Bill,
If you switch the NE phasing line with the SW phasing line at the Comtek
box, does the high SWR stay with the NE position or does it move to the SW
element? If so, then I would suspect something wrong inside the Comtek box.
If not, then I would suspect it is external to the box.
Either possibility would be puzzling. I don't have a schematic of the Comtek
box, but looking at the diagram of the Collins box in ON4UN's book it's hard
to see any way that a bad part would cause high SWR on the main feedline in
one position but not the others. I would think that even a bad relay on the
NE element would just cause high reflected power to be dumped into the dummy
load. Same goes for a bad phasing line, coil or element. Seems to me that
you would see flat SWR at the main feed and high dumped power.
So, is it possible that the reconfiguration could have set up a situation in
which the NE element is coupling RF into the main feedline somehow? Are
there any new structures around that could be coupling to that element and
inducing RF into the main feedline (e.g., the tower with the new 40M beam)?
I'm kinda suspicious about that SW element because it just happens to be the
one that's 180 degrees out of phase with the NE element when the latter is
selected. Given all the measurements, it sure seems likely that something is
going on with the SW phasing line to be detuning the SW element like that.
Long shot: maybe the detuning is causing the pattern to get screwed up in
such a way as to induce strong RF into the feedline? (If that's happening,
the problem would actually shift to the SW element when you switch the
phasing lines at the Comtek box, invalidating the conclusion in the first
paragraph of this message.) You might get a clue by doing some receive tests
to see if the pattern in all four positions is working as well as it did
before you made the changes.
Could you provide more details on the installation? How many radials do you
have and are they elevated or on the ground? I'm no expert, but your dumped
power figures sure look a lot better than I've been led to believe are
normal for 4-squares (unless you measured at 100W instead of the 1000W
indicated on your web page.) I thought 5% dumped power was supposed to be
pretty good, but you're way under that -- even at the high end of the band.
Makes me wonder why you would even need the coils for switching between CW
and phone. Also, the impedance figures seem a bit high. I would have
expected to see them in the 25-35 ohm range with a sufficient radial system.
Please let us know what you discover. I'm within a week or two of finishing
off my 40M 4-square (the 240 radials are down, mounts are set, and 2 of 4
elements are built) and could use all the insight I can get.
73, Dick, WC1M
-----Original Message-----
From: Bill Fisher, W4AN <w4an@contesting.com>
To: towertalk@contesting.com <towertalk@contesting.com>
To: <towertalk@contesting.com>
Date: Sunday, May 03, 1998 5:52 PM
Subject: [TowerTalk] 4-Square Owners & Experts...
>
>I did some reconfiguration on my 80M 4-square this past month and after
>hooking it back up I noticed that I now have a high SWR on the bottom end
>of 80M in the NE position. Yes, high SWR to the Comtek box but only when
>the NE position is selected. All other positions have little to no SWR
>across the entire band. The NE position has 2:1 SWR at 3500Khz and 1:1 SWR
>at 4Mhz.
>
>I have checked everything out today. The relays in the box look fine. The
>measurements at the antennas look mostly OK. The dumped power in to the
>dummy load looks normal in all positions.
>
>I have summarized my investigation at
>http://www.contesting.com/w4an/newpage13.htm
>
>Any ideas would be appreciated. Also any comments on my readings would be
>appreciated.
>
>73
>
>Bill, W4AN
>
>
>Bill Fisher, W4AN (EX KM9P)
>http://www.contesting.com
>
>
>
>
>
>
>--
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