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

[Matti Aarnio]

On Mon, Nov 19, 2012 at 09:03:35PM -0500, Robert Bruninga 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.

Reading the Speleonics Newsletter it is very clear that VHF works poorly.
High UHF may work (1.3 GHz), and low HF works (80m.)

Damp/wet walls of a cave are very much analog to waveguides at VHF and above
forming very effective low-pass attenuator. Low enough frequency of HF leaks
easier through, and penetrates rocks.

The TH-D72 works also at 70cm band.
With a proper antenna that would be better than 2m band.

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

There are 3d datasets and maps available for a price for those caves.

> Bob, WB4APR

73 de Matti, OH2MQK