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[aprssig] 9600b UHF APRS IS THE FUTURE OF APRS

VE7GDH ve7gdh at rac.ca
Mon Oct 9 16:24:29 UTC 2006


Gregg W5GGW wrote...

> The "better" coverage of VHF is, in fact, the
> bigger problem the current APRS network has.
>
> Cellular and wide area network technologies use higher
> frequencies and lower power to simplify life and create a
> more dependable system, not to cause themselves to
> spend more money on more cell sites.

And Bob WB4APR had written earlier...

> VHF is 9 dB better than UHF for omni antennas (think mobiles)
> AND it has less multipath and fades. So APRS at UHF may have
> practical applications, but serving as a general distribution it will
> never be as "good" as VHF.

Good postings by both! I have been suggesting for a long time
(ummm... better let me re-phrase that; for a couple of years or so!)
that we need to operate more like the cellular network. Instead of more
"big" digis up at a higher elevation, we need more "small" digis at least in
the populated areas with less coverage. Perhaps densely populated areas
could work on a low powered UHF network for operation in the concrete
jungle. The existing VHF infrastructure could remain in place or be pruned a
bit. Keep the high elevation VHF digis for operation away from densely
populated areas, consider removing a few high elevation digis if they are
causing more harm than good, and encourage 1200 bps UHF APRS for the
densely populated areas. This concept would work better if the stations in
the densely populated areas reduced their power when they are in an area
with a large number of low elevation digis. The ideal situation would be
radios that are both frequency agile so they can move seamlessly between
densely populated areas with good UHF coverage and out in the boonies where
they need to change back to VHF and up the power a bit. Even better, the
output power would automatically adjust itself either based on the strength 
of received signals (from digis only) or upon confirmation of being 
digipeated.

Lofty goals, and it won't happen overnight. At the very least, we could work
on moving some of he high elevation digis near populated areas to lower
elevations and encourage building of UHF digis in the same densely populated
areas. Users could be asked to stick to low power when needed. These can all
be done without fancy frequency agile radios that automatically adjusted
their power output.

I'm not putting down 9600 bps packet. I've never even owned a 9600 bps TNC
(until now... just received a beta TT4 the other day) so don't have any
first-hand experience with the vagaries of 9600 bps on RF, but I'm all for
developing equipment for faster and more robust packet connections. There
are those experimenting with 9600 bps packet, notably in the Seattle / Puget
Sound area, but for general use, it sounds like there are advantages of 1200
vs 9600 and there are advantages on VHF vs UHF, but both will have a place.
It's just time & money, and the enthusiasm for development new equipment.
I'm hoping the commercial manufacturers don't abandon us, but I'm
increasingly getting the impression that development of "leading edge RF
communications" is again putting the ball back in our court instead of
leaving it up to the commercial manufacturers telling us what they can
provide.

73 es cul - Keith VE7GDH
--
"I may be lost, but I know exactly where I am!"





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