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 can't say whether or not something is wrong with your OMVI.
Of course it is possible.
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.
Use wire ties each side of the stack of toroids to prevent slippage.
You can then place a large heat-shrink tube over the thing to make it look
neat.
Run your openwire into one end of this just before the matchbox.
The connect the other end directly to the JV matchbox.
There is a good chance that this will solve your problem, but of course I
can't promise it.
With just 100w, Teflon insulation may not be necessary but it should be
something that can withstand a little bit of heat without melting.
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Carter
Sent: Wednesday, May 14, 2014 10:36 PM
To: tentec@contesting.com
Subject: Re: [TenTec] Eagle problem?
On 5/8/2014 6:51 PM, Stuart Rohre wrote:
> These types of problems usually indicate that there is RF leaking
> back to any any transceiver he might try, because his antenna is too >
close to the shack ...
An interesting thought, but can we always blame the "antenna being too close
to the shack"?
I bought my Omni VI new in 1994 and have never been able to operate SSB or
PSK31, SSTV or any other mode that required the use of the mic jack.
(Good thing I am 99% a CW and RTTY guy. <grin> ) Anything over about 10
(ten) watts of power seems to cause the problem, utter and complete
distortion of the radiated signal.
The shack is in the basement, the antenna is a 132' long dipole about 25
feet high and fed with ladder (window) line to a Johnson KW Matchbox tuner.
The length of the window line between the Matchbox and the hole in the wall
where it exits the basement is no more than five feet. Yes, when I measure
the RF current in each leg of the window line they are different -- to be
expected as this is not a perfect world and the dipole is not in free space.
The coax cable to the Centurion / Omni VI has a multiple ferrite bead balun.
After years of unsuccessfully chasing around with ferrite beads and chokes,
I was finally told [by ******] that my dipole was "too close to the house".
Unfortunately, because of the shape of the lot, the location of trees and
zoning/deed restrictions, the antenna HAS to be where it is.
So...problem occurs at around 10 watts of output, the antenna can't be moved
and I don't think I am the only ham in the world using a dipole close to the
house fed with window line.
This leads me to do the unthinkable and to ask about the elephant in the
room. Rather than everyone saying the antenna "is too close to the house",
is it possible that this particular vintage of Omni VI option 3 is just
particularly sensitive to RF getting into the mic jack (or other ports)???
Is this unique to my radio? Do Yaecomwoods suffer from the same issue?
The reason I ask is that I am getting into PSK31, JT9 and JT65-HF (and yes,
I realize these are "low power" modes), but I wouldn't mind going up to 20
or 25 watts -- or SSTV at (gasp!)100 watts.
I would appreciate any thoughts or suggestions. New /different radio or
fixing this radio (how?) is OK, but a 100' tower 300' away is just not an
option.
73,
Carter K8VT
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|