[aprssig] Packet Node on 144.390 ?
jmaslak-aprs at antelope.net
Sun Sep 10 22:51:40 CDT 2006
On Sep 10, 2006, at 9:30 PM, Daron J. Wilson wrote:
>> In an area with one or two or three active users total - it wouldn't
>> be cost effective to build two separate systems when one would
>> work just fine. Any more users and activity would make sense
>> to build a separate system to carry the additional load.
> In that small of area, they could just run on the voice repeaters,
> it's just
> sharing bandwidth right?
I'll add that the repeater may be the more efficient option for
emergency communication if all the stations can hear it effectively,
more then two stations are communicating, it has a reasonable TX
Delay, and at least one station on channel can't hear at least one
Repeaters solve many of the hidden transmitter issues. The only
major issues using them are to ensure the repeater is "flat" (doesn't
emphasize certain tones) and that the users use software carrier
detect. The problem with software carrier detect is if a voice user
does try to use the repeater the packets won't detect that as an
active station, and also the repeater's ID will clobber a few packets.
Hidden transmitter issues are ignored far more often than they should
be. Channel utilizations of 60% or higher are perfectly reasonable
even with a reasonably large number of active stations - IF everyone
can hear everyone. If someone can't hear someone else (but maybe
some node or central station can), you might be lucky to get a tenth
of that. That's because neither stations realizes it's clobbering
another's transmissions. (with APRS, this is even more likely since
most stations are bad packet stations - they are low power, often
mobile, with sometimes less than ideal geographies, and large area
digis that can hear other large area digis that their users cannot
hear; Adding connected mode packet to the mix will make things
miserable for both APRS and connected-mode communities, as neither
will work right)
It's also a lot less important to have good emergency packet stations
in this configuration.
Surely there is a nearly unused voice repeater in nearly every area
of the US (and possibly elsewhere in the world).
But of course no one likes to hear packet on their voice repeater,
but it's fine to jam APRS! ;) So it probably won't even be
considered a reasonable option. But neither should using 144.39.
Besides, if you have a digi site for 144.39 that doesn't have any
70cm equipment already, all you'll really need to add a second digi
is a radio (cheap for 1200, more for 9600) and TNC (cheap for 1200,
more money to do 9600). And you can go 9600 instead of 1200 - so
that you can increase the number of users and amount of information
transmitted. Heck, you can even build real packet nodes fairly
easily rather than just relying on "dumb" digipeaters.
If the organization isn't interested in using voice repeaters or
building new permanent digis, why not build a temporary digi? One
that fits in, say, an ammo can and can be carried by hand to a tall
building or left in a car parked on a mountain top, in an area
sufficient to provide the coverage needed during the disaster? (I
know where I live there are plenty of areas without good coverage by
digis on 144.39, anyhow, and Murphy says that those are the most
likely areas to need communication) Build 2 or 3 of these portable
boxes as true nodes and you could have a mobile network that you can
use not only in your local area, but also in another area if another
Katrina or something happens. Heck, it might be a fun project!
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