There is no benefit in eliminating the balanced line from the house - other
than it may be physically easier to route. Nor does it help "leave the RF
outside."
Coax is no better in the presence of common mode current than openwire, in
fact, sometimes it's worse.
If you can twist the openwire once or twice per meter (3 ft.), then it often
cancels the CMC out. You can't do that with coax.
If the problem is being caused by common mode current, then switching to
coax doesn't help.
Adding an RF choke (what Mike is calling a line isolator) helps, but you can
add that to coax or openwire in the same way and it accomplishes the same
thing.
Common mode current is caused by an imbalance of RF current in (and on) the
feedline. It may be caused by an imbalance at the feedpoint, or by direct
radiation back into the feedline - or both. If it is being caused by
radiation into the feedline (which is likely in Carter's case), then
inserting a current balun outside, away from the house won't help. The CMC
just radiates onto the coax on the house side of the balun and continues on
its merry way to the TX.
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Mike
Schatzberg
Sent: Thursday, May 15, 2014 1:17 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Eagle problem?
Hello Carter,
Why not eliminate the balanced line near the house?
Install a 4:1 current balun on the balanced line well away from the house,
and connect from the balun to your tuner with 50 ohm coax. Bring it thru the
wall and have nothing radiating in the shack.
A line isolator can also be installed right before the Eagle.
I sit under a fan dipole and have no issues with 100 watts portable.
Naturally, a good single point ground with a short low impedance ground
connection is desirable, but I operate at the beach from the second floor
without it.
Leave the RF outside.
73,
Mike
W2AJI
Sent from my iPhone
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