[TowerTalk] Open Wire Feed

[Bill Coleman AA4LR]

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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