>The bandwidth between the 2:1 SWR points is about 80khz
>with just the elevated radials connected. When I connect
>the on-the-ground -radials the bandwidth gets worse i.e it
>changes to about 100khz. This is opposite to what I
>expected. I thought the additional radials would lessen
>the ground losses but they seem to have increased the
>losses.
Hi Frank,
I know that's another one of the very popular myths about
antennas, but bandwidth is not a reliable direct indicator
of efficiency. The only time a bandwidth change indicates an
efficiency change is when loss resistance of the system is
the only thing changed.
If I have a 1/4 wave vertical using an elevated radial
system with one short radial resonated by a series
reactance, and I change ONLY the ground system to 60 quarter
wave radials laid on the ground, efficiency probably goes
from significantly less than 25 percent to nearly 100
percent. At the same time bandwidth will greatly increase.
The antenna gets wider while the efficiency improves.
If I have a mobile antenna with a small stinger above the
loading coil and I replace the stinger with a large hat and
retune the coil, bandwidth will go up and efficiency will go
up.
If I have a shunt fed tower with a very thin drop wire and
increase the size of the drop wire significantly efficiency
will increase while bandwidth will get much wider.
We really can't tell anything reliable about efficiency
change by measuring bandwidth change.
Of course I'm not saying your antenna improved or did not
improve, or that connecting the ground radials to the
elevated radials helped or hurt. It's pretty well known that
connecting any poor ground path to earth to a small elevated
system slightly decreases efficiency of elevated radials.
With less than a dozen elevated radials you should even
choke or isolate the feedline for common mode current. So
you may have made things either worse or better.
Radials on the ground probably aren't going to help much
unless you use enough of them (maybe 20-30), and when you do
there isn't really any reason to use elevated radials along
with them.
73 Tom
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