[aprssig] APRS in caves! (mammoth map) & HF test result

Robert Bruninga bruninga at usna.edu
Wed Nov 21 14:38:47 EST 2012

Initial HF Test Results:

Just to get some experience with HF on the ground, I connected two FT-817
portables with KPC3 TNC's to a pair of 80m dipoles and placed them about
0.4 miles apart on the ground (football fields less than 10 feet above
sealevel (sea was adjacent). See photo on http://aprs.org/cave-link.html .
Dipoles wrapped around the radio for carrying. The results were dismal.
Over that distance, signals were way too noisy for packet on 80m, even
after going back and getting a tuner. Lesson! Do not use magent wire, use
thick insulated wire for your dipoles so you can see them and so they
don't end up in a million knots!

Success: Before leaving, however, I shortened the dipoles for 15m and this
time, signals were strong and the link was solid.  Antennas laying flat on
the ground.  This test was not intended to test the through ground
performance, but was to test the node-to-node above-ground link
performance. This would allow these HF backbones to then link the below
ground packets back to headquarters without needing cross-band TNC's at
each node.

To do FM legally, we'd need to go to 10m and so the question is, how well
does 10m penetrate down to the cave?  There is lots of experience with CB,
so I guess I need to read up on it.


-----Original Message-----
From: Robert Bruninga [mailto:bruninga at usna.edu]
Sent: Monday, November 19, 2012 9:04 PM
To: TAPR APRS Mailing List
Cc: APRS at yahoogroups.com
Subject: APRS in caves! (mammoth map) & HF

HF VERTICAL LINKS:  I just realized that since HF penetrates a few
hundred feet vertically, we can use HF to link up to the surface every
7 hops or so.  Just an FT-817 with a DIPOLE above and below ground
hooked to a TNC can provide the link  Once above ground, then hops
continue on VHF.

Each vertical link takes up 2 hops, but it sure beats having to do 14.
 We need some people experimenting with HF packet FM (with squelch) on
80m (below ground since it would not be legal above ground)...  I
gotta do some research on HF links...

Also this gets more hams involved.  SOme hams not prone to caving, can
man the top side stations.  One of the HF links will be right in the
Lobby of the hotel and since it has WIFI, then that can be our IGATE!

> With this map, there's no easy way to separate the above-ground
> elevation contours from the cave tunnels.

Not sure I follow.  The tunnels are dark black.  Everything else is
color.  Its too early to start a huge investmnt in manually crossing
over the data to a vector file until I find out "which" path is the
MAIN CAVE.  The big portions are easy, but there are many places where
there are multiple thin lines.

> Also, is this just the first level of the cave, or is it
> several vertical levels drawn together?

all 6 levels.  So crossing black lines do not necessarily mean a


> Andrew Pavlin, KA2DDO
> ------Original Message------
> From: Robert Bruninga
> To: APRS at yahoogroups.com
> Cc: aprssig at tapr.org
> Sent: Nov 19, 2012 4:58 PM
> Subject: Re: [aprssig] [APRS] APRS in caves! (mammoth map)
> Mammoth cave underlay on local terrain map is now complete.  The map has
> LAT/LONG grid on the sides so one can pinpoint one's position into the
> underground to the same 0.01 Minute of LAT/LONG as on the surface.
> See http://aprs.org/cave-link.html
> So far, none of the modern clients seem to do GIF or JPG files.  But as
> get closer to the 2 March 2013 test, maybe someone can develop a vector
> overlay for the main passage.  Can YACC or APRSIS32 do APRS Overlays?
> Bob, WB4APR
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