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Re: LF: Dreamers

To: <[email protected]>
Subject: Re: LF: Dreamers
From: "Graham" <[email protected]>
Date: Sun, 2 Oct 2011 23:59:23 +0100
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Top band  dipole  is  ~~  1 meter  , anyone  tried using  one  in the  local  pond  ?
 
Sonar target  resolution  and  towed  arrays next  ? , dose  say  the  LF  group !
 
G..
 
 
f = 8.97 kHz
lambda in a medium: 14.9 meters
 
f =  82 Hz ( ZEVS)
lambda in a medium: 156 meters



Sent: Sunday, October 02, 2011 11:27 PM
Subject: Re: LF: Dreamers

W dniu 2011-10-02 17:48, mal hamilton pisze:
IE
Dreamers, alias snails es crocodiles. I suppose they do have something in common, especially the operator who works mostly underground following gas pipes and water pipes, and then gets confused at roundabouts
Keep smiling !! and come up for air except you are nuclear propelled
 
g3kev


Hello Roger, LF/VLF "Dreamers" ..

i will also make a reference to your " underground work" though it will be slightly different  from Mal observations....

Very often the medium over which the  radio wave propagates ( soil, sea water) is regarded as a semiconducting uniform medium characterized by
 its dielectric permittivity and conductivity - for such a model rather basic physics of dielectrics can be adopted.
Therefore, we can use the concept of a complex dielectric permittivity which results in a few simple eqns. from that equations
 we get some numbers which i would like to present here.
it is very likely that you already know those numbers/estimates but for me some of them came as a sort of surprise.....

Some introductory remarks: A wave propagating in a free space is attenuated in a medium and is strongly shortened. We can define so-called
"penetration depth" as a depth at wich the amplitude of radio-wave is e times smaller (2.718...) than the amplitude in a free space
( reciprocal of attenuation factor)
Also , [it was the most interesting  to me] , we can estimate ( connection with Leontowicz conditions, boundary continuity eqns. etc..) how many times the horizontal component
of a wave  electric field  in a medium  is greater than its vertical counterpart. At the same time this quantity shows how many times
 the vertical component of E field in a free space is greater than horizontal component of a free space E-field vector.
Finally the numbers..

for the sake of curiosity i took the salt water at first ( Mal was talking something about nuclear drive/subs) :)

eps(r) :81 and sigma ( conductivity of a salt water: 5 Siemens/m)
 of course, the sigma depends strongly of salinity  sigma = 5 is just a reasonable example

f = 136.172 kHz
lambda in a free space: 2201.6 meters
lambda in a medium: 3.81 meters
penetration depth: 0.61 meters
H/V ratio in a medium: 812.7


f = 8.97 kHz
lambda in a free space: 33421.7 meters
lambda in a medium: 14.9 meters
penetration depth: 2.376 meters
H/V ratio in a medium: 3166.5



f =  82 Hz ( ZEVS)
lambda in a free space: 3656 KILOmeters
lambda in a medium: 156 meters
penetration depth: 24.8 meters
H/V ratio in a medium: 33118.0

and now  the soil:

 i assumed epsilon(r) = 4
 sigma = 0.003 S/m  / it is supposed to be something between dry soil and slightly wet/moistured  or so.. /

f = 136.172 kHz
lambda in a free space: 2201.6 meters
lambda in a medium: 155.6 meters
penetration depth: 25.0 meters
H/V ratio in a medium: 19.9

f = 8.97 kHz
lambda in a free space: 33421.7 meters
lambda in a medium: 609.2 meters
penetration depth: 97.0 meters
H/V ratio in a medium: 77.6

         
                                                                  73, Piotr, sq7mpj

                      
 


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