WOW, lots of data now.
For a while I was beginning to sway to the side of the Pin-1 problem.
However considering all of the new data you have given us, I am leaning
strongly to the transceiver possibly being defective, and second in line is
common mode current.
The best thing would be to find someone with an identical transceiver and
just swap it.
This may be impossible.
You didn't specify how you measured the current in the two wires of the
openwire. Do you have an RF Ammeter in-line with them, are you using lamps,
or how are you measuring?
How much imbalance is there?
If we knew for sure that it was not the transceiver, my next suggestion
would be to try two things on the antenna side.
<> First, I would disconnect the feedline from the dipole and connect it to
a 50 Ohm dummy load. Then match it in the shack with the JV Matchbox. If
the problem continues, it is probably something back at the house. Unless
it's the feedline. So you might want to check the feedline. Put a 4:1
balun at each end, connect a 50 Ohm dummy to one side and an analyzer to the
other. If no analyzer available, check it with a transceiver running low
power. Check 80m, 20m and 10m to make sure it's the same SWR across all
bands. Note: Most 50 Ohm dummy loads rise slightly in SWR on 10m so don't
let that trouble you.
<> Second, only when you have a dual-RF Ammeter inline so that you can
monitor it, I would record exactly how much current is in each leg with 10w
(a little more if you can), then begin shorting the leg of the antenna that
over the house. I would shorten it in increments of 6 inches. Check RF
current balance after each adjustment. WHEN I SAY 'SHORTEN', I do not mean
cut; simply fold it back from the insulator and wrap around the rest of the
wire, fixing it with a wire-tie. The goal is to get the current close to
equal (less than 10% difference) in each leg. If your problem is really
CMC, that just might solve it.
OTHER THINGS TO TRY:
<> Replace the coax between the transceiver and the JV Matchbox. Try it
both with and without the RF choke.
<> Replace the JV Matchbox with something else. Use a 1:1 current choke
between an asymmetrical matchbox and the openwire and try it on 80m. Don't
use the built in balun on any matchbox. There are very few on the market
that have the correct type of balun. Use a balun you know will work. This
is the last thing I would suspect, but sometimes... hey, in Oklahoma we've
even seen cows fly. Ya never know until you try.
<> Try another power supply.
<> Move your transceiver out into the back yard and run your openwire to
it. Try to keep the feedline at a 90 degree angle to the dipole.
One thing for sure: there's always a reason.
You just have to keep trying stuff until something shouts out at you and
gives you a clue.
One thing for sure Carter, you have one of the most interesting problems
we've seen here in a long time!
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Carter
Sent: Thursday, May 15, 2014 9:23 PM
To: tentec@contesting.com
Subject: Re: [TenTec] Eagle problem?
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
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