Topband: Inverted L observations and question.

[Tom Rauch]

>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