[TowerTalk] Open Wire Feed

[Michael Tope]

I just wanted to relate a little vignette with regard to baluns. Back in 1984, 
I purchased and built a Ten-Tec 4229 "2KW" tuner. The tuner was equipped 
with a small 4:1 balun (Ruthroff type I believe). When used with my barefoot 
C-Line, this worked great. At the time, I was feeding an flatop dipole at 45 feet 
with 450 ohm ladder line.

Soon after getting the tuner, I decided I was ready for QRO (I wanted to try 
my hand at low band Dxing). I borrowed an apartment bound friends SB-220 
(NZ4K, now N8VW)  and went on the air. Within 5 minutes of tuning up on 75 
meters, the 4:1 balun was cooked. Furious, I called Ten-Tec to complain about 
the failure of their "2KW balun". I ended up speaking with chief engineer  Dick 
Frey, K4XU. Dick patiently tried to explain to a then indignant know it all kid, that 
the 2KW rating on the balun only applied over a fairly narrow range of impedances. 
This was my first introduction to the limitations of ferrite baluns. Undettered, I 
acquired a three high stack of Amidon T-200 "Red Mix" Iron Powder Torroids from 
a fellow in the Columbus, Ohio area (I think they were left over from 3-1000Z project). 
The stack was wrapped with a layer of fiberglass tape over which I wound a 4:1 
voltage balun with some #14 AWG solid house wire that I had laying around. The 
balun was so big that it barely fit inside of the tuner. 

With the same impedance mismatch that had smoked the little Ten-Tec balun,  I 
was now able to run full smoke from the SB-220 (about 1300 watts on my sagging 
110 line). I have no idea if I had the correct number of turns on the balun or if the 
balance was any good (my design philosophy was to make it look cool). All I cared 
about at the time, was that the "Red Stack" didn't go up in smoke when I went hit it 
with the 1300 watts from my friends Heathkit amp. As a matter fact, the "Red Stack"
barely warmed where the other balun had failed. The same tuner was later used to 
match W8LT's famous 600' long wire at Ohio State on 160 meters. The "Red Stack" 
balun never complained. 

BTW, I understand that the original owner and builder of the SB-220 I was using was 
the famous contester and CQ columnist, John Dorr, K1AR. Small world, eh?

73 de Mike, W4EF........................................
 

----- Original Message ----- 
From: "Bill Coleman AA4LR" <aa4lr@radio.org>
To: "K7HPH" <k7hph@xmission.com>; <towertalk@contesting.com>
Sent: Wednesday, October 04, 2000 10:49 AM
Subject: Re: [TowerTalk] Open Wire Feed


> 
> On 10/1/00 6:19 PM, K7HPH at k7hph@xmission.com wrote:
> 
> >I have an 80 Meter Dipole fed with 450 ohm ladder line. At my
> >new house, I must run my coax rotor cable, etc. through a 20 foot 3 inch
> >conduit to get to the shack. I am thinking that I need to terminate the
> >ladder line to a balun designed for such applications and run the coax
> >output through the conduit to the antenna tuner to run multi-bands on the
> >dipole.
> 
> This is known as a remote balun. I have a similar installation at my 
> house. It works great. A few notes:
> 
> 1) Use only solid dielectric coax for the tuner to remote balun run. 
> Since you may have a complex impedance on this run of coax, it is 
> important to keep the voltage breakdown of the coax high. Foam insulated 
> coax has a much lower voltage breakdown. I use RG-213 for this run.
> 
> 2) Use the shortest length practical for the coax run. Again, with the 
> complex impedance, you're going to incur greater loss in the coax. Keep 
> it short to minimize losses.
> 
> 3) Use a big balun. Typical toroidial balun cores can get lossy when 
> dealing with complex impedances. Don't fret about the turns ratio -- with 
> a complex impedance, a 4:1 or 1:1 works equally well. Use a core that is 
> much bigger than you would for a resistive load. I run 100 watts, and use 
> a 2 kW balun. use a 5 kW design for a full gallon. Check your 
> installation on multiple bands with power. You shouldn't see any 
> appreciable heating on any band.
> 
> While the remote balun doesn't have the same low-loss characteristics of 
> an all-open-wire installation, it is much easier to route the 
> transmission lines into the structure, and retains many of the advantages.
> 
> 
> 
> Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@radio.org
> Quote: "Boot, you transistorized tormentor! Boot!"
>             -- Archibald Asparagus, VeggieTales
> 
> 
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> 
> 


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