not to
be used to control power or raise the average power but designed to
prevent over drive of any stage. Correctly, Speech Processing is deemed
much more effectively used and with less undesired effects on speech
than ALC. In fact, one amp manufacturer says "run the transmitter at
full power and let the Smart ALC in the amplifier adjust the required
drive accordingly via the ALC signal". Oh wow! Certainly asking for
trouble in my thinking.
In my world of audio, ALC is much like limiting with an input to output
ratio of 20:1. This says a 20 dB increase on the input causes only a 1
dB change in output. Now enter compression, where the input to output
ratio is anywhere from 1:3 to about 10:3. Again a 10 dB input change
yields a 3 dB output. Of course there are different attack times and
release times applied to both limiting and compression. Newer
technology systems have the ability to analyze the various components of
the input signal and adjust the attack and release times quite
effectively. Many Speech Processing algorithms have the same ability.
Thus they are better suited for raising average PEP output.
A second factor existing is the issue where hams like to see their power
meter indicate the rated transceiver power. With some of the electronic
power measuring devices that may work OK. However, with mechanical power
indicating devices, the ballistics of the meter movement, meaning the
slow response and overshoot damping, will not allow a mechanical meter
to correctly show the energy level of ones SSB voice signal. The
typical mechanical movement shows about -6 dB less or 25 watts for a 100
watt PEP signal. Of course speech processing will raise the average PEP
level, but again the true PEP remains at 100 watts.
And as Paul Harvey would say; "and now you know the rest of the story".
73
Bob, K4TAX
On 1/31/2022 9:01 PM, elecraft-requ...@mailman.qth.net wrote:
On Jan 30, 2022, at 1:10 PM, Fred Jensen<k6dg...@gmail.com> wrote:
I can remember, shortly after SSB appeared on the ham bands that "ALC" showed
up and was immediately inducted into that top category of things like canned beer and
sliced bread. It would reduce the dynamic range of your signal and fill out your RF
envelope with DX inducing energy. It didn't matter if you preferred the James Earl Jones
sound by close talking your microphone, or the Storm Drain sound with the gain up and
speaking from across the room. Not to worry, ALC will take care of it for you and you
will fully pack your RF envelope.
Tomorrow is the first day of February 2022 and ALC occupies a less than coveted spot in the same
category that also contains last night's broccoli casserole. One wonders why manufacturers even
put connectors and meters labeled "ALC" on their radios. "Four solid bars, and the
fifth barely flashing because the fifth bar is where ALC starts. Just barely flashing ... you DO
NOT want to engage the ALC!"
I realize that while we believe that the rules of electricity don't change and
none of us ever inspect our electricity very closely ... if we did we'd find
the power company is selling us used electricity as if it was new ... what
changed? If ALC was slicker than snot back then, why isn't it now?
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to arch...@mail-archive.com
