[Lowfer] Alien e-probes

[Steve Dove]

Hi Bill,

Well, I was beginning to think I quite fancied Laurence's gig what with all the flash hotels 
and such, until the copper sheathing showed up.  Anyway, despite knowing better than 
to rise to the bait . . . .  Coming up with hard numbers would involve making up some 
arbitrary assumptions about the whip, input impedance of the sense amplifier etc. 

The short answer is not much difference between any of the three conditions.

A longer answer, third case first:  The mondo-hotel of the third condition is big enough to 
start to acting like a ground plane, so the only conditions affecting sensitivity are the 
basic ones of whip reactance vs. amplifier input impedance;  no return line impedances to 
take into account.

The first two cases are a straightforward choice between the return current finding 
ground via a skinny conductor (coax outer) or a fat one (building steel).  The antenna 
sensitivity is largely defined by the very high reactance of the electrically very short whip 
vs. the amplifier input impedance;  the ground return in this circumstance cannot help but 
be comparitively lower impedance, and won't affect this much.  That said, 1000 feet is a 
noteworthy proportion of the wavelength (1/7-ish), so whichever return is going to show 
some non-negligible impedance, with the skinnier wire likely a bit more reactive than the 
fatter one, so there may be a (probably very) minor sensitivity variation between them and 
a small affect on gain overall, though probably just fractional-dB-ish.   (At higher 
frequencies, where the whip is far longer with respect to wavelength so lower in 
impedance, and with the feedline often measurable in wavelengths, this 'feeder/antenna' 
gain effect is quite demonstrable, as described the other night.) 

So all three would behave similarly, like antennas 1000' up, and  I want one.

You know, I might just toddle off and model this, unless some other sicko already has.

        Cheers,

                Steve