I strongly disagree with the person who said you should not worry about having
1/4 wave radials, and to go with less length radials; unless you were putting
out 120 radials!!
RADIALS DO WORK, ESPECIALLY IF THEY ARE CUT TO RESONANT QUARTER WAVE lengths.
Random lengths won't work as well, on given bands.
Especially, if you add at least one resonant radial, it will improve the
reception in the direction of the radial by a possible doubling of received
signal, and this is shown by my experiments some time ago above generally poor
RF ground, with elevated radials.
It follows then, that as a minimum, four radials, in the four compass
directions is a pretty good compromise for the ham who cannot put out 120.
(BTW, do you know why 120 has always been talked about?)
That is because that is what is done with AM broadcast stations, who do NOT
use resonant verticals, (Theirs are typically shorter than a quarter wave),
and therefore really need a good RF ground even more than Hams need it.
Actually the early work showed little difference above 60 radials or so, but
the experimenters, said, to be conservative, they would use 120, and it has
been done that way since. (Either Wheeler or RCA Labs did that in the 20's or
30's I think) Of course, 120, means each radial only has to support a 3 degree
sector of the azimuth of the vertical.
Think of it another way, the quarter wave vertical for a given band, and at
least one quarter wave radial, forms the basic resonant antenna, a HALF WAVE
dipole. Specifically, an "L" shaped dipole, but a dipole none the less.
It will perform best in the direction of the radial. Adding quarter wave
radials for other directions will even up the pattern of radiation. With four
radials, you will then have the fundamental Vertical Ground Plane Antenna.
This was the basic antenna used for years for single band DX stations, or VHF
Police radio systems. It works very well, especially if the antenna and its
radial system is elevated over the possibly RF lossy earth under it. Ground
mounting a vertical couples you to higher earth losses from the capacitance
between the earth and the antenna. That then requires more radials to
counteract the earth loss, by creating a conductive radial or ground screen.
There is a very interesting AM broadcast station North of the Plaza in Sante
Fe, NM. It's antenna system is built over a parking lot. The cars are
covered with a wire mesh, high enough to drive under. That is the ground
system of the antenna, and its tower then rises above the Netting. It would
be interesting to compare this station against one of similar power, but with
conventional ground laid radials, but I have not had the opportunity.
But back to the basic questions. Yes, you can leave the Romex electric cable
intact, cutting the various conductors to the three bands, quarter wave
lengths.
There may be some proximity effects of the capacitance to adjacent conductors,
which may change the quarter wave resonance from that predicted by the classic
formula, (234/MHz), but that could be tried out with one Romex piece before
you cut three more pieces of Romex cable.
In this case, the analogy is to parallel dipoles on a common feed point
insulator. They can be made to work, if you realize some interaction may
change the lengths for each band from classic dipole formula, (468/ MHz). In
either case, an Antenna Analyzer of the Autek or MFJ type is most useful.
If you did not want to use up too much of your roll of Romex, model the
parallel radials at say 6 and 2 M, which would only use 5 feet of Romex.
For this, of course you need the VHF versions of the Autek or MFJ analyzer, or
a grid dip oscillator.
Just such a scheme of parallel radials has been used with commercial
verticals, and the current commercial version that comes to mind is the
Butternut, which was reported to work very well (once tuned), by a ham
electronics engineer friend here at the research lab.
The effectiveness of the resonant radial, is the whole being of the Tiger
Tail, (tm) sold by Antennas West for use with two meter radios. It is simply
a resonant quarter wave clipped to the ground side of the HT antenna
connector. It then forms a vertical dipole, vastly superior to the rubber
ducky alone. It is even better, if you use a telescoping whip of 19 inches to
replace the ducky.
Hope that helps conceptualize what a radial or counterpoise does for you,
Stuart K5KVH
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