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[aprssig] APRS experiment along I-40, mapping vs. voice alert vs. local info

Robert Bruninga bruninga at usna.edu
Tue Jul 13 21:20:41 UTC 2010


Great report!

> I haven't been a fan of Voice Alert and 
> never really tried out anything with local info...
> ... from Columbus, GA to Los Angeles, CA....
> ... part of APRS (mapping, tracking) worked fine...
> Local info... I may have seen one or two announcements...
> Voice Alert failed completely...  Over a road 
> distance of 2,200 miles... not one squawk...

Welcome to the club! 
It is so frustrating to be driving past so many other ham
operators and so many APRS mobiles and not be able to even know
they are there or being able to contact them...  Statistically,
one in every 500 cars is another ham.
Lets assume that 10% are running APRS.  This means one in every
5000, which on an interstate is about once every 2 hours or so.

So, of those APRS mobiles that passed by,

How many were you aware of?
How many contacted you or struck up a QSO?
How many did you try to contact?
Did you hear any calls on 52?

You didn't mention any and it does not surprise me.  This
matches my frustration on my 1800 mile round trips down I-81
from Maryland to Alabama and back through a WELL CONNECTED APRS
system...

But if those other APRS mobiles on the open road had been
running APRS Voice Alert, there would have been a half dozen or
so a day of enjoyable interesting contacts.

> Honestly, I think that it's just not as interesting to 
> operators as some may have us believe.

Yes, because so few are transmitting so there are so few to
hear...

The number one complaint we hear each time we talk about Voice
Alert is from the nay-sayers who don't want to hear all that
Packet Racket.  Which is about as dumb of an excuse as there is,
since you just demonstrated that there are NONE to hear over
2000 miles across country, because no one is transmitting it!
Its just all the naysayers that have never tried it want to
complain about a problem that does not exist.

Its like anything in ham radio... If no one call's CQ, then the
band is dead and there is nothing to do.  

> I was on the air for 14-16 hours a day...
> beaconing my position once every three minutes...

Ah, there is a problem.  At a combined speed of over 2 miles a
minute, you only have one chance every 6 miles to even be heard
by someone else.  And the simplex range mobile-to-mobile is
usually less than that.  For Voice Alert, you should always be
beaconing at a 1 minute rate.  This gives you a possible 3 hits
per other person you pass.

But to keep the QRM down (even lower than your 3 minute rate),
that is the power of Proportional Pathing designed into the
D710.  It transmits a local simplex direct packet once a minute
(for nearby mobiles).  But only via a WIDE1-1 once every 2
minutes, and only via the wider area 2 hops once every 4
minutes.  This is less regional QRM than a fixed 3 minute rate,
but gives you a far, far better reliability at voice alert and
close-in nearby tracking.

> Surely if it were as important and popular 
> as we hear then I should have heard at 
> least one packet burst come through.

You'd think.  But that is why we talk about it so much.  It's a
fantastic system, just most APRS operators are clueless to its
value on the open road.

Spread the word.  It works when people use it.

Same for local info.  So many local areas just have not gotten
off their butts to put out the info.  Again, if no one is
transmitting it, then there is nothing to do...

Bob, WB4APR





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