[Antennas] Twin lead 450 Ohm

Wed, 11 Dec 2002 12:12:06 -0500

Hi,

Why don't you guys use 300 ohm ladder line?  Smaller, approximately the 
same loss as 450, and of course, it takes a smaller tube.

At 09:40 AM 12/11/2002 -0500, Lefczik, Larry D wrote:
>If you run twin lead near any thing there will be a change of impedance in
>the area of the thing.  A change in impedance along a transmission line
>causes reflections.
>
>With the twinlead suspended 5 inches from the PVC pipe and 5 1/4 inches from
>dirt the impedance of the line will change.  How much of a change is
>determined by the dielectric constants of the air in the pipe, the
>dielectric constants of the pipe, and dielectric constants of the dirt.
>
>As stated here before, you want to keep water out of the pipe. You may want
>to plug each end to keep critters out of the shack - here again is another
>"thing" that the twinlead will be near.
>
>The question becomes, will the impedance change(s) be enough to cause a
>large reflection(s), hence, a high SWR where the twinlead enters and exits
>the pipe?
>
>With a 10 inch PVC pipe, if you can keep the twinlead suspended in the
>center, I don't think you will see any problems.  Remember, it's Amateur
>radio, a small loss from a small reflection will not be noticed by anyone.
>
>
>Let us know how you plan to suspend the twinlead and let us know any
>measured results.
>
>73 de NJ2L
>- - -
>
>Your moderator for this list is:
>Larry Wilson KE1HZ [email protected]
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73, Chas, W1CG
K2 #462