Hi Don,
I hope you don't mind my pointing out something. While your
suggestions are all good ones, I can site cases where the rules are
broken.....
> Something to keep in back of your mind if you're shunt or series feeding
> your tower for 160. If your antenna has a wonderfully wide bandwidth,
> it may be due to a mediocre ground system.
Consider a case of a single (or small number of) elevated resonant
radial. Now the radial's bandwidth (it will be very narrow compared
to a tower) will actually decrease the bandwidth of the system
while reducing efficiency. If we add radials, bandwidth will increase
and yet efficiency increases!
If we shorten that resonant radial(s) and load it with an inductor, the
effect is bandwidth decreases while efficiency also decreases!
It's a good idea to not pay too much attention to bandwidth as a
sign of system efficiency unless you really have a feel for what it
should be with the system you have. My most efficient mobile
antenna also has the widest bandwidth, it's another "rule breaker"!
So how can we measure efficiency? We can't. All we can do is go
out some distance (it doesn't have to be a mile, a thousand foot or
less would be OK) and measure a reference signal in a clear area.
Don't move that antenna or touch that receiving system, and go
back and quickly add eight or ten temporary cheap thin wire radials
as long as you can reasonably make them. If the signals doesn't
change, you probably are OK.
My system starts to fall off noticeably at about 30 radials, so I use
60. My tall vertical has 100 radials, but only because the radials
are LONG (over 200 feet in some directions).
If you have a short vertical, or a close spaced phased array, ground
losses go up and you might need more radials. Don't just connect
and disconnect radials to see if they help, because just having
them there unconnected helps reduce loss to some extent.
73, Tom W8JI
w8ji@contesting.com
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