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[aprssig] PropNET Lessons Learned [was: 6m MS network (aprssig: to exclusive) PerformanceMonitoring!]

Bob Poortinga aprssig.10.bobp at xoxy.net
Fri Jan 4 16:13:56 UTC 2008


On Jan 4, 2008 8:22 AM, Robert Bruninga <bruninga at usna.edu> wrote:

> I think the major difference is that MS requires gain antennas
> (Beams).  The signals are there, but are weak when they break
> through.  Without 10 dB of antenna gain, there is a drastic
> affect on decodability.  But people are not going to have lots
> of beams for 6m.  BUT, all it takes to get 12 dBi of
> unidirectional gain is about 120 feet of wire strung as a long
> wire in the initended direction.

Bob et al, I have been running 6m MS with WJST for about 4
years now.  Here are a few of my observations:

Gain antennas are nice, but not required.  I made a number of
contacts using a simple vertical loop and 100 watts.

During normal (non meteor shower) periods, bursts are usually
short; normally in the range of 200ms to 800ms.  At 441 baud
(WSJT FSK441), that means about 15 characters or less.
Longer bursts do occur, but are less frequent.  Forward error
correcting protocols were tried (FSK441B and FSK441C) but
were found lacking due to short length of bursts.  Just how
reliable 1200 baud AX.25 will be is unknown.

Sporadic-E and Tropospheric Ducting occur more often
on 6m than people realize.  There will be times when two
distant stations, transmitting at the same, will be interfering
with each other.  This is especially true in the southern
states.

One last question: if the main purpose of this 6m APRS
network is to gate email from disaster areas, why isn't HF
the preferred option?  Do we need another HF frequency,
maybe on 40m, dedicated to APRS?

73 de
-- 
Bob Poortinga K9SQL
Bloomington, IN  US




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