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
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|