Re: [Repeater-Builder] Re: Audio Reproduction

[scomind]

Hi Joe,   Bob (S-Com Bob), would it be a fair statement to say that traditionally, transmitters have generally been PM (either true PM or emphasized FM), but receivers have been FM all along? I base this on your last post.   Yes, absolutely!   To further state the case, assume that there are two parallel universes.   In one universe, all hams use phase modulators and phase demodulators. The terms 'preemphasis' and 'deemphasis' are unheard of. The whole system has flat response. Since their phase demodulators track their phase modulators, the hams communicate via voice and data over their PM systems, all the way down to DC. They don't transmit "preemphasized audio" because they don't even know what that is. They've never seen it. You put flat audio in and you get flat audio out, including DC.   In the other universe, all hams use frequency modulators and frequency demodulators. The terms 'preemphasis' and 'deemphasis' are unheard of. The whole system has flat response. The hams communicate via voice and data, all the way down to DC.   One day, a rip occurs in the space/time fabric and an FM-equipped ham hears a PM transmission from the other universe. It sounds tinny. Why? Because the FM guy's frequency demodulator (discriminator) is a differentiator. It pre-emphasizes the PM transmissions, so he hears attenuated lows and emphasized highs.   So, which end is responsible for the tilt?   Is the FM ham correct in saying that the PM guy is transmitting a 'nonstandard' signal with preemphasis? In an FM universe, PM seems strange because it has a tilt to its response.   But the PM ham has never even heard of preemphasis, and has certainly never had to use it. He assumes the FM ham's receiver is responsible for the the tilting. After all, a frequency demodulator isn't sensitive to the phase of the incoming signal, it's sensitive to the rate of change of the phase, so the FM ham must be using a wierd receiver.   We live in both universes. We've decided that we will always transmit PM - - it doesn't matter whether it comes from a PM transmitter or an FM transmitter with preemphasis, it's PM mathematically. And, we've decided that we will always receive with a frequency demodulator.   Because we are crossing the two systems, we will always have to deal with the existance of preemphasis and deemphasis.   It's neither good nor bad, it just is.   But when you look at the picture as described above, it sort of nullifies what all of us have been saying for a long time - - that preemphasis is a natural result of phase modulation. No, preemphasis results from demodulating PM with a frequency demodulator. It seems like preemphasis ought to be a natural result of PM, but that's because we only think in terms of discriminators. After all, all of our receivers and service monitors have them and no one has a phase detector. But it might be good to keep the big picture in mind during some of these theoretical discussions.   73, Bob Yahoo! Groups Links To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/   To unsubscribe from this group, send an email to: [EMAIL PROTECTED]   Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.