If you have decent soil, 32 radials of the length you specified, will be
quite adequate and adding the number indicated by your friend is just a
waste of effort and money. Here's a relatively simple (if not completely
foolproof) way to tell if you have enough radials:
If you know the theoretical radiation resistance of your vertical over a
perfect ground: measure your current input impedance (at the antenna
feedpoint) with your current number of radials.
You can find the theoretical radiation resistance of your antenna by looking
up short monopoles in the ARRL Antenna handbook...Let's say on 40m, your HF6
is 28 ohms (it's shorter than a full 1/4 wave, so it will be somewhat lower
than the 37 ohms of a perfect quarter wave vertical) The shorter the
radiator, the lower the radiations resistance and you can read it directly
from a graph in the book noted above (or in Devoldre's Low Band
DX'ing...can't recall which) (or you can get it from using one of Reg
Edwards programs). Anywho, let's say it's 37 ohms.
Now you measure the input Z of your configuration. Let's say it measures 39
ohms. Your efficiency is 28/39 or 72%. If it were to measure 35 ohms, your
efficiency would be 80%. You can convert this all to dB loss and you will be
able to see if your current 32 radials are enough to make you happy. I found
26 radials that were 60' long were enough to give me better than 80%
efficiency (actually that number started to happen between 12 and 16
radials, but my soil conditions are very good).
This way, you take most of the theory and speculation out of things. Use an
MFJ-269 or some-such and you can do all the measurements yourself. I'm
betting you will find your efficiency better than 70%...also keep in mind
you have some additional losses from your vertical being a multi-bander, so
the efficiency I'm referring to is based on a single band vertical with no
additional loading/trapping/stubbing losses.
In short:
1. Find out what the Radiation Resistance of your shortened antenna should
be.
2. Measure the input Z at the antenna of your actual antenna/radial field
is.
Divide 1 by 2, convert to percent....a "rule of thumb" measure of efficiency
of your system has been obtained.
If you radial field were perfectly lossless, 1 would equal 2. Every ohm
above the theoretical radiation resistance of your antenna that you measure
is "loss" .
Have fun.
....hasan, N0AN
"John, N9JG" wrote in message
news:y1SBf.755914$xm3.21213@attbi_s21...
My antenna is a Butternut HF6V vertical. This antenna is ground mounted
and has 32 radials, which have been laid on top of the grass. The average
length of the radials is about 30 feet. I operate primarily on 40 meters,
and I seem to receive good signal reports.
Today, I ran into another operator on 40 meters, who told me that I would
get a large signal improvement if I increased the number of radials from
the current 32 to 100 or 120. In fact he said he had seen information on
the SteppIR website (http://www.steppir.com/) that supported his
assertion. Remembering how hard I had worked to install my existing 32
radials, I responded that the effect of quadrupling my radial count would
probably give only a small increase in gain of less than one dB. Indeed
Cebik's website (http://www.cebik.com/gp/gr.html) seems to support this
view with a graphic titled "Radial Length vs. Number of Radials". If I am
interpreting this graphic correctly, the gain increase from 32 radials to
128 radials is about 0.5 dB.
Any comments would be gratefully received.
John, N9JG