I wonder.....Is there is a simple way to compare the field strength of an
FCP with my current NON dense and uniform ground system, and draw
reasonably accurate conclusions about efficiency improvements >>>
Sure. You can probably determine ground wave changes in a vertically
polarized radiator with a simple test, if you wanted to do the work. Since
you wouldn't know the baseline performance all you really could say is if
it is better or worse than what you had.
Which brings me back to my general statement that a large change isn't so
much about how perfect new systems are, as how bad our old systems were.
:-)
I can tell you from direct experience at my house that near field effects
on 160 meters were noticeable at 300 feet, were barely noticeable at 600
feet, and were not measureable at 1500 feet. This was with an instrument
that resolves 100th's of a dB, and is accurate in tenths over the signal
level range. This is based on data acquired while attempting to null my
transmitter out of receive antennas, (bottom of page at
http://www.w8ji.com/antenna_coupling.htm) but would apply to pattern
measurements.
This effect was with a large directional transmitting array, so it would
be reasonable to expect a smaller array to require less distance. Based on
measurements, 500 feet distance should be pretty safe.
It does not require absolute field intensity measurements if you only want
to look at change. I primarily use two <$100 instruments here for playing.
One is a Sierra 303B portable level meter, and the other less portable
unit is an HP3586C.
I built small loop antennas for the 303B and calibrated them against a
rental FSM.
I have also used fixed wire antennas that I installed out in the woods
when I did not need an absolute level.
Having a portable selective level meter is worth it's weight in gold if
you do antenna work. I use the HP3586C to look at signal levels here in
the house. This lets me check gain and F/R of various antennas. It is far
more accurate than spectrum analyzers and S meters. The HP will do
averages, so it is great for testing transmitting antennas while listening
to distant signals on them, like using W1AW to compare two transmitting
antennas on skywave. I think I paid around $50 on eBay for it.
73 Tom
I'll have to agree about the HP-3586. I use mine as far as 750' back from
the house since I already have 240V almost halfway back and then run a long
extension cord.
It rides in a cart behind the lawn tractor after clearcutting a path to the
stone wall.
Carl
KM1H
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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