[K3PZN-List] New NBFM spacings & BW?

[Matt Smith]

On 12/02/2010 12:49 PM, Blank, Dave E wrote:
> So if 25KC bandwidth is =/- 5KC or Where we are now!
>  and  12.5KC  bandwidth is +/- 2.5kc 
>  than 6.25KC bandwidth is  +/- 1.75 Deviation. Or where they want to end up.
> That isn't much talk power! But remember this would be digital, so your existing radio is still sending analog voice. Most newer commercial radio's are being sold with 12.5 KC bandwidth. Many are advertised to be 6.5KC capable. Many of the reduced modulation/bandwidth radio are actually using a Vocoder (A Device using a look up in a table to manually reproduce human voice) to give you the message! So if they (the FCC) want to convert the HAM to a lesser level of Modulation, say 12.5 than you could get by with just turning your deviation back. But to be able to go to the 6.25kc level you would really need the vocoder making your older radio's obsolete and unusable. 

Actually, 5 kHz deviation with audio response to 3 kHz winds up being about
16 kHz of overall bandwidth. In order to squeeze analog FM into 6.25 kHz and
retain an audio response to 3 kHz, you're left with room for 125 Hz of
deviation, which might as well be AM. This is where digital voice modes and
FSK come into play.

As for digital voice that's not patent encumbered, codec2 looks promising.
http://www.rowetel.com/blog/?page_id=452

--
Matt, AB3JU