On Sat, 13 Jan 2007 17:43:52 -0500, "Jimmie D"
wrote:

+++
+++"Jimmie D" wrote in message
. ..
+++
+++ "Telstar Electronics" wrote in message
+++ ups.com...
+++ Jimmie D wrote:
+++One thing did get me thinking. I
+++ have a nice scope to look at the output of my TX and to lookat the
+++ output of
+++ the processor , for me its a piece of cake to setup. How can you do this
+++ without test equipment?
+++
+++ Absolutely, I have a nice Tektronix scope I use...
+++
+++ Don't miss seeing the new CB Radio Speech Processor Prototype at
+++ http://www.telstar-electronics.com/d...s/WhatsNew.htm
+++
+++ But how does most of the people who buy them do it?
+++
+++Even a good quality limiter/compressor is just anotheer splatter box if its
+++not set up right.
+++
************

The theory behind a compressor amp is to provide a more constant power
signal to the modulator. There have been many schemes in the past 70
yrs or so to do that. Even to the point of what was once called Super
Modulation.

A properly setup with compression will not have excessive compression
and also not use the compression stage as the major gain stage. Where
most compression schemes come into dislike is when the person using it
feels he needs to get far more gain from the circuit than is really
necessary and so much compression that you can hear a roach fart 20
feet away.

The idea behind audio compression and other audio/rf processing
schemes is to increase signal to noise ratios. When using AM and the
carrier is already 30 dB above the ambient atmospheric noise then any
processing is typically useless. The gain in signal to noise ratio is
not worth the effort or even the cost of adding such a circuit. Audio
compression is totally useless on FM unless you want a constant
deviated signal. For what ever reason that one would want this is
beyond all logic.

Even when the AM signal is marginal to the atmospheric noise, audio
compression alone yields between 1 and 2 dB improvement in the
received signal to noise ratio. On AM, when you are at 6 to 8 dB
signal to noise ratio, improving one to two dB is generally worthless
improvement.

james