[TowerTalk] Re: twinax

Mark . n1lo@hotmail.com
Tue, 30 May 2000 09:35:59 EDT

Robert wrote:
<< It there any good use for twinax for antennas?  We have miles of the 
stuff all over our wineries that has been decommissioned.  Is it worth 
bringing home? >>

Hi Rob,
If I understand the term twinax, and you are referring to two coaxial 
cables, having separate shields and molded together in the same jacket, then 
the answer is yes, definitely!
This can be used for shielded parallel transmission line, as described in 
the ARRL antenna handbook, and is my favorite way to bring parallel 
feedlines into the shack, straight to a tuner.
The coaxial lines can be connectorized and brought through a grounded 
entrance panel, allowing easy disconnection and shorting when not operating.
Shielded parallel line can be run next to metal objects or through conduit.
Typically, you would bring your parallel line to the shack window, then use 
the shortest length of shielded parallel line required to connect to your 
tuner (assuming your tuner has a balun).
The effective impedance of the shielded parallel line is twice the 
characteristic impedance of one of the coaxial lines.


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