I have
a few thoughts on new modes and existing modes.
We do
have several choices depending upon the conditions and the intended use. PSK31
works reasonably well for casual contacts where you are not too concerned with
taking a few hits. To me it is narrow band, improved RTTY.
And
when the going gets really rough we have MFSK16. Possibly Olivia, but I am not
sure if there is that much difference for comparable BW. I have found
that if Olivia is used with narrow BW, it is not competitive with MFSK16
from my testing on 80 meters.
Speaking of 80 meters, does anyone try using these modes under the most
difficult conditions? If so, what do you find consistently works the best? I
find it very difficult to ever find any digital stations on that
band.
If you
need speed, MT63 is the best game in town, thus far, but I have had cases
where you could not copy that mode on under difficult conditions, yet MFSK16
worked fine.
The
Chip mode seems very easy to tune but since it runs a very high baud rate, will
be a problem with ISI issues not unlike 300 baud packet. However, the FEC
helps a great deal. I have been tentatively monitoring some
of the contacts, and it does not seem to perform as well as MFSK16 and
it is not all that fast. I do print hits with moderately good signals. Perhaps
it is useful as a comparison to different schemes of modulation and what does
and does not work?
What
we do need the most from an emergency communication perspective is an
error free (ARQ) sound card mode that optimizes maximum speed for a given
channel size. Ideally, it would be able to have some ability to be agile to
conditions and have some fall back modes to handle worst case situations. Even
if fairly slow. The new Linux mode can do this, however having a cross platform
would be instrumental in gaining popularity here in the U.S.
By the
way, I wonder if many developers are seriously looking at the MONO framework to
make cross platform products.
Upon
reading some of the messages in the CHIP64 newsgroup, it appears that there is
some interest in making the mode ARQ. I wonder if that is a good choice though,
considering the high baud rate?
I
still would like to see an ARQ mode optimized for more difficult HF
conditions based upon what we know about ionospheric effects. It seems like
having a BW selectable mode of perhaps 500 Hz minimum to 3 KHz maximum, running
at a baud rate up to maybe 300 max and fall back to 100 and then to 50 for sure,
(and no lower) would be one of the more robust sound card modes possible.
Similar to Pactor, it could always connect at the narrow BW and at 50 baud and
go from there so that we would not have so much incompatibility as we do now
with modes that can operate on different speeds and BW.
In the
past, the concern was that the timing of computers made it difficult to do this.
While it may never be possible to have fast turn around ARQ modes
such as Pactor, the development of SCAMP has proven how well a "pipelined" mode
can work. Amazingly well. The downside is the latency, but that
is seems an acceptable tradeoff unless you are running a quick
casual keyboard to keyboard contact.
With
all the developments in the past year or two, it seems like the bits and pieces
are there for the taking in order to develop a real solution to what we need for
messaging.
73,
Rick,
KV9U
-----Original Message-----Hi Y'all...Whats up with all of these new keyboard to keyboard digital
From: [email protected] [mailto:[EMAIL PROTECTED]On Behalf Of smar_68
Sent: Friday, September 16, 2005 22:36
To: [email protected]
Subject: [digitalradio] Keyboard to Keyboard
modes? I see now we have "Chip 64". Are we trying to squeeze as much
sensitivity out of our soundcards as we can get? My point is this...it
is impossible to re-create a signal when the QSB reaches the point of
wiping out the signal entirely. In my view, I have only used PSK31 and
MFSK16, and both of them fail when the QSB reaches a certain point. We
should not expect miracles from every new digital mode that comes
along. Just my opinion. I will stick with PSK31 and MFSK16 for the
foreseeable future. Am I missing something here?
Steven Renaud
VE3ALY
The K3UK DIGITAL MODES SPOTTING CLUSTER AT telnet://208.15.25.196/
More info at http:///www.obriensweb.com
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