Rick and All,
Sometimes we forget the basics in HF digital communications.
After WWII the U.S. military ask Stanford Research Institute (SRI). to find out what the highest baud rate was that could be used on HF and what the best baud rate was. Harris RF Comm Gp in Rochester, NY at one time had a complete copy of the full report. The report suggested that 100-120 baud was the max baud rate to use and that the best baud rate (for all frequencies between 3 and 30 MHz) was something around 50 baud. In the mid 70's the DoD ask the question...what is the best single baud rate to use for HF data communications. The rate that most vendors came up with was 45.5 baud.
Higher baud rates get "whacked" by HF skywave propagation. 45.5 (50) baud seems to be the best average.
So modes that use higher than 50 baud will take some "hits" from skywave HF propagation. And baud rates less than 50 baud don't provide much improvement in signal quality vs throughput.
Thus in evaluating a mode, look at the modulation rate (baud rate) as one of the evaluating criteria.
Walt/K5YFW
-----Original Message-----
From: digitalradio@yahoogroups.com
[mailto:digitalradio@yahoogroups.com]On Behalf Of KV9U
Sent: Wednesday, December 07, 2005 10:50 PM
To: digitalradio@yahoogroups.com
Subject: Re: [digitalradio] Digest Number 1722
Hi Bob,
Good questions. But I don't think that the new modes are all that
frequent. Maybe only one every three or four months or so:)
Many of the modes will not be used much unless they are available with
different software packages. If they are only available one product, it
will be difficult to sustain any kind of critical mass. Over the years
there are a number of orphan modes as newer modes came along that worked
better or had some feature that appealed to users of the mode. For example:
- Kantronics G-TOR never really went very far being a proprietary mode
- Some modes could not deliver, e.g., 110 baud ASCII in lieu of 45 baud
RTTY, even though it had the full character set but could not do well
with HF conditions - Even worse was HF 300 baud packet. Still used by a
few in what appears to be a make believe HF network, but has extreme
problems with propagation on HF
- AMTOR was the first HF ARQ mode that was very popular for a while but
did have stringent rig timing requirements and has mostly only been able
to be used with hardware interfacing although there is a Linux based HF
sound card mode.
-Clover II was expensive proprietary equipment and was not really good
with poor conditions. Clover I (also invented by Ray Petit [SK]), was a
hardware design not practical for many but was a concept that was later
possible to develop into new digital modes due the the increasing power
of computers.
Now we have newer modes, mostly sound card types, ofen more for casual
keyboard use, that work very well for many conditions. Without looking
at proprietary modes or modes on only one fee based product:
-PSK31 for casual keyboard chatting under moderate conditions and with
extremely narrow bandwidth and can handle -10db S/N or slightly worse
-PSK63 for twice the speed and a bit less tolerance for conditions
-MT-63, very robust down to about -10 db S/N with the narrower 1K mode
and with up to 200 wpm throughput with the 2K wide mode. Currently the
fastest sound card mode for difficult conditions, especially multipath.
The best non-proprietary HF mode at this time for messaging traffic due
to the relatively high speed, but overkill for most keyboarding
-MFSK16, more robust with weak signals and can work down below -15 db
S/N ratio and can handle some other poor signal issues such as doppler
and multipath
-Olivia, seems more able to handle weak signals although similar to
MFSK16 but requires much wider bandwidth to handle the more difficult
conditions
Most other modes are not really better than these from what I have seen
but some may have specific likes about some of them and may not be
universally available to ham operators.
73,
Rick, KV9U
Bob DeHaney wrote:
> I've been following the list now for some months. I'm an OOT first
> licensed
> in 1960. And I am really interested in digital communication as I've
> earned
> my living up to now (retiring) as an EE working with networks.
>
> My question is: Does anyone ever ask: "Do we need another digital Mode?"
> It seems a new one is on the list about every 14 days. It takes me
> about 30
> minutes to figure out which mode I should be decoding!!
>
> I am seeing mode proliferation that looks like it's being done to say
> "Look
> a new mode and it does something better than another mode, ...but not
> everything, some things it does worse...
>
> It's like the feature proliferation in mobile phones, Geez I just want to
> telephone with the thing and none of them can do as good a job as a real
> camera or a real MP3 player. But they are more expensive and if you
> use the
> features to send pictures etc. the provider is making a LOT of money.
>
> 73,
>
> Bob DJ0MBC/WU5T
>
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