Here's a problem that's been puzzling me for a few weeks.
In the week between xmas and the new year (thanks to George, W1ZT for a
tremendous amount of help), my tower went up and the A3S with 40m extension
on top of it, but now I am experiencing some problem with the antenna that
I need advice for.
The problem is basically that the SWR on 20 & 40 is terrible, and it
fluctuates in an odd way. On 15, it is ok sometimes and off at others. On
10m there seems to be no problem. Here's a detailed description of what's
happening:
- I bought the A3S (w/ 40m) used. It had been up for a number of years, I
bought it from an estate, so it wasn't just "dumped" by someone.
- I cleaned it up as well as I could. Lots of bugs and stuff. Noaloxed all
connections. While on the ground (elevation 2ft), I checked SWR with an MFJ
259B and found that one of the 15m traps in the driven element didn't work.
I cleaned out the entire cast of "a bug's life" - managed to do that
without breaking the trap - and the problem was solved. I swapped the
director and reflector elements into the driven element position to see
whether each element has distinct resonances, and whether any other traps
needed attention. Everything seemed fine.
- The antenna was on the lawn chairs for a while, got rained on, and
remained ok in terms of SWR.
- Once the antenna was up on the tower (about 43'), I checked SWR and 2:1
bandwidth with the MFJ 259B. Some bands were a bit lower in frequency than
I wanted, but all were ok otherwise. Bandwidth was as specified / expected
and there were distinct optimum SWR spots. Hooked the antenna up to the rig
and checked again. Everything was fine on the rig's meter and on the
cross-needle SWR meter.
- Next day it poured. Really bad wind and rain. Now the SWR on 40 and 20
was shot. 2.5:1 or 3:1 at best. 15 got worse (2:1) and 10m was just fine.
Yes, the drain holes do face downward. All of them.
- Then it got freezing cold. The SWR got a bit better on 40 and 20 (not
great) and 15 looked just as it should. 10m no problem. Now when I transmit
on 20 and 40, the SWR moves up rather quickly. Within 10 or 15 seconds it
goes from 2:1 so far up that I can't read it anymore (>5:1 ?). Actually on
40m, depending on what frequency I choose, the SWR gets a bit better at
first, the races up. On 15m I can observe the same effect, but it is
miniscule (from1:1 to 1.3:1 or so). After a few minutes off, the SWR
recovers and I can repeat the test. If I reduce the power (max. 100W), the
SWR shift is slower.
- The antenna has been like this ever since (about four weeks now). When
it's warm, the SWR on 40/20/15 is consistently lousy. When it's freezing
(right now it is 16 degrees F), this odd drifting occurs on 40 and 20and
the SWR on 15 basically seems fine.
- For the sake of completeness, at first the driven element hung somewhat
at an angle, maybe 5 to 10 degrees, so water may have collected at the end
of the traps if the wind drove the rain in from the bottom. Happened while
hauling it up. But we straightened that out after about a week, and now
everthing is nice and straight - doesn't seem to have an impact.
I'm puzzled. We had some dry, above-freezing days (not many but a few), and
I was hoping that they might take care of the problem at least temporarily,
but no such luck. By the way, I'm using 100' of RG213. There is a Cushcraft
LAC-4H lightning arrestor where the coax leaves the tower (coax-sealed
connections, box sealed watertight). There is also a 9-1/2 turn, 4"
diameter choke balun right at the feedpoint of the antenna (Cushcraft
recommends 8 turns for the A3S, I added a another turn or so for 40m
operation). The balun sits on top of the boom, securely fastened to the
boom and truss pole, so there is little to no chance that water can enter
the coax at this point since it would have to penetrate the heavy
weatherproofing I put on and then flow upwards.
Another piece of information: I checked directionality and gain with a few
DX stations, and there doesn't seem to be a problem is this regard. I
worked ZL9CI (furthest away station for me) several times on both 20m and
on 15m - the antenna definitely showed directionality and, when compared to
my R-7000 vertical, gain. I just use the tuner to drive the antenna.
Has anyone seen this kind of strange behavior before? I'd like to have some
idea what to look for before I recruit help to get the antenna down and
start tinkering with it. Maybe the best idea is to just buy a new A3S and
bring the used one to a fleamarket - clearly an option if I put a price on
aggravation.
Thanks de Michael, K1JE
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