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[aprssig] APRS, caves! & More HF

Steve Noskowicz noskosteve at yahoo.com
Thu Nov 22 07:28:53 UTC 2012


 
> Steve,
> Nice.  One thing, though: Your calculation seems to assume 
> that all of the power at the target depth ends up in the receive
> antenna.  

Thanks, just some random musings and you can see from my last post that there is an interesting similarity in numbers between mine and the tests that Paul, the Speleonics Editor mentions.  A real hoot!

 No 'seems', there Lee.  I *do* state that I assume that.   I know it is a big assumption, but, hey, it's all just on an envelope after all.  (;-D)

Steve, K9DCI  
P.S. 36+ years in the field can give one just a bit of arrogance concerning ones assumptions.  I refer to it as a highly developed "gut feel". (;-)

Time will tell, eh?

Time for bed...




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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