Hi Ed.
I'm rarely on in the evenings and mainly on Saturday and Sunday afternoons and
on holidays...and on rare occasions as K5STB/P on Saturdays.
UR Questions...
1) Can you suggest a reference on HF propagation that may show
distributions or histograms of fade depths, durations and bandwidths?
No...I generally use the NVIS HAP charts from
http://www.ips.gov.au/HF_Systems/7/1/1
Realtime fade depths, durations and bandwidths are going to change so
much that you
would probably have to be on-the-air at both ends of a path to
determine this for any
one band of frequencies.
2) For the examples of military equipment you gave, did they use
voice bandwidths (~2.5 KHz) or were the bandwidths larger?
Most has 2.7 KHz receiver bandpass filters or slighly less. CW filters
were 400 Hz and AM filters were 6.x KHz. Most units used AME-USB with
re-injected carrier so wht bandwidth was the same as SSB
3) With military communications I expect that voice quality and
accuracy of the communication is essential. For ham weak signal
applications where accuracy is not a life and death matter, can we
gain any performance by trading codec data for FEC data? If voice
quality at 2400 bps is considered acceptable for military
applications, can we get better SNR performance with useable voice
quality for ham applications at codec data rates less than 2400 bps
with stronger FEC?
You would think that voice quality and accuracy would be essential and
in fact it is. However, the reason they sent from 1200 baud to 2400
baud
for DV was just that and when signal levels were good enough, they used
4800 BPS.
The robustness for the 2400 bps DV wasn't all that good...something
more than
a + 10 dB SNR was required. A more robust DV that would work with SNRs
of
0 to -5 dB would be great...but then you could use 4800 bps DV at +10
SNRs.
The qualitity of the AOR DV units is nice...very clear...I don't think
that
part needs much imporvement. However, they require such a high SNR
that they can't
be considered very robust.
Walt/K5YFW
-----Original Message-----
From: [email protected] [mailto:[EMAIL PROTECTED]
Sent: Wednesday, October 11, 2006 3:34 PM
To: [email protected]
Subject: [digitalradio] Re: Digital Voice: Some thoughts after one week.
--- In [email protected], "DuBose Walt Civ AETC
CONS/LGCA" <[EMAIL PROTECTED]> wrote:
>
> I've heard DV using LCP-10 and a 16 tone modem as well as a 39
tone modem at 1200 bps...it sounds robotic at best. But that could
have been just the systems used (ANDVT/Mil-STD-188-110)
>
> Walt/K5YFW
Walt,
Thanks for your very interesting and informative comments. I would
be very interested in meeting you on the air for an extended
conversation on the subject. We should be able to connect on 40M or
80M in the evenings. I often monitor 7295 +/-. I can also be
reached on EchoLink.
Some of the questions I have are:
1) Can you suggest a reference on HF propagation that may show
distributions or histograms of fade depths, durations and bandwidths?
2) For the examples of military equipment you gave, did they use
voice bandwidths (~2.5 KHz) or were the bandwidths larger?
3) With military communications I expect that voice quality and
accuracy of the communication is essential. For ham weak signal
applications where accuracy is not a life and death matter, can we
gain any performance by trading codec data for FEC data? If voice
quality at 2400 bps is considered acceptable for military
applications, can we get better SNR performance with useable voice
quality for ham applications at codec data rates less than 2400 bps
with stronger FEC?
Is there anyone reading this thread that could develop additional
experimental modes for WinDRM?
Ed
WB6YTE
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