LoS VHF/UHF comms was what I had on my mind, too... especially FM
simplex or repeaters. We have MANY more operators with VHF FM
capabilities as compared to HF or SSB VHF ops at our disposal and
VHF/UHF FM (simplex or repeated) would really be our bread and butter
for emergency radio communications in my part of the world.
In Western Pennsylvania, we're concentrating on the use of MT63 2k long
interleave, which really works fantastic on the line of sight paths and
on repeaters. We chose MT63 over the faster PSK250 and 500 for it's
ability to loose up to almost a full second of audio without missing a
beat as a result of the massive amount of FEC in the mode. BUT, we're
only utilizing about half of the usable bandpass of an analog FM signal.
It sure would be nice to double or triple our throughput and still come
close to maintaining the current reliability and robustness of MT63 2k
long. On FM, there is not the typical trade off on bandwidth vs accuracy
you have with SSB... we're just not fully utilizing the 4.5k usable
bandwidth at our disposal.
-Dave, KB3FXI
www.wpaNBEMS.org
On Tue, Sep 21, 2010 at 7:57 AM, Charles Brabham <[email protected]> wrote:
> Q15x25 mode uses fifteen PSK streams to return an effective 2500
> baud data rate - if all goes well. In tests on HF, Q15x25 was not
> very robust at all. It would work well with a strong, clean link
> but under typical HF conditions it slowed down considerably. In
> some conditions, HF Packet at 300 baud provided better throughput
> than Q15x25 mode at 2500 baud.
>
> As in the story of the tortoise and the hare, an emphasis on
> getting through can be much more productive than concentrating all
> effort upon simply going faster... Sometimes less is more.
>
The problem is, HF propagation through the ionosphere is NOT a
gaussian-noise-limited channel. Fast PSK does NOT usually fare well over
HF.
FWIW it would be good for LoS VHF/UHF communications.
If you are interested in fast datacomm over HF you need to study what has
been accomplished with PACTOR and WinMOR.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
[email protected]
+1.767.617.1365 (Dominica)
+1.931.492.6776 (USA)
(+1.931.4.WB6RQN)
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