Re: [Repeater-Builder] Audio Reproduction

[scomind]

In a message dated 4/6/2004 4:40:39 PM Mountain Daylight Time, [EMAIL PROTECTED] writes: Why not call it what it is FM and PM ?   Yup, I agree!     While the results of FM or PM   can be received as FM if voice is used there are a few things that FM will do beter..  PM just does not work very well with very low frequencies for one thing.   This has been discussed on the list before, and what we found was this: If your PM is set up to deviate at, say, +/- 5kHz at 1000 Hz with 1% distortion, then it will deviate +/- 500 Hz at 100 Hz with the same 1% distortion. It's linear. Call it a 'constant distortion' line.   The problem occurs when you add a CTCSS encoder and try to deviate more than +/- 500 Hz at 100 Hz, or more than +/- 335 Hz at 67 Hz, and so on. The distortion increases past 1%. But that's because you are feeding the modulator with a separate tone that can be adjusted higher than the constant distortion line. Voice, even at low frequencies, doesn't have this problem. You'll get exactly the amount of deviation for any frequency as dictated by the 6 dB/octave preemphasis curve.   Admittedly, most folks want at least +/- 500 Hz of deviation at 100 Hz, and that makes CTCSS tones below 100 Hz somewhat unusable. Maybe that's one of the reasons the low CTCSS tones weren't used much (along with the longer decode times). Anyway, that is a genuine problem with PM. But Kevin and others have shown us how to feed CTCSS to the crystal and thus frequency modulate the CTCSS, which is an excellent way to handle the problem.   73, Bob, WA9FBO 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.