At 12/2/2005 16:36, you wrote: >I agree. DTMF is two sinusoids. You don't want the limiting action to >distort the signal. BTW this is also why you should use 3KHz as a baseline >on linked systems to keep the audio as linear as possible through >chain-linked RF repeaters. > >One thing that bugs me though is that the 2005 ARRL handbook says 5KHz RMS >deviation (appx 7.07 KHz) for NBFM. I beleive this is wrong.
Absolutely. In fact this is the first time I've ever seen the term "RMS" & "deviation" together. Some editor oopsed big time on that one. > I've always used peak-to-peak/2 setting on the HP8920 service monitor. The (almost) universally accepted method of expressing deviation is peak, which is equal to peak-to-peak/2. > > >Carson's rule states that channel bandwith is 2 times the sum of the peak >deviation and highest modulating frequency. If you use 5 KHz RMS deviation >with a 1KHz sinusoid, the channel bandwidth will be 2*((1.414*5000)+3000) >= 20.14KHz! >This ain't 16K0F3E. Here's the actual "Bessel breakdown" of the FM sidebands in dB, using a modulation index of 7.05 (closest I have to 7.07 in my spreadsheet): Carrier -10.46 +/- 1 kHz -39.74 +/- 2 kHz -10.54 +/- 3 kHz -14.95 +/- 4 kHz -16.78 +/- 5 kHz -9.29 +/- 6 kHz -9.32 +/- 7 kHz -12.44 +/- 8 kHz -17.56 +/- 9 kHz -24.21 +/- 10 kHz -32.10 +/- 11 kHz -41.04 +/- 12 kHz -50.90 +/- 13 kHz -61.58 +/- 14 kHz -73.00 So Carson's rule does pretty well here - the 20 dB BW is actually just under 18 kHz. Bob NO6B 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: http://docs.yahoo.com/info/terms/