Pro-57b

[n4si]

> Greetings all, 
> 
> I put up a Mosley Pro-57b about a year ago, and am experiencing a slowly
> climbing SWR on 10 & 15/17 meters.  At first it was fine except for a
> slightly high SWR on 10, 1:8:1. On 15/17 it was fine @ 1:2:1. 12 & 20
> meters are virtually flat @ 1:1:1.  (using 4 meters
> rig/tuner/amp/mfj-249 and averaging.)
> 
> Now it's slowly climbing on 10- it's over 2:5:1 which precludes my usage
> of the amp.  15 & 17 now seem to be following- From 1:2:1 up to 1:8:1
> now.  The factory told me to check the length of the coax/shield "Y" at
> the feedpoint and try making it shorter.  
> 
> Before going through the hassle of lowering the yagi and making the
> change, has anyone else experienced this sort of problem with the
> Pro-57b ??   If so what was your solution?
> 
> I love the antenna, 85 confirmed in 1996.  But this is beginning to be
> concern. 
> 
> Thanks, 
> 
> Dave - KB6JOX


Dave,

I installed a PRO 57 or 67 (I don't remember which) for a friend
several years ago. One thing I didn't like about it was how the
feedline attached to the tuning rods. We noticed anomalous SWR 
readings which weren't explainable any other way. The clamps were 
actually a slide fit on the rods.

Aluminum clamps aren't very good in that application due to their
malleability. So I redesigned the attachment using stainless steel
radiator hose clamps (I use lots of these in lots of applications
along with liberal amounts of conductive grease such as NoAlOx or
Penetrox), and crimp-on terminals. 

I formed the terminals to the radius of the tuning rods, clamped them 
into place with the hose clamps, and ran the numbers again; voila! 
Everything was right where the charts said they should be.

Beware of any aluminum type clamp which involves the formation of
the aluminum strap into a loop to fit the size of some tubing, and
clamped with a machine screw and nut. The shorting bars on KLM 40
meter antennas are this way, and they have caused me all sorts of
headaches. I'm still trying to figure a good design for those.

73, Rod N4SI
    The DXer formerly known as N9AKE
         (c) 5 November, 1996

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