With all this interesting discussion re ALC vs PSK-31 vs distortion, I thought
I would re-post something I posted to the list five years ago. Although my
test was using the Jupiter, I suspect that many Ten Tec rigs would yield
similar results. Here is what I posted:
>
> I almost always read that one should not operate into the ALC
> range in PSK31 [and I suppose most other sound card modes].
> On the other hand, one of the outstanding characteristics of Ten
> Tec rigs for the last few generations, has been ALC stabilized
> output at any power level within the transmitter's power range.
> I have always operated PSK just on the edge of ALC control. Is
> that good or bad? Don't know...............so I decided to run a test to
> see what effect ALC had on signal quality.
>
>For the test, my main rig was Pegasus
> connected to a dummy load with a very short piece of wire clipped to the
> "hot" lead of the D/L and the power output set at 30 watts in the TUNE
> mode. My test receiver was an Argosy with about 4" of wire connected to
> the antenna jack. I have a 20db user selectable atteuator in the Argosy
> so I had that in line. With my Pegasus keyed and sending PSK, I got a S9
> reading on the Argosy, so I clearly was not overloading it. Both radio's
> had computers attached running Digipan. The interface between the Peg and
> my computer is a home built isolator with a transformer, resistive
> attenuator and trim pot level adjust. I leave the mic setting on the Peg
> just where it is when I operate SSB. I adjust the output level slider
> on the sound card to 50% scale. Then I adjust the trim pot on the
> interface until I JUST come into the ALC range. I then make any fine
> adjustments in transmit level with the sound card level slider. OK,
> that's the setup.
>
>
> The results of the test were quite interesting. With the sound
> card adjusted so the ALC light never illuminated, I saw IMD
> readings on the receive channel of around -32 to -33db. When I
> brought the sound card level up to the point where the ALC light
> just illuminated solidly, I saw -30 to -31db! And when I opened
> the sound card level to full output, putting the Peg into deep ALC
> range, I still saw IMD levels in the -27 to -28db range! And the
> waterfall confirmed the above readings by being almost text
> book perfect at all settings of the level control.
>
>
> So the answer to the question is....not bad to run the
> Pegasus/Jupiter lightly into ALC range on PSK. The transmitted
> signal will be one you can be very proud of and you will enjoy
> stable output power as the rig heats up during transmit cycles
> and the level adjustment will not be critical.>
>
73,
-Lee-
WA3FIY
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