On Tue, 17 Aug 2004 06:31:48 GMT, "John" wrote:

Is there a PRACTICAL way of measuring the the improved efficiency that a
radial system brings to a ground mounted quarter wave vertical antenna?

I was wondering how my 30 radials over clay soil improve antenna efficiency.
Are there any easy measurments that I can do?

Hi John,

There are claims and there are measurements (and there is even
software to make the claims for you). Stick with measurements.

If your vertical antenna qualifies as a thin wire radiator, it will
exhibit, at resonance, a certain resistive component - let's call it
37 Ohms (caveat: this varies with wire/tube size which in turn
impacts exactly how tall, how resistive, and how much Q the radiator
has at resonance).

The trick is to be able to measure this resistive component within an
Ohm or two (or five). You may be able to infer it through the use of
a SWR meter if no other methods are available, and this method may
provide enough data to move on.

If you measure that same 37 Ohms, guess what? you've done your best
and no more radials are required. However, chances are you will read
slightly more than 37 Ohms (or whatever the starting figure is for
your style of antenna - style meaning a thick or thin radiator).

If you measure in the vicinity of 50 Ohms, you can be sure that you
have an additional resistive component that is combining with the
radiation resistance - two resistors in series. One of those in
combination is that same 37 Ohms (with the usual caveat of style) and
the other is the loss of ground, or the loss of poor fittings (tighten
connections). This may be improved through the addition of more
radials.

However, in the pursuit of nirvana (or simply wanting to dress like
you've obtained nirvana), be advised that few, if any, will notice
your "improvement" whatever you do.

Another caution, you may even be tricked by the loss of the cable
going to the antenna. This loss subdues the actual SWR at the
radiator and presents a more modest reading at the transmitter. In
other words, an antenna exhibiting the classic 37 Ohms may appear to
be a faithful 50 Ohm match through the loss of transmission line.

So, what kind of data do you have to offer? Also describe how you
performed the measurement and how remote the antenna is from where you
made the measurement. Also, give a description of the area
surrounding the antenna. Like, is it in the forest? Is it slapped up
next to your house that has a metal roof? You know, interesting
details like that which perturb the purity of science with the world's
reality.

73's
Richard Clark, KB7QHC

Hi

Is there a PRACTICAL way of measuring the the improved efficiency that a
radial system brings to a ground mounted quarter wave vertical antenna?

I was wondering how my 30 radials over clay soil improve antenna efficiency.
Are there any easy measurments that I can do?


Thanks

John
G4IRN.