[UK-CONTEST] A3S

[Colin Wilson]

Steve
Yes unfortunately I have experienced the same thing running 400w to the A3S 
pre MFJ days just after midnight in the middle of the IOTA on the island of 
Aran. The rain was lashing down and we had a force 5 to deal with in our 
faces which after a few hours the whole team was soaked to the skin and 
frozen! The problem was indeed a trap which had gone. This was a club 
antenna and I am not sure what happened to it but it lost us the IOTA 
contest that year! We did manage to get a VK2ABQ up in its place the 
following morning but it was no where near as effective as the A3S had been 
the day before. Later we replaced it with a new one post MFJ I would say.

Sorry not sure what help I can offer, do you have a choke/balun on the end 
of the line? Have you expeienced any lightening storms of late?  I have and 
it cost me my amp ATU, 30m dipole - PL259 melted!  Dito with my TH3 - 
suspect the balun went so replaced it and now okay.

Best 73 es GL your going to need it and rather you than me trying to climb 
the mast, at least mine tilts!
Colin CT7ACG/G3VCQ
www.glenridgealgarve.com



-----Original Message----- 
From: Steve Bunting
Sent: Wednesday, February 01, 2012 12:41 PM
To: uk-contest at contesting.com
Subject: [UK-CONTEST] A3S

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
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