Rick,
We have four parallel efforts right now. One is to adapt PSKmail for better TTY
operation as opposed to mailbox operations, another is to embed ARQ in fldigi,
another is to rewrite FMpsk to improve decoding and orient it more toward
decentralized Emcomm communications, and lastly, to write a new program using
VB.net (I just received my free copy!) with the PocketDigi code and add ARQ and
form handling to that. We are furtherest along with the PSKmail modification at
the moment.
Our own tests confirm that DominoEX is the best choice for performance,
especially on HF using NVIS antennas, but the latency of DominoEX requires a
modification of the ARQ protocol (probably multiple <SOH> in each frame) to
overcome that. In addition, DominoEx is much wider, and therefore fewer signals
can occupy the same passband for multichannel display. When you add ARQ, the
multipath problems we experience sometimes with PSK63 on VHF are negated by
just repeating frames and this works well in practice because the multipath
cancellations are short-lived and throughput is therefore not reduced very
often. Even DEX/FEC is not the answer, as only ARQ will guarantee completely
error-free transfers. Note that a single wrong digit in a phone number can
render an entire message useless!
Our Linux effort is directed at adding fldigi or PSKmail on a "live" CD using
Puppy Linux. Several of our VHF net members, including myself, already use
Puppy Linux with fldigi as a "live" CD on Windows machines on our twice-weekly
net, and there have been no problems at all. This helps compensate for not
having a Windows application, but not completely, as there still are hardware
recognition problems with all Linux distros that have already been solved under
Windows, so a Windows version is still planned.
Although our focus is on VHF applications, what we are doing is also applicable
to HF, of course, and especially using DominoEX, but we just have not had
enough time yet to test a modified protocol with DominoEX for HF use. I got as
far as showing why the PSKmail guys were never able to link using DominoEx,
even though it is included in fldigi and PSKmail. Once we have completed our
demonstration application for VHF, we will turn our attention to the HF
application.
Practically, our VHF net members prefer PSK63 over DominoEx because it is
easier to manually tune, even though DominoEX has a broad mistuning tolerance.
There is also a significant improvement in using horizontal polarization
compared to vertical polarization (RCA established this years ago for TV and
that is why TV signals are horizontally polarized). Then, using PSK63 instead
of FM results in another huge improvement in range. There will be a QST
constructions article in coming months for a horizontally-polarized 2m antenna
that equals the performance of a 5-element beam, but over a 160 degree
beamwidth and is bi-directional in addition. Using this antenna, I am able to
work over 100 miles to a 5-element beam over flat country. So, the comparison
in range to FM repeaters is somewhat like comparing apples to oranges.
All this may seem strange, but we are trying hard to "think outside the bun"!
;-)
2a. Re: Comments to ARRL on New Digi Protocols
Posted by: "Rick" [EMAIL PROTECTED] kv9u
Date: Thu May 31, 2007 7:14 am ((PDT))
Skip,
Sounds really interesting. Isn't much of this is available right now
with Linux, on PSKmail? However it is not available on MS Windows OS
which is what 95+% of hams use worldwide for now. It would seem that
adoption will be low until we have cross platform capability.
