Re: [Repeater-Builder] Re: Audio Reproduction

[scomind]

Hi Coy,   First I would like to read each of your personal definitions of FM and PM, then your dissertations on exactly why one is better than the other, Complete.     FM and PM are both referred to as "angle modulation" because the the radio wave's "angular velocity" (frequency or phase) is being modulated rather than its amplitude (as in AM).   (If the term "angular velocity" isn't familiar to some, you've seen it pictured. It looks like a clock face with a single hand on it. If you rotate the hand in little steps and put a dot where the pointed end of the hand is at each step, you'll draw a dotted circle. If you plot a graph of those dots on a horizontal axis, you'll get the familiar sine wave. That means that a sine wave can be described either by its frequency or by how fast the clock hand rotates - - its angular velocity.)   Anyway, an FM signal deviates according to the amplitude of the modulating waveform, and a PM signal deviates according to the amplitude and the frequency of the modulating waveform.   Since the only difference between the two is the frequency aspect, you can easily convert one to the other and back again. If you take a PM signal and integrate it (deemphasis), you get FM. If you take an FM signal and differentiate it (preemphasis), you get PM. The math appears in any number of communications handbooks. We do it all the time in our rigs.   So, THEORETICALLY, there is absolutely no difference between PM and FM when it comes to the hot-button issues of distortion, frequency response, and other "quality of sound" issues.   In PRACTICE, there are lots of issues. We've been kicking them around on this list for years. For example, accomplishing PM with varicaps means it's hard to get a lot of deviation at low CTCSS frequencies. It's not because there's anything wrong with PM, and in fact, a nice Agilent function generator will do this very well! But the exciters that we have available to the hobby today at cheap prices do have drawbacks.   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.