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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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