[CRAPRS] CRAPRS Digest, Vol 34, Issue 2

[Scott Haney]

From: Jerry Pasker <jerry at jerry.org>
>
> I don't know if I agree that it's possible to have too many digs in an
> area as long as the digis are properly coordinated.


That's the key point: coordination, or rather, the lack thereof. I think
the WIDE2 digis are coordinated rather well -- not a ton of overlap, good
coverage, reasonable settings. But we have a number of WIDE1 digis that are
not coordinated well, and with the recent uptick APRS interest, we need to
put a little thought into it.


>
> That's how it's supposed to work.  The digis are suppose to use the same
> settings/delays etc and the idea is that in a digi-rich environment, they
> all transmit at exactly the same time, and it's up to the FM capture effect
> to pick the strongest signal.  No channel bandwidth is wasted.  Years ago
> when I was getting in to APRS I read about this in the Los Angeles area,
> and that's how they solved their channel congestion.


> If I'm wrong, and I very well could be using an outdated viewpoint on
> this, please explain.  Or if I'm just plain wrong, please enlighten me so I
> can get up to speed on a better way of doing it.
>

That's not wrong, but it's not complete, I think. There are many digis out
there, and some are smart enough to not transmit if they detect that
someone else already is. For example, setting up a digi with a Kenwood D710
works this way. I do not know if there is a way to keep it from doing that.
(I suspect this feature is primarily there so mobile position beacons have
a chance to be heard by a digi. That's not necessarily good FOR a digi.) So
what sometimes happens is a digi queues up the packet, then waits for the
channel to clear. This results in multiple packets. I see this a lot in CR,
where my display will show the same packet coming from several different
digis.

I've set my gateway up with aprx, a Linux-based program that doesn't use a
lot of resources. My goal is to move it to a Raspberry Pi and let it run
all night (thus saving some electricity on my main machine). The aprx
program has a configurable "viscous delay," where it will wait a specified
number of seconds before digipeating. If it hears that same packet from
another digi, it drops it and doesn't bother. Coordinated WIDE1 digis could
just use different delays.

I agree wholeheartedly that the WIDE2 digis should just all transmit at the
same time. I'm thinking primarily of the little fill-in machines.


> I'll be moving my digi soon from one of the highest elevation homes in
> Monticello to one along the river, (6 feet above the flood plain)  loosing
> about 140 feet above mean sea level of altitude. Not even sure if it'll be
> able to make it to K0HAM-10 after the move, so I may be rethinking the
> usefulness or existence of my APRS station entirely.
>
>
> I feel your pain. My driveway is, as far as I can measure, is 16 feet
BELOW average terrain. So my 32-foot mast is not as impressive as it seems.
(It does have my squirrelly, new neighbors convinced I am a cop. I won't
disabuse them of this notion.) The other antenna is 16 feet up, which means
it is at 0 feet HAAT. I'm surprised I hear as many packets as I do.

Will the new location have any gating capability? That would still provide
a level of useful functionality. Based on what I hear from KF0VF, though,
getting an extra antenna for a digi on the new repeater tower seems
unlikely, but might be worth asking about.

rsh
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