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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