[UK-CONTEST] A3S

[Steve Bunting]

Guys,

The recent co-ax chat has reminded me of a problem that I have with a 
Cushcraft A3S (at www.gb2gp.org.uk) and I wonder if I can tap into the 
expertise on the list.

The antenna was being used with 400W CW on 20m when the SWR shot up from 
1.4:1 to over 10:1 whilst transmitting. I swept the antenna with a 
miniVNA and it is u/s on 10,15 and 20m. The antenna is fed with 60m of 
LDF5-50 and ecoflex 10 around the rotator to the co-ax choke. I use 
N-types or 7/16 connectors throughout so don’t really expect there to 
have been any failure there and have tested at the bottom of the tower 
to rule out a co-ax fault where possible. My hypothesis is that a trap 
has failed in the driven element. Does anyone know if this is common 
with pre-MFJ A3S’s? Apart from a failed connector at the feed point, the 
traps are the only thing that can break – aren’t they? Perhaps someone 
here has experience with this antenna they can share with me off list.

In theory this is simple to solve, but the antenna is on top of a 30m 
tall fixed tower so trips to the top need good planning and any 
substantial mechanical work needs a posse assembling. I am trying to be 
as informed as I can be before embarking on tower top troubleshooting 
and hopefully a repair.

73
Steve
M0BPQ