> "So you NEVER get excited and shout when chasing DX, so never drive the
PA to clipping??? If that never happens you are one cool ham."
Generally, when I make a mistake, it's during the initial tune-up procedure
and not during an operating event. Once I have maximized drive level into
the amp and accordingly adjusted a tube-based amp for maximum linearity,
shouting into the mic during a moment of excitement is a technical
"non-event." But, it depends on the quality of the exciter driving the amp.
If the exciter is prone to leading-edge power spikes and ALC thermal drift,
then all bets are off -- even if an ALC line is connected between the amp
and exciter.
>> A better means of proper amp operations includes the use of a scope in
>> trapezoid X-Y mode between the input and output of the amp.
> But it may not always inspire you to keep from a bit of peak
compression, will it? A little bit of peak compression can show up as a
lot of higher order intermod, otherwise known as splatter.
I have never used RF compression techniques on SSB. The transmitted
bandwidth is generally narrow enough that I see little added value until TX
bandwidth increases. Incidentally, there's been a lot of discussion
concerning inadequate "talk power" from some new radios on the Yaesu and
Icom user groups. Part of these complaints stem from the fact that as lower
and upper frequency Tx bandwidth opens up, power is distributed into these
spectrum areas. As such, lower TX duty-cycle should be expected in the
traditional narrow SSB range of 300Hz-2.4 kHz when the transmitter is
producing energy significantly above and below these values. My suspicion
is that if these complaining ops narrow their Tx bandwidth that they would
see their so-called "talk power" increase.
>> Until the advent of DSP, an even better method consisted of applying mic
>> audio to one set of scope plates while applying final RF to the opposite
>> set. The benefit is that the entire system from mic to amp antenna port
is
>> used to measure total system linearity. However, since transmit DSP
>> introduces latency, even if slight, I've found that method no longer
gives
>> an accurate display of linearity.
> It didn't work too good in the analog AM transmitter either because of
frequency
sensitive phase shifts through the audio chain. And for SSB the fundamental
is
that the envelope of the SSB signal is not the same as the envelope of the
audio
from the microphone so it won't work at all for SSB.
Not in my experience. There's generally not enough phase shift in
traditional analog circuits to significantly affect the trapezoid display
for this purpose.
Paul, W9AC
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