Howdy, You make my point. You say "Our system" You are a controller guy. Your controller is your perspective. But that is actually a device perspective.
Sure, I'm a controller guy, and since S-COM is going headlong into the multiport controller biz, I have a vested interest in this topic. For instance, how does a customer tie a bunch of radios, some running flat and some running pre-emphasized, into one big controller? It only works for receivers and transmitters that have similar audio schemes. It won't work if, say, RX1 (flat output) is supposed to mix with RX2 (discriminator output) and the resulting audio feed both TX1 (flat input) and TX3 (modulator input). The solution seems to be to run flat audio within the controller, but that may not square with everyone. Also, with regard to this statement: "... can't change the flatness. Pre-emphasis is always precisely +6.000 dB/octave and de-emphasis is always precisely -6.000 dB/octave. " Real world transmitters always have limiters. Those DO change flatness. Just look at the EIA/TIA specication for testing transmitter pre-emphasis. The test is not run at system deviation. It is not even run at 60% of system deviation. It is run at 20% of system deviation. [that's +/- 1 KHz deviation for 5 KHz systems] Run the test at 20% into a modulation analyzer and you get a nice 6 dB per octave line from 300 to near 3000 Hz. Run it again at higher deviations and see what the limiter does to your nice straight line - the pre-emphasis curve hits the limiter at progressiviely lower and lower frequencies as you increase the deviation. While those tests are valuable, we don't communicate with sweep generators, we communicate with the human voice. And the human voice has a natural -6 dB/octave rolloff, which means that ultimately all the audio gets clipped pretty much the same. (Please see W0INK's paper at _www.scomcontrollers.com/downloads/pmmodandnbfm.pdf_ (http://www.scomcontrollers.com/downloads/pmmodandnbfm.pdf) ; the same paper was published in the Winter 2007 issue of CQ-VHF magazine, which came out about a month ago. There's a discussion of this topic starting at page 3.) 73, Bob, WA9FBO <BR><BR><BR>**************************************<BR> AOL now offers free email to everyone. Find out more about what's free from AOL at http://www.aol.com.
