I've never been much of an advocate for just putting something up and
trying to qualitatively decide if it works well enough. It's a sloppy
approach and subject to all sorts of variables we can't easily
quantify. But that changes significantly if there is a reference
antenna to compare to that's far enough away to not complicate matters
with mutual interaction, for at least you have some indication of
relative performance. In this case, that's probably exactly what I
would do.
I also agree with the approach of not getting too particular about the
radials because they are almost certainly going to be affected by
proximity to the fence anyway ... 7 feet separation is definitely close
enough to be problematic. So I would just put up some counterpoise
wires and use a matching network somewhere in the feedline ... either a
network at the feedpoint or a tuner in the shack ... to sort out the
difference. For many years at my old Scottsdale QTH I used verticals
essentially cut to length fed against a counterpoise of a rats nest of
random length wires strung across the flat roof of the house. If you
use an array of radials cut to different lengths for each band that's
what you're going to essentially have anyway ... as modeling will
usually point out if you look at the impedances and current
distributions. I think you will drive yourself crazy trying to make
multiple radials resonant on multiple bands by trial and error.
And no, I don't think modeling is going to be accurate enough to handle
multiple radials close to ground in the proximity of a chain link
fence. I'm a firm believer in using a tuner when one is called for.
73,
Dave AB7E
On 10/2/2019 9:41 AM, Mark - N5OT wrote:
Hi Ed,
Do I understand correctly that you have two antennas and you are
asking about making changes to one of them? If the other antenna does
not change, then you could compare the new unusual design to the other
design that has not changed, and you would know the answer. If it was
me, I might be inclined to "put it up and see what happens" but be
advised that this approach is slovenly and without merit to some,
which could open you to disparaging public comment, regardless of how
loud your signal becomes because of the new antenna.
For the humor impaired, that was a little bit of a joke really.
Actually if it was me, given that you only need two resonant radials
to make a complete system when they are above ground, and from what I
understand this works when the two radials are symmetric about the
feedpoint, I would not be able to stop myself from digging out some
ribbon cable and cutting it so that I had one wire in the ribbon cable
per band per side that was the right length. then I would have
everything I need in a single assembly with a single attachment point
at each end, per each side of the feedpoint.
Then, I would mount it so that the radials were also symmetric about
the fence.
Some wax poetic about tuning the radials for resonance, but I, being
confident the system was symmetric, would not look back at that, I
would cut the radials to approximate a resonant dipole, feed the whole
thing with a matching network located for my personal convenience, I
would make the radio happy with a swell SWR, and get on the air and
work other radio operators. Comparing it to the other antenna could
yield confidence or concern, a not-inappropriate currency in my way of
looking at it.
Bear in mind, it's possible the exact ribbon cable one uses might turn
out to be too small. This is easily determined without math as
follows: Put it up. Use it. If the ribbon cable heats up, it is too
small. If the ribbon cable does not heat up, it is not too small.
Flames could be an indication too. Watch the SWR while doing the
experiment.
You might be able to do it differently than I have described and
achieve what some would call "better" results, which would be an
arguable statement, and then the argument about the results and how to
measure them (seasoned with comments about engineering practices),
would occupy the posts of this email reflector in the grand style to
which we have become accustomed.
Or, you could do what I have described and get on the air and enjoy
radio contacts from your warm cozy shack during the cold winter that
will soon be upon us.
And thanks for getting me thinking. I might have to go outside and
try that.
73 - Mark N5OT
On 10/1/2019 9:52 PM, ed_richardson@shaw.ca wrote:
Getting ready for another contesting season from my Postage stamp
size City Lot. In previous years I have installed a winter antenna
(Steppir Vertical) in the rear yard as a second antenna to the tower
mounted beams. In the past I have had had so-so success laying out
50-60 radials around the base of the antenna.. The problem is there
is a lot of ground clutter such as trees and wooden fence in close
proximity to the antenna.
I was considering mounting the antenna about 13-15 above the ground
and above a 7 foot high chain link fence. I was then planning on
using 2-3 resonant radials on each band (40/30/20/15 forget about 10m).
Has anyone had any experience with a similar configuration? Obviously
keeping the radials away from the fence would be important.
Thanks for the bandwidth!
Ed VE4VT
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