[TenTec] OmniV and PSK31 -- any experience to be shared??

[Rick Denney]

Paul writes...

> Sounds like the problem here is when someone reads, "Open the TX 
> full" they think that means TX at full output. When I started in PSK
> I ran at a lower power level (15W on an ArgoV) but as I've been away
> for about a year I posed the question to the digital newsgroups. The
> majority said the current trend is to run the TX "full" but reduce 
> the power out by sound input - something about more linearity.

Let me try and explain this in audio terms to make sure I have it
right. I will be experimenting with PSK31 soon.

When setting up an audio public address system, there will be at least
two components that handle amplification. One is the mixer board, and
the other is the PA amplifier. Audio power amplifiers have one or two
controls: They have an on-off switch, and some (only some) have a
master level control for each channel. Audio engineers routinely set
those to full, or zero attenuation of the signal coming into the
amplifier. Then, they reduce the amplification using the mixer board,
which attenuates the audio signal going into the amplifier.

The reason is they want the peaks of the audio signal to be farthest
from the peak output of the amplifier as possible. They call that
"headroom", and more headroom reduces the risk of pushing the power
amplifer into overdrive, where it becomes non-linear (at best) or
where it clips (at worst).

So, my understanding from reading this is that we want as much
headroom as possible between the audio input signal and the audio/RF
amplification of the radio. Thus, we set RF output to max, and then
attenuate audio input to a low value. That provides the maximum
possible headroom to achieve the desired 30 or 35 watts of output. If
the radio was 15 watts max RF output, we would set it to max, and then
attenuate the incoming audio to an output of 5 or 6 watts to achieve
the same result, it seems to me.

In the end, it seems to be about headroom. Run the final amp and full
amplification capability, but attenuate the input signal to keep it in
the loafing range.

With phone, we tolerate more distortion in the signal to get a little
higher average loudness. That's why we have speech processing, etc.
Broadcast stations do that, too, and even when fidelity standards are
really high, they still worry about how loud the signal seems. But
with digital, we don't need or want any of that distortion.

Did I get that right?

Rick, KR9D