[TenTec] speech processing idea

[Dr. Gerald N. Johnson]

On Fri, 2006-10-27 at 00:30 -0400, Gary Hoffman wrote:
> They had pc's in 1958 ?  Interesting.  I was still using mainframes and
> terminals in 72....shows how much I missed.
> 
> 
Not really PCs. Tended to take up a whole room or building, and tended
to have lots of noise from the card readers. I don't know of any
analogue inputs in real time.

But speech clippers were tried and they caused much splatter on SSB.
Even when filtered. The only effective clipping was RF clipping that was
reformed by running the clipped IF signal through another mechanical or
crystal filter. But fast acting ALC sometimes does as much. Though one
rig's popular mod was to add 10 MFD to the ALC line for more punch. But
then the PA was driven to clipping for a long time before the ALC could
do anything. A case of slow AGC.

The tests on punch power that I've done hint that the relative phase
responses of the microphone, audio stages, and SSB filter have a great
effect on the average power. I've only gone through trying several
microphones. I have a Turner made for shipboard steam boiler room
service that weighs a ton (and its a hand microphone) that in one of my
VHF rigs gives great punch. It may be that its a bit bassy and so keeps
down the higher frequency parts of my voice to cut back on the peaks
that can be inherent when mixing multiple tons of similar amplitudes.
The peak to average power of a multiple channel cell phone amplifier
goes down with each additional signal. RF clipping only raises the
intermod and interference between those signals so the PA has to get
along with the condition. That could well be a fundamental problem in
SSB that average power is always going to be significantly lower than
peak power and there is no solution that doesn't introduce excessive
intermod which is usually detected as splatter.
-- 
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer