[AMRadio] Open Wire - was AMRadio Digest, Vol 46, Issue 24

[Barrie Smith]

----- Original Message ----- 
From: "Robert Nickels" <W9RAN at oneradio.net>
To: "Discussion of AM Radio in the Amateur Service" 
<amradio at mailman.qth.net>
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