[TowerTalk] A3S 20 Meter troubles

[Bill Coleman]

On May 31, 2004, at 3:48 PM, jtuel at everestkc.net wrote:

> I just put up an A3S on top of my new 40 ft tower.  It is a used A3S 
> and it was reported to work well prior to me getting it last fall.
>
> When I test it against my G5RV, the G5RV is a little better on 20 
> meters... The tribander is excelent on 15...
>
> I have good directivity, good nulls when I rotate it, but the SWR is 
> high and again, the G5RV transmits and receives better.

> From what I understand, the antenna does not have 20m traps to fail or 
> get clogged...
>
> I verified the element spacing and lentgths are correct, but the 
> antenna is not good on 20m...

Double-check the element spacing according to the manual, particularly 
the driven element.

Plot an SWR curve for the antenna on 20m. If it doesn't look like that 
printed in the manual, then something is wrong, likely with the 15m 
(outboard) traps on the driven element. The reflector and director have 
less effect on the SWR curve.

You may have to rebuild the traps. One suspect is the connection of the 
trap ends to the antenna elements, which is generally made with a 
galvanized screw. This connection can loosen over time, or it may 
corrode, particularly if moisure is allowed to collect in the trap. If 
either if these connections were bad, it might work OK on 10m/15m, but 
not at all on 20m.

A lot of times, insects can get into the drain holes of these traps and 
fill them with all kinds of debris. On a used antenna, it is a good 
idea to open up the traps and inspect them. You can do a pretty good 
job by pulling the plastic end caps off and blowing them out with 
compressed air. I've had my A3S about 15 years, and had to do this when 
I re-installed it after a move three years ago.

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901