[time-nuts] Timing on Ethernet

[Bob Paddock]

On Saturday 04 August 2007 23:54, Thomas A. Frank wrote:

> Ah, but what if one used the tunnel itself as a waveguide, and 
> propagated an RF signal down it? 

For many years I designed Coal Mining Equipment, I can
tell you from real world experience that it does not work that
way.  

We found the best "waveguide" experience was in
the range of 300 to 420 MHz, but the distance is very limited,
hundreds of feet at most.  The main problem at different frequencies
is the material becomes absorptive at lower frequencies,
or reflective at higher frequencies causing to much mutilpath
distortion.

Look at my site http://www.wearablesmartsensors.com/
under the 'Challenge' section and the blog there for some related
information.

You can find the results of some of the past real world underground
tests here:

http://www.msha.gov/techsupp/mcelroyminetestreport.pdf

"The Mine Safety and Health Administration formed a committee to evaluate 
communication and tracking system technology that could be adapted for
use in underground mines."

NIOSH has a test Mine near Pittsburgh if your inclined to test something.

We've just started to look into some old/obscure/esoteric
ways of transmitting signals underground.  Which we hope
will solve this problem, if we can overcome some funding and time issues.


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