[aprssig] APRS, caves! & More HF

Les w6vn at 2pi.org
Thu Nov 22 01:55:55 EST 2012


Nice.  One thing, though: Your calculation seems to assume that all of 
the power at the target depth ends up in the receive antenna.  That's 
not going to happen.  But I suppose the good news :) is that the 
attenuation through the ground is so high that the additional loss due 
to the small size of the receive antenna probably only amounts to a 
change of a few skin depths.

   -Les W6VN

On 11/21/2012 10:18 PM, Steve Noskowicz wrote:
> I did some back of the envelope calculations...Well... Excel anyway.
> Looking at the Skin depth chart for 'earth' in the Speleonics 
> newsletter #1 gave me an idea.
> Calculate the path loss of earth on 160 meters using skin depths.
> Given that one skin depth has 8.7 dB of loss...
> And assuming you can get a full 5 watts power into the ground at the 
> Tx surface...
> And assuming you can get all the energy out of the ground at the 
> receive "end".
> Looking at the Skin depth chart for 'earth' in the Speleonics 
> newsletter #1...
> The middle curve of .01 mhos/meter of ground conductivity shows a skin 
> depth of about 4 meters at 2 MHz.
> With a receiver sensitivity of -110 dBm (0.7 uV) this is a path loss 
> capability of 147 dB.
> Which translates to 17 skin depth or 222 Feet.
> Using the "best" conductivity curve (0.001 mho/m) I get 888 feet.
> These must give a rough estimate of some sort of an upper limit for 
> through-earth radio ... in rough numbers, very rough, of course....
> There is also a lot of info on low freq Magnetic communications in 
> those newsletters.
> 73, Steve, K9DCI
>   Fun exercise.

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