Tips For Mobile APRS Users

NEW!!! The APRS MIC-Encoder will revolutionize mobile radio! It plugs into the Mic jack of any radio and puts your APRS-GPS posit on the tail end of any VOICE transmission. See MICE.HTM.

OVERVIEW: Although APRS on boats and aircraft already equiped with GPS or LORAN is obvious, it is IMPORTANT TO NOTE THAT APRS IS STILL VERY USEFUL FOR VEHICLES WITHOUT GPS TOO! Actually, the only stations that need GPS are the ones that are lost! For this reason, the first section of this file will discuss the use of APRS in a vehicle without GPS.

Note: Be sure to replay the DIGI-E, DIGI-W, or DIGI-SE.bk file before going on a trip so you can see where the digiepaters are...

MANUAL POSITION UPDATING: If a station knows where he is, he just zooms into his APRS map and moves the cursor to his location. Then he hits the INPUT-MY-POS command and enters his new course and speed. His posit will not only appear on everyone's screen, but he will also be deadreckoned along his course. Depending on the speeds involved and the size of the net, updates are only required when there is a significant change to course and speed. One station moving cross country reporting via HF set his course to 270 degrees and set in an average speed of about 50 MPH. Although he only updated his exact position once every few hours, because of the automatic APRS dead reckoning, his van appeared to everyone to move west giving a good approximation of his progress.

Although we used GPS equipped bicycles during the 1993 Severna Park marathon, we did not even bother in 1994. We simply monitored the voice nets, and occasionally whenever someone mentioned where the LEAD, TAIL or PACK runners were, the APRS operator simply updated the reported locations, and all APRS stations along the route could see visualy where these objects were, even without listening to the radio. Additionally, since the course is always known, and the speed of the runners in a marathon is very well known, the dead-reckoned movement of these symbols between updates was actually just as accurate as GPS! See MARATHON.HTM. A special version of APRS can actually deadreckon objects along a given course making all the turns indicated on the map. See DR.HTM.

MOBILE OPERATIONS: APRS was designed to make mobile operations with one finger relatively easy. The following summarizes the commands that are frequently used in the Mobile environment:

On any screen other than the MAP, this command will redraw the map centered on your vehicle. If you are already on the map, then GOTO puts the cursor on your station so that a single press of the PgUP/DN keys will allow you to zoom or home the map in one step.
Select this on the P-list. As a tracked station approaches the edge of any map, APRS will automatically re-draw the map in that direction. If TRACK mode is on, then the GOTO command will go to the Tracked vehicle.
Also activated on the P-list, will trigger BEEPs and cause your screen to be centered on the station if it moves. I use this one in my shack to alert me when the wife is coming home and I need to go to the kitchen and look busy and domestic on her return.
Use to manually update your position, or change your symbol, course, speed or comments.
Unless your exact location between point A and B is important, simply enter your estimated average speed, and the straight line course to B. This way, other stations will be able to see your dead-reckoned progress toward B and you will not have to make frequent updates. Since APRS also DR's your progress on your own screen, you will see the same thing that everyone else sees. You can tell whether you need to update your progress or not. You will notice, that on your own screen, each DR'ed position is posted at the same time that a position report is transmitted by your station. That is why the reports will be close together initially and be spaced further and further appart. In order for this DR to work on your own screen, you must not be in HSP or SPM modes. See the ALT-SETUP-GPS-OFFgps command below. If you want to see where your DR'ed position is at any time between transmis- sions, simply hit the space bar, and a fresh DR will be displayed.

CHEAP AND PLENTIFUL 8086 LAPTOPS: I prefer my old 8086 laptop monochrome LCD since it works BEST in bright sun! It only has dual flopies, but a minimum APRS system PLUS DOS will fit on a single 720K floppy. TO give you some more maps, though, you might want to use the DOS APPEND command to tell DOS to use the B drive as an extension of your A drive. To do this put your maps into a MAPS directory on B and use these DOS commands:

                           APPEND /e
                           APPEND b:maps /x:on
to cancel this later use   APPEND ;


See the GPS.HTM file for information on interfacing your PC to GPS or LORAN. There are several methods of interfacing depending on whether you have a dual or single port laptop, and whether your GPS/LORAN has a periodicity that is user programmable. Some useful commands are:

Synchronizes your PC clock to the GPS time in the next GPS posit heard. This is important to avoid dead- reckoning errors on small area maps! NOTE that this command only synchronizes the minutes, so you at least have to be in the right hour....
Sets both your own screen updates and the on-air transmission rates through the TNC.
Turns off the HSP/SPM modes without having to re-configure. This is useful if you are normally configured for HSP or SPM modes but are going to be doing manual updating. If the PC is left in HSP or SPM modes, then your local screen will NOT be updated on each DR. IF HSP and SPM are off, then each time your position is transmitted, a new DR plot is drawn.
Permits you to either communicate with your GPS if it has a bi-directional port, or to monitor the TNC. This command also switches the APRS port-splitter circuit in HSP mode so that you could monitor the GPS.
This key is called the QRT function because it forces your speed to zero as you approach your destination so that your posits will not continue to dead reckon on everyone's screens after you turn your system off.

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Mail comments/corrections on content to Bob Bruninga and on HTML formatting to Steve Dimse