[hpsdr] The problem with digital modes

[Brian Lloyd]

On Mon, May 12, 2014 at 9:33 AM, Clyde Washburn <k2ue at rochester.rr.com>wrote:

> ***** High Performance Software Defined Radio Discussion List *****
>
>
> I was expressing an opinion, after observing several 4-5 KHz wide digital
> signals on 20m keyed for long periods.  I appreciate that the use of
> “intelligence” is subject to debate. . .  But some folks seem to feel that
> all opinions must be judged on internet forums, and not merely countered
> with opposing opinions, facts if available, or ignored.
>
>
>
> Aside from the perception that it is cool, and new, and makes the operator
> feel very avante-garde, how is wide digital voice a huge step forward in
> spectrum utilization compared to say. . . AM?
>

Sorry, I missed that you were talking about DV as opposed to something like
PSK31.

I agree that, in that case, we really could use better CODECs. Nearly
everything we do in ham radio is based on narrow-band frequency-division
multiplexing. We could certainly stand a bit more time-division
multiplexing or, better still, frequency-hopping or CDMA spread-spectrum
multiplexing. I'm not going to hold my breath tho'. That would ensure that
the spectrum was used more efficiently.

Coding gain and energy-per-bit certainly comes into it. Also you have to
deal with the kinds of distortions introduced by the ionosphere. All of
this complicates CODEC design. It is not an easy problem at all.

-- 
Brian Lloyd, WB6RQN/J79BPL
706 Flightline Drive
Spring Branch, TX 78070
brian at lloyd.com
+1.916.877.5067
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