[Lowfer] Alien e-probes

[Jay Rusgrove]

Peter

Check out the page below from from W8JI's website...about half way down he
shows an Eznec plot of a ten meter ground plane. Antenna lore would have us
believe that the four full size radials constitutes a "good" ground plane
when in fact it is rather poor.

Getting adequate feedline decoupling with an above ground mounted e probe
might be quite a challange. Would be fun to try Bill's 5000 X 5000 copper
top hotel with the e probe mounted in the center!

http://www.w8ji.com/common-mode_noise.htm

He's got lots of interesting stuff on his site as well.

Jay






Peter Barick wrote:

> 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
> ------------------------------------
>
> >>> 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
>
> _______________________________________________
> >From the Lowfer mailing list
> Send messages to: Lowfer@mailman.qth.net
> To sub/unsub visit: http://mailman.qth.net/mailman/listinfo/lowfer