Topband: My Turn For a Brain Pick - Sanity Check
charlie-cunningham at nc.rr.com
Fri Jun 7 16:04:51 EDT 2013
I'm most suspicious regarding your radial systems:
* Are your radials resonant? For the purposes that you are attempting,
they need to be, in order to maintain the phase relationship between the
driven element and the parasite.
* Are your radials elevated?
* Do your radial systems overlap or pass close to each other?? You can
have considerable unintended and competing coupling via the radials that can
destroy the parasitic relationship between the driver and parasite.
I am attaching and EZNEC file of a 5-element 80m array that I designed and
built some years ago, for a friend, Jim, W4RS, when he was in Virginia. It
was a wonderful "kick-ass" "knock-'em-dead" antenna for tough long-haul
international DX paths and a real "pile-up buster"! If you have access to
EZNEC you can have a look. It consists of a central GP with 4 parasites
arranged around it in a square. Each of the parasites has a 6 ft shorted
line of 450 ohm ladder line at the base. The inductance of the 6 ft shorted
line tunes the parasite as a director. Then the shorted line can be shorted
an inch or so from the attach point at the vertical element and the radials,
to switch it to director tuning. The result is that in the diagonal
directions the array basically operates as vertical 3-element 1/2 yagi. In
the N/S/E/W directions it operates as two horizontally stacked 3-element 1/2
yagis that share a common driver.
If you have access to EZNEC. Please examine how I handled the resonant
radials. The central GP driver has 4 elevated resonant radials that extend
outward past the parasites. The parasites each have two resonant elevated
radials that are at right angles to one another and are led away from the
center of the array to minimize the radial coupling. The result was a
"killer" 80m DX array that was the envy of a few serious 80m DXer down here
in our area.
If you want to play the beam steering, go into the "Transmission Lines" menu
in EZNEC and switch them between 6 ft and 0.1 ft. You'll get the idea. The
beam can be steered around 8 points of the compass rose. The beamwidth is
wide enough to provide complete azimuth coverage at full gain. F/B is
As for 40m, I've never tried that with parasitic GPs. I have built several
vertical 40m yagis that employed vertical 1/2 wave elements that were
supported by trees or overhead lines for really tough "new ones" with huge
hungry pile-ups with excellent results in all cases. (Electromagnetics works
-even for us "poor folks"!)
The array that I've shared with you should be scalable to 40m. I've done
that with EZNEC, but never built it.
I don't have any real feel for parasitic arrays with buried radials, or
"radials on the ground". I expect that such arrays might require some tricky
BTW - in my experience, with elevated resonant radials, once we have 4 - we
seem to be reaching a "point of diminishing returns" and increasing the
number of resonant elevated radials doesn't seem to buy much!
Anyway, good luck! I would expect that a 2-element 40m parasitic array,
that has provision for switching the parasite between reflector and director
tuning could be made to play pretty well! If you are 5m from the array, I
would think that your measurements are pretty good except for elevation
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Jim GM
Sent: Friday, June 07, 2013 12:14 PM
Subject: Re: Topband: My Turn For a Brain Pick - Sanity Check
I think your too close to tell, or just coupling into every thing around
there. Knowing you I am sure you have done every thing right. Try calling
CQ during day light hours and see what signal strengths the Reverse beacons
give you. http://www.reversebeacon.net/main.php
Problem with doing this is the beacons may not re-spot you until your off
the air for say 15 minutes or shift frequency. I do not know how they
All good topband ops know how to put up a beverage at night.
More information about the Topband