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

Les W6VN w6vn at 2pi.org
Tue Nov 20 01:10:25 EST 2012

A few hundred feet?  Really?  One reference I found measured about 0.7 dB/foot attenuation in limestone at 1.65 MHz. At 300' you're into moonbounce-like path loss on 80m, which isn't going to work with FT-817s using FM. Shorter distances might work -- how deep are the tunnels?

 -Les W6VN

On Nov 19, 2012, at 6:03 PM, Robert Bruninga <bruninga at usna.edu> wrote:
> 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 connection.
> Bob, WB4APR
>> 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 a
>> LAT/LONG grid on the sides so one can pinpoint one's position into the HT
>> 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 we
>> 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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