[FARC] APRS Map, Packets, & Internet

Tue Sep 18 09:42:31 EDT 2007

I wanted to share a little more about APRS with the group.  I can't
add a picture attachment to a FARC list e-mail, so here is a link.
http://picasaweb.google.com/joseph.durnal/General/photo#5111526191564117058

On this map you can see the N3KTX-2 digipeater which is up on the
mountain.  KB3ONM, KA3HJC, & NE3R home stations.

Yellow, green, & dotted purple lines are trails for mobiles.  You can
see KB3LVU took a trip from Charles Town to Frederick and back,
KC6ETE-9 coming down I-70 from the west, & N3VTV around New Market.

FMH isn't an actual station, but an object that is transmitted from my station.

These maps, known as tiger maps, can get really detailed down to the
street level.

What makes all of these little pictures on the map?  Packets of date
on the air waves of course

Here is an example of my home station packet:
NE3R>APX191,WIDE2-1:=3922.21N/07726.12W-HG3000No Traffic

The first part is the originating station, NE3R>
Next is the destination path, the APX191 represents the software I'm
using, and WIDE2-1 tells digipeaters that the packet should only take
one hop.
The = is a little known bit that indicates that I can receive messages
This is the lat/long of my position 3922.21N/07726.12W, the / between
also helps determine what icon APRS programs should display.
the - just after the W is the second part of my icon, making my icon
/- which is for the little house.
The next part HG3000 stands for the Power Height & Gain of my antenna
system, which is pretty low.
Finally, there is room for a free text field.

Here is an example of the FMH packet transmitted from my QTH:
NE3R>APX191,WIDE2-1:;FMH *172133z3925.41N/07724.93WhFrederick Memorial Hospital

The first part is the same, as is the path.
It changes at FMH, which identifies the object.
The * denotes that the object is new (it is new on every transmission)
The next part is the time, which I should change to 111111z to make it
a permanent object.  Some objects, like storms and tornadoes are time
sensitive and expire.
Following the time is the position 3925.41N/07724.93W, again with the
/ being part 1 of the icon.
The h is the second part of the icon, and /h is for hospital
Finally, there is the free text field.

Here is in interesting packet:
NE3R>APX191,N3KTX-2*,WIDE2:;FARC-MTG
_180508z3925.64N\07725.96WhFrederick ARC Meeting Monday

It is basically the same as the FMH packet, but notice the _ before
the time, that means that the object has been deleted and APRS clients
should remove it from their screens.

Now for a message packet, and its corresponding acknowledgement:
NE3R>APX191,WIDE2-1::KB3NAI-2 :Good Morning David, I'm off to work
now, no mobile APRS yet!{0N}

I sent a message to David this morning.  The pattern continues early
on, origination station and path.  Following the :: is the
destination, then following the next : is the message.  The last part,
{0N} is the message identifier.

KB3NAI-2>APK101,N3KTX-2*,WIDE1,WIDE2-1::NE3R :ack0N}
When David's radio received the message, it sends and acknowledgement
the message identifier that was at the end of the message packet, in
this case, 0N.  That tells my APRS software that the message was
received and there is no need to keep retrying.

You'll notice that David's path is a little different, you see
N3KTX-2* which is the digipeater that my station actually heard
transmit the packet.  The WIDE1 used to be WIDE1-1 when it was
transmitted, the -1 was dropped and replaced with N3KTX-2*, the
WIDE2-1 means that the packet will be retransmitted one more hop by
other digipeaters.  In this case, I didn't need the extra hop to
receive it.

This got a little longer than I expected, but it is all good
information.  You may have seen me with the 118 page specification
last night, well, this is the abridged and truncated version of that!
But I have just a little more.

We mentioned the internet last night.  While APRS doesn't need the
internet to work, the internet collects a lot of APRS information.
The website that has it all is called findu.com.

http://www.findu.com/cgi-bin/find.cgi?call=NE3R

Findu.com isn't very user friendly, so some others have made good
front end web pages that make it easier.

http://www.wulfden.org/APRSQuery.shtml

An interesting query for all APRS stations near a zip code:
http://www.findu.com/cgi-bin/near.cgi?zip=21703

This is an interesting real time site:
http://aprs.he.fi/
It can really use up a lot of computer memory if left on to long.

Ok, I can't type any more (started this last night!!!)

73 de Joe NE3R