[Lowfer] Alien e-probes

[Peter Barick]

Bill, others,

I was left wanting with Bill's resolution and implication of his
explanation, that only a very large area would suffice for a true GP. In
the real world, and certainly 1,000 ft hotels are part of that, a modest
100x100 ft top plane appears to be a substantially dimensioned element
to act as a (yes, imperfect) GP for the given probe of this discussion.
But is it adequate, Bill seems to say no and alludes that the natural
ground, 1,000 feet below, would usurp GP duty, thereby allowing the
feedline to remain "active" as an receptor and not as a proper feed line
from the roof mounted probe.

If that is true, then what does one make of the AMRAD's LF probe using
a smallish metal roof for GP and reported noise reduction and stated
effective reception? Are we hyping blackboard theory vs. the practical
here?

I'd like to place a similar LF probe at top of a 55 ft tower and over
the tree canopy. In doing so a GP would be made as part of the mounting
base, say 10 3-ft brazing rods in radial fashion. The down line,
carrying sig and dc, would be affixed to the tower until it departs for
the shack and would terminate in ferrite. Then to what degree would this
pass/fail Bill's analysis for effectiveness?

Peter
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>>> ashlockw@hotmail.com 09/14/03 12:18AM >>>
Hi Steve,

I agree with your analysis of the first (tall) hotel. The 100ft by
100ft 
profile is small compared to a wavelength and the true ground plane is

actually the ground; not any part of the hotel. There would be a large

increase in signal compared to the signal measured at ground level,
however, 
due to the 1000ft effective height of the antenna. Based on my
experiments 
this increase is approximately equal to the length of the antenna
(assume 1 
meter) divided into the total height above ground (~312 meters). I
believe 
this effect is due to probing the changing E-field at two locations 312

meters apart. The instantaneous voltage induced is proportional to this

distance as long as it is much less than a wavelength. I therefore
conclude 
that VO1NA's signal at ground level would be approx 100uv/321 = .32uv
and 
assuming a 1 meter antenna .32uv/m.

The second hotel has such a large profile that its structure would act
as 
the ground plane for the signal. I therefore believe that the .32uv/m 
E-field would produce a .32uv signal on the top floor.

Let me know what you think.

Bill A