--- In Repeater-Builder@yahoogroups.com, [EMAIL PROTECTED] wrote: "... Our system takes flat audio in and delivers flat audio out..."
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. Your device wants "flat" audio in and out. Flat in the sense that it is neither pre-emphasiszed or de-emphasized as it arrives at your device and as it leaves your device. Flat in the sense that you won't alter the frequency response of that audio on its way through your device. The receiver that precedes your controller is another device. From its perspective, de-emphasized audio is not flat. It can't be by definition. If you are connected to de-emphasized audio, the receiver IS changing the frequency response. If you are connected to discriminator audio, it is "flat", i.e. not changing the frequency response. Keeping a clear perspective on the differences between devices and systems IS the issue. At any given point in a system, audio may be flat or it may not be - with respect to some other point. For a clear understanding of the system, we should also clearly understand the action of each device. 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. The result of this fact is going to alter the audio characteristic going through your repeater. It's one reason why level setting is so important. It is also a significant reason why it's difficult to get a repeater to sound like simplex. Another post suggested checking the frequency response of your repeater. Definitely - do that. Try it a various deviations. You may be surprised at how ugly it gets.
