On Mar 23, 2005, at 7:40 PM, K8fu@aol.com wrote:
> I think I got to verbose in trying to express the swr. With the
> antenna 22'
> in the air the swr on 10 and 15 were perfect (antenna tuned for the
> lower end
> of the cw band) but the swr for 30 was 3 to 1.
> With the ant on saw horses 3' above the ground the 10 and 15 meter
> readings
> remain the same but 20m now exhibits an absolute flat swr @ 13.800
> only 200kc
> below the targeted freq.
> What's up with this ????????????????????
3 feet is too close to the ground to get accurate measurements.
First, check all your measurements against the manual. The first time I
put together my A3S, I got the director about 6 inches short on each
side. Used it for 6 years without noticing.
Second, point the antenna skyward with the reflector 3-6 feet off the
ground. I did this by lashing a piece of mast to my deck rail, and
mounting the antenna on that.
Check the SWR curves. With the antenna pointing skyward, the
measurements you get should be about 50-100 kHz low - they will
naturally rise with the antenna on the tower. Note that super flat SWR
is also suspect - the antenna should have a response similar to the
manual.
If the curves don't look right, check your measurements again. If the
measurements are correct, one or more of the traps may not be working
correctly. These traps depend on a galvanized sheet metal screw for one
of their connections -- and it can often corrode over time. Tighten
these (you can access them by slipping the plastic end-caps off), or
replace them with stainless if they are badly corroded.
Insects can also bring debris into the traps. The traps can collect a
sizable amount of dirt and plant matter. Make sure the traps are clean.
You can often make this inspection with the end-caps off. If there is a
lot of debris, you may have to disassemble the traps to clean them.
Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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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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