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Re: HIGH SWR ON M^2 2MCP22 YAGI



At 10:13 AM 10/3/98 -0700, A. R. MAERTZ wrote: 
>
> I have an M^2 yagi--2MCP22 and am reading an SWR of 4:1 on it.  I am
> measuring it with an MFJ-259B. I do get a slight dip at its (supposed)
> resonant frequency, but only slight.  I have triple checked construction,
> replaced and tested with new feedine (9913 with N connector, of course), but
> SWR remains high.  M^2 states VSWR will be 1.4 max.  I have the beam elements
> rotated to 45 degrees (elements to earth plane), but that was suggested in
> construction literature.  
>  
> Has anyone else experienced difficulty with this antenna?


I had a problem with one, new out of the box.  There was a problem
with the solder joint inside the little machined-aluminum cube that
joins the single feedline to the two driven element feeds.

This was on Field Day a few years ago, and the antennas weren't
mine, so I no longer have access to them or to the paperwork, so
I'm relying on my memory for the details.  My recollection is that
the cube was sealed with goo.  It is strictly a T-adapter electrically
so you should be able to confirm or refute this theory with an
ohmmeter.  Check that the input center pin is actually connected
to both output center pins.  If not, either you've found the problem
or else I've made a mistake in remembering.

In my case, the result *at the antenna* was an essentially
infinite SWR (measured above 10:1).  However, at the shack
end of the feedline, it only looked like about 5:1, and that was
with a short Field-Day style feedline.  If you're running about
70 feet of 9913 into the shack (that's how long my run is at
home) a measured SWR of 4:1 in the shack probably means
that SWR is infinite at the antenna, and the lower figure is due
to the loss in the feedline.  This is the same thing you'd see if
the antenna wasn't even connected, which is an experiment
you might try running.  Other possible causes include a badly
assembled N connector at the top end of the coax, such that
the center pin isn't making contact.

Since it was Field Day setup (Friday after business hours) and
we needed it to work right then, we had to dig into the cube,
remove the goo, and resolder it.  Messy.  But on Monday we
called M2 and they were apologetic and happy to ship us a
brand new cube.

73  -Paul
kb5mu@amsat.org


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