[Elecraft] K3 Digital Voice Mode - our future?

[Matthew Cook]

If you take a closer look at the spectral bandwidths of the current crop of
digital VHF/UHF voice systems and compare them to 10k1 NBFM I think you'll
be surprised.  Unless govt agencies start racking and stacking digtal LMR
systems without guard bands then there is no clear advantage.  The
technical requirements of each receiver goes through the roof with 10k1
systems as it.  However there is a strong desire from government agencies
to move toward encrypted communications, which is very easy with digital
LMR; basically you get it for free.  This does not relate to the amateur
service.

In terms of Digital voice replacing SSB that has a very long long way to
go.  In truth SSB is very difficult to beat in terms of spectral
efficiency.  SSB puts just enough power into the right spectrum for near
loss less communication.  When you try to stuff the equivalent power into a
low bit rate digital signal, the energy per bit is quite high, meaning
you've got to lower your bit rate substantially until the two powers (SSB
and DV) are the same.  At this low bit rate (<600bps) there is no avoiding
the donald duck or robotic voices at this point.  That pesky information
theory gets in the way.  Lots of great progress has been made in this
regard (i.e. Codec2), however it will be a while before the necessary
200-600MHz hard float DSP will be required in a K3S.  Besides I'm sure a
suitable retrofit DSP module can be squeezed in there somewhere when the
time comes.

73

Matthew
VK5ZM

On 18 September 2015 at 10:33, Robert Nobis <n7rjn at nobis.net> wrote:

> Take a look at the digital voice modes that are being used on the VHF and
> UHF bands: DMR, D-STAR and Fusion.
>
>
> Bob Nobis - N7RJN
> n7rjn at nobis.net
>
>
> > On Sep 17, 2015, at 17:49, Richard Fjeld <rpfjeld at outlook.com> wrote:
> >
> > I was in to freeDV a year or two ago, and it has a long way to go.
> Still, it did work.
> >
> > I'm told the bandwidth has increased since then from 1200 hertz to 1600
> hertz at present, which will be an improvement.
> > At 1200 hertz, voices sounded robotic in nature.  it lost sync often
> which may, or may not, have been due to the compression.
> >
> > I haven't heard of the FCC's having ruled on it's mode and/or where if
> permitted.  I haven't been keeping up with it either.
> >
> > Dick, n0ce
> >
> >
> > On 9/17/2015 1:00 PM, ae4pb at carolinaheli.com wrote:
> >> I'm wondering since Digital voice is replacing FM around the world how
> hard
> >> it would be to add another mode to the K3S? I'm not even sure what the
> >> standards are but one country just set the date to get rid of FM
> permanently
> >> and switch to DV.
> >>
> >> Jerry Moore
> >> AE4PB, K3S - S.N. 10324
> >>
> >>
> >
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