[aprssig] Re: Sending messages from the keyboard.

Stephen H. Smith wa8lmf2 at aol.com
Thu Sep 15 00:39:54 CDT 2005

bruce.coates at sasktel.net wrote:

> Hi
> A fellow ham has asked whether he can send an APRS message using just 
> a plain TNC-2 and simple terminal program such as HyperTerminal.
> I'll be operating a station at a search and rescue command center 
> under VE5BNC.  The other ham will be operating a portable station with 
> a TNC-2 and a laptop running a terminal program under the call 
> VE5RY-??.  His home station will be setup up for digipeating under the 
> call of VE5RY.
> The question is, "What exactly would he type into his terminal program 
> so that it creates and sends an APRS message to me either direct or 
> via the digipeater?"
1)  If his station IS the digipeater, then there is no distinction 
between working him direct and via the digi.  Using the digi (or putting 
the digi in your path) is pointless, unless third parties somewhere 
outside your own direct range are listening.

2)  With his TNC in command mode, set  MYC inALL to his callsign, 
MYALIAS to "WIDE1-1" or some such for digipeating, enable the digipeat 
function, and set his NONPROTO path to "APRS".  Since this isn't a true 
APRS-savvy WIDEn-N dig, but rather a dumb classic packet digi, you will 
have to set YOUR path to exactly match his to get digipeated;   i.e. if 
his alias is set to WIDE1-1, you have to set your path to WIDE1-1 (or 
his actual callsign VE5RY). 

3)  Command  the TNC into non-connected conversational mode (usually 
something like "CONV" at the prompt) after making the settings, so that 
it will transmit every time he types a line of text and hits enter 
without being connected.

4)  Transmit a few messages and beacons to him from your own APRS 
client. Transmit a posit in normal human-readable APRS (not compressed) 
format.    Have him turn on logging (text capture) in his terminal 
program and save some of these into a text file.   Most TNCs in monitor 
mode display the headers (to and from calls, paths, length, time, etc) 
on a separate line from the packet payload.  You only want the payload 
part of the packet. 

5)  APRS posits, status reports, and messages use a very precise format. 
A single typo or omitted space will break the transmission.  Use the 
logged samples as templates to construct his own transmissions by 
editing the samples, then copying and pasting  them into the terminal 
program transmit buffer.      (Use the usual Windows cntrl-C to copy a 
high-lighted block, then cntrl-V to paste it into another window.)

6)  Have him take one of your posits and edit the lat/long values (and 
possibly the symbol codes and comment field) to match his QTH.  Save the 
revised string into a text file, or assign it to a macro key in the 
terminal program. [Most terminal programs have programmable keys to send 
canned strings of text normally used for passwords, network logon 
sequences etc.]  Anytime he wants to send a posit,  copy and paste the 
modified string into the terminal program transmit buffer and hit 
<ENTER>  (or hit the macro key) . 

7)  Edit the sample posit several times, entering a different lat/long 
each time corresponding to points on a highway, change the symbol code 
from a house to a car.   Save these altered strings to successive lines 
of a text file.   During the demo, have him copy, paste and send one of 
these every few minutes to simulate a mobile in motion.   
     Or, ahead of time,  log your own real mobile moving around.  If he 
pastes only the payload of your posit packets into his send buffer,  the 
TNC will  add his callsign and path to them, making them look like HIS  
(virtual) mobile.  Just don't let the cat out of the bag by leaving your 
callsign, email address, etc in the comment field of the packet!

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com

"APRS 101"  Explanation of APRS Path Selection & Digipeating

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