On 5/14/2014 6:32 PM, Rick - DJ0IP / NJ0IP wrote:
Carter,
>
> Most of the time this type of problem is caused by common mode
> current. I don't think the 25' away from the house is the problem.
> The problem would be an imbalance in the current on the feedline.
I suspect you are correct. This does not surprise me in that the antenna
itself (132 foot dipole at 25 feet above ground) is anything but
physically balanced. The dipole is not in a straight line (bent at about
70 degrees), half of the antenna is over grass, the other half passes
over the house, different halves are closer or further from trees, etc,
etc all due to the lay of the land and available mounting points (trees)
-- so, anything but "balanced". Unless you are very fortunate or have
your antenna in hypothetical free space, unequal currents i.e. feed line
radiation, is virtually unavoidable.
> I can't say whether or not something is wrong with your OMVI. Of
> course it is possible.
At this point, that seems to be the main suspect. I have been getting
input from a few sources (some of which shall remain nameless) that this
radio, at least in its early days, had the dreaded "Pin One" problem.
So that is the bush I was beating around: any specific, known cure for
an Omni VI Pin One problem... or any Yaecomwoods that are known to NOT
have a Pin One problem.
> However my recommendation is an RF choke on the openwire. YES, there
> is such an animal!
>
> I don't know if you can buy them ready-built in the states but you
> can buy them here. They are also very easy to build if you can't buy
> them. What you do is build a short thin openwire using two 18" pieces
> of Teflon insulated wire secured side by side. Use heat shrink tubing
> to secure them. They will have about 100 Ohms, but that doesn't
> matter for just 18 inches. Then slip a string of ferrite beads over
> them. Best would be #43 material. You can use the same ones used for
> RG-213.
As an aside, it sounds similar to the device I have on the input side of
the Johnson Matchbox -- a commercial device I bought years ago (can't
remember the name brand) -- that is a piece of coax about 18" long, the
diameter of RG-58, 50 ferrite beads covered with heat shrink.
Interesting idea to try a similar device on the antenna (open wire) side
of the tuner.
73,
Carter K8VT
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|