I finally installed earlier this spring on a light aluma tower T-150 a
Cushcraft A3S triband beam I have owned and had up in several configurations
over the past 6 years. I measured all parameters prior to leaning the tower,
rotator and antenna into place. The SWR was acceptable on all three bands
10/15/20, with slightly higher SWR on 20 than I would have liked but tolerated
it and have made many nice contacts. The beam was showing forward gain and
nice front to back and front to side ratios, several S units, for example with
beam on the station they would show S9 and with the beam turning away the
station would go down to S3 or S4 which seemed reasonable to me.
After a long hot drought we have had steady hard rain for several days and it
is still overcast and damp outside. I had time this holiday weekend to look at
the SWR with an analyzer on 20 meters and got up on my roof and slightly
shorten ( by 1 inch per side) the outside most part of the driven element as it
has always been resonant on a lower frequency than where I normally operate. I
came back to the shack and now instead of a 2.5+ : 1 SWR it is 1.5 : 1 where I
operate. Checking 15 and 10 to my horror the SWR has risen to 3:1 on both. I
do not get a definite dip on either band as I have observed in the past with
the analyzer on 10 and 15 and now have a resonant point at 36 MHz of 1.2:1.
I did not check the SWR or analyze the antenna on 10 or 15 meters just prior to
the adjustment, only making measurements on 20 as it was the concern and I did
not think that adjusting 20 would have any effect on the other two bands. I
previously had a very nice dip on both 10 and 15 meters when I checked it a
couple of times in the past several months.
It is my presumption (correct?) that perhaps water has entered one or more of
the traps? But why would 20 meters still be good? I was thinking that if 10
or 15 were affected then 20 would definitely be thrown off as well.
The only access I have to the antenna (unless tower is lowered on its hinges)
is from the roof and that is limited to the outside parts of the elements as
the antenna is rotated over the pitch of the roof area. I do not feel
comfortable climbing the light weight tower, an aluma tower t-150 which nests
the antenna at 30 - 32 feet just above the upper section of the tower on its
mast mounted rotator which is just above the top shelf of the top section. The
antenna is mounted only 2' above the rotator but still more than 6' or so above
the top of the lowest section of the tower. If you are familiar with this
tower it is the smallest two sections aluma tower made that cranks to 50 feet
and each section is 25' long.
I have purchased a 12 volt positive braking in/out vehicle winch which is rated
for well over any weight this tower, rotator, antenna combo carries and am
considering mounting it on the side of the house about 12 foot up and using it
to be able to lower the tower, rotator, antenna combo and raise it again. The
base hinges are two pieces of aluminum brackets in bolts which go into the
concrete base which are around the lowest rung on the face away from the house.
A corner of the lower tower section is in an eve bracket at about the 16'
level, a face does not rest against the house only a corner which allowed us to
walk the tower, rotator, and antenna up with two people walking and one person
pulling on a rope attached through a heavy eye bolt in the side of the house.
Anyway, my plan is to wait a bit for warm, hot, dry weather again and recheck
to see if improvement occurs.
On an old A4S I refurbished a couple months ago I noted pot metal screws
securing the coil forms inside the aluminum trap covers, these screws had badly
corroded and were replaced by stainless ones I got at hardware to match the
originals. I am now wondering if I should have done this to the A3S as well
but it has always been flawless to date and I was in a hurry to play. Ha ha.
Any comments or suggestions, pointers etc. appreciated in advance.
Thank you.
Gene A Bigham KB0GU
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See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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