----- Original Message -----
From: "Robert Nickels" <[EMAIL PROTECTED]>
To: "Discussion of AM Radio in the Amateur Service"
<[email protected]>
Sent: Wednesday, November 14, 2007 9:10 AM
Subject: Re: [AMRadio] Open Wire - was AMRadio Digest, Vol 46, Issue 24
Ben Dover wrote:
I personally love the stuff. Coax has it's place, but often it's not the
best solution to the problem.
I've always used coax, but wanted to give open wire a try, and so far I'm
very pleased with it. But let's talk tuners for a minute, assuming that
we're not directly coupling to a balanced plate tank. I've been running
1500 watts PEP into a Heathkit SA-2060 with it's 4:1 balun without
incident, but I've heard all the stories about core saturation, etc.
How much advantage would a "real" balanced line tuner (e.g. a link-coupled
tuner or Johnson Matchbox) have? Then antenna by the way is 130 ft,
center fed, and primarily used on 75 meters.
Also, having read comments by Cebik and others - any thoughts on
homebrewing high-power balanced tuners?
Thanks and 73,
Bob W9RAN
Bob & All:
Several years ago I ran across the Cebik tutorials on building true balanced
tuners and decided to build one.
Mine ended up being very large (3' X 3' X 3'), but quite capable, with a 210
pf per section butterfly and 7000 volt dual-differential output caps. The
link cap is a 3000 pf, 5000 volt vacuum cap.
I use BC-610 plug-in coils on 40, 80 and 160 meters, which are the only
bands I use.
According to Cebik, the true balanced tuner is very much more efficient than
tuners using baluns. I believe he states something around 60% for balun
tuners, and over 90% efficiency for the link-coupled flavor.
I have a Nye-Viking MBV-A tuner, which uses a balun. When running a couple
of KW, the MBV-A runs HOT. I've run 3.5 KW, into an air-cooled, wire
dummy-load with no sign of warming with my HB tuner.
I use a 400' doublet, with 600 ohm line. No need to cut anything to a
particular length, excepting, of course, that each half is the same length.
I can tune-up, with less than 1.2 SWR, on any portion of 40, 80 and 160
meters. And, with the Cebik design, the BC station images on 75 and 160 are
essentially non-existant.
I have had no reports of RFI from neighbors, nor from my XYL.
I had fun building the contraption, and I have fun using it.
73, Barrie, W7ALW
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