Cave-Link can be established as Cave Rescue teams proceed into the cave by placing automatic relays called digipeaters at each major change in direction or weakness in signal strength. The map below shows 6 digipeaters labeled CAVE1 through CAVE6 in appropriate locations for communications in Collier's Cave near Florence, Alabama, my home town. The green lines are surface contour lines, blue is the Tennessee river and yellow is used for the underground passages. Red lines indicate overhead passages and violet lines show pits at lower levels. The dashed line is the trail above ground showing the path to the nearest road.

Notice the 0.125 eighth mile range scale of this map shown in the upper left corner of the map. Using the APRSdos software, you can zoom in or out for better resolution and scale. The next map is zoomed out to the 1/4 mile scale:

Zooming out shows where this cave activity is located in the area:

And continuing to the 16 mile range scale:

And finally at the 128 mile scale you can see we are in north Alabama.

COMMUNICATIONS: APRS works below ground just as it does above ground by links between small portable digipeaters as shown below.

Since APRS digipeaters relay digital information, voice communications is not possible. But positions, status and messages are. Typically, the cavers team will carry one of the Kenwood APRS data walkie-talkies shown below. A blow up of the screen shows that it displays to the caver the direction and distance to any object in his list. This photo is showing the UO14 satellite at 1483 miles, but could equally show the MOUTH southwest at 1483 feet. Ignore the grid-square in the middle of the display. It is not used for caving.

Similarly the screen can show text messages up to 48 bytes long displayed as two pages of two lines per page.

POSITION REPORTING: Of course GPS does not work underground, but any two people looking at the same map can report their position by simple grid marks on the map. The resolution and accuracy is as good as the map was drawn and the precision of the person estimating his coordinates on the map. As long as the cavers have a paper copy of the PC display map with a grid overlayed, he just manually enters his lat/long by looking at the grid on his paper map! For exxample, this version of the map has the grid overlayed. Team1 is located at N34 45.93 and W87 45.35.

MAP DRAWING: All of the cave maps above were drawn in only about an hour using the MAPFIX.EXE program provided with APRSdos. Remember, since GPS is not used inside the cave, the map can be any free-hand sketch that visually represents the best known knowledge of the cave. As long as everyone then uses this same map, then everyone will see the same tactical situation independent of the absolute GPS coordinates. This includes objects and notes placed anywhere on the map by anyone above or below ground.

MAP RESOLUTION: Typically in cave rescue, the real advantage of APRS Cave-Link is the digital text messaging of status and progress. Exact map tracing is only of value to show approximate positions. But if higher resolution than 60 feet is needed and if someone takes the time to sketch the map to that detail, then the sketch can be made 10 times larger than actual to give resolution down to the nearest 6 feet for example if such precision is available.

Not legal except underground or with Amateur Radio License.

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