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[aprssig] APRS, caves! & More HF

Steve Noskowicz noskosteve at yahoo.com
Thu Nov 22 06:50:12 UTC 2012


 
 
HA HA HA!  LOL for sure. ...  like! 

 But check this out ! !
 
  I emailed the Speleonics news letter editor some questions and after posting my calculations here, just got a reply that said, in part:
 
"... On the through the earth radio, yes, I have been doing it for quite a while and have some interesting experiments coming up at about 800 feet deep with WSPR.  I have had great success at depths up to 200 feet with WSPR and really like the exact SNR reporting (even if I don't agree with the basis for that SNR - I can hear the signal down to about -12 to -15 dB).

I have been having an exchange with Bob Bruninga about his experiment.  I don't know if I will be able to be there in March, but it would be fun! ..."
 
Cool juxtaposition of numbers, eh?

73, Steve, K9DCI USN (Vet) MOT (Ret) Ham (Yet)
 
--- On Thu, 11/22/12, Ray Wells <vk2tv at exemail.com.au> wrote:




This is becoming an Aladdin's Cave of (technical) treasures.

Sorry, I'm off my medication!!

Ray vk2tv

--- On 22/11/12 17:18, 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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