[TowerTalk] Isolating adjacent 4-Squares
no9e at arrl.net
Tue Dec 22 10:09:45 EST 2020
Actually, Charlie's problem is an exciting one to look at and experiment.
Not sure what he means that the array is not working. I suspect poor F/B or
high SWR. Many ways to troubleshoot when the weather is nice. Necessary
items are antenna analyzer and large snap-on toroids.
1. Is the impedance at resonance at each feed point same for all the
verticals and close to 40 Ohms?
a) if some impedances are widely different, check the hardware.
a) If the same but the impedance is not 35-45 Ohms, the coupling structure
is symmetrical to all the verticals (most likely the tower).
b) if impedances are not the same, the coupling is likely unsymmetrical.
Try to disconnect other antennas, put snap on toroids on various cables and
wires, and see whether it makes a large difference in impedances or SWR.
If it something does, you have a culprit.
2. Are impedances similar at the feedpoint?
If not, check the phasing lines.
3. Have a switch to listen to each vertical separately. If there any
a) If not, the tower is likely not in resonance.
b) If yes, the tower is likely in resonance, and the regular 4sq box would
not work well.
However, a custom box or just custom phasing lines could bring performance
above the regular 4 sq since the tower will be used as part of the antenna.
One way to check for it would be to use only two inline verticals and apply
a custom shift box a la W9AD unit:
I had trouble with my 80 4 sq. The problem was a feeder to an 80m dipole
off the top of the tower. I also tried a 2 el 160m array to top of 100 ft
trees with 4 elevated radials. But one such vertical was 8 db below the
100' shunt fed tower so the effort would not pay off. Combined effects of
tree proximity and elevated radials. In both cases the simulation would be
On Sun, Dec 20, 2020 at 12:24 PM Charles Morrison <junkcmp at gmail.com> wrote:
> I have an 80M wire 4-square around tower #1. (90ft with two big 10M & 15M
> monobanders) Each vertical has 12 above ground radials and is tuned to
> 3535. All guys are broken with insulators.
> This array works well.
> My second version of a 160M wire 4-square around tower #1 was raised last
> week. They are Inverted L's to a 120ft tower. It already has two Cushcraft
> 40-2CD's and a big homebrew 20M6L OWA yagi. All guys are broken with
> insulators. Each Inverted L has 20 on-ground radials and is tuned to 1725.
> The closest 80M element is 40 feet from a 160M element.
> The 160 is not working well. I will be testing the phasing lines once this
> snow melts. ###
> I want to apply a passive device to further isolate these systems. I'm
> thinking of a 1/4 wave 50 ohm shorted coaxial stub on each feedpoint. My
> first guess is the 160 elements.... ?
> Alternatives are to move one of the arrays.... but I'd rather explore
> making them work where they are.
> -Charlie N1RR
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> TowerTalk at contesting.com
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