[aprssig] APRStt (DTMF) at Hamvention

Bob Bruninga bruninga at usna.edu
Sun May 10 16:05:17 EDT 2009

> [To use APRStt at Hamvention], as I understand it, 
> (a) I've got to set up my VX-7R [DTMF memory]
> (b) I've got to carry a paper grid reference 
> (c) I've got to remember to update my  
> position every 100 feet, so that anyone who 
> happens to be near a display can see where 
> I am, provided they know my callsign.  

Basically, APRS is not a tracking system.  It was never designed to provide the bandwidth for continuous tracks on everyone or even on ANYone.   That is the great missconception about APRS and what burdens the network with unnecessary tracking data when 99% of everyone could care less where 99% of everyone else is.

APRS is a communications system to facility communications between hams needing to communicate without apriori knowledge.  There is no reason to transmit your position, unless there is a specific reason why you want someone else to know where you are at that instant.  Or to give them in the blind, your operating frequency.

But if  you stop for an hour in a forum, or stop for 30 minutes under your club tent, or at the food court or the Bar, then you might want to send out a posit to let your buddies know where you are.  In this case there are only four XY coordinates of interest to you.  The one at your club tent, the one at the food court, the one at the bar bar, and the one at the Forums.

> Alternatively, someone who wants to know 
> where I am can call my callsign on an 
> agreed frequency.  

That works too but requires some inconveniences too. 

1) you must have a pre-arranged freq
2) the freq must be relatively clear of other chatter
3) No opportunity for meeting others without #1,#2
4) the recepient must be listeing FULL time
5) Must have his volume turned up
6) Must be paying attention to ALL voice traffic so that he can possibly hear his own call amongst the othres

So both methods have advantages and disadvantages.

An advantage of APRStt is that it is global.  Once you send out your DTMF callsign memory, anyone in the World of amateur radio that needs to conatact you can not only see you are in dayton (or timbucktu), but can text message you.  Again, not that anyone would, but if you ARE expecting someone at a distance to contact you, this gives you the means to be contacted.

For special evnts like marathons, etc.  The two digit numbers you may use for your position can be the mile-marks.  This lets a VIP shadow, or SAG wagon or any other non-APRS moving asset occasionally report what station it is near (not while moving of couse0, but when he shifs from one station to another.  This eliminates a lot of voice traffic from an already overloaded voice net.

> Please explain what I have failed to understand...

Hope that helps.

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