[Antennas] Twin lead 450 Ohm
Lefczik, Larry D
[email protected]
2002年12月11日 09:40:22 -0500
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