"tjs" wrote in message ...
I have a 40meter band xmit/recv antenna up with good swr and works great.
Cost me nothing but my time, and a plastic center insulator to strain
releive the zip cord (rather than tie a knot in the cord at the center. Just
rip down 33 ft of zip cord, tie a knot or use the insulator, and cut the
feedlinne section to a integral half wave long (20, 40, 60etc meters long).
If cut to a half wave (use a dip meter) the swr of the dipole will be
translated unaltered to the radio end of your feedline and 70 ohms is OK for
a swr of 1.4 and the xcvr will not care usually.

Great emergency antenna.

Why do you think the SWR of the dipole will be unaltered at the radio end of the feedline? You are apparently ignoring the loss in the line that makes the SWR at the radio end less than that at the dipole terminals.

If the zip cord had zero loss the SWR would be the same everywhere along the line, only the terminal impedance at the radio end would be the same as at the dipole.

Without knowing the vf (velocity factor) of the zip cord how do you determine that the length is a half wave?

And last, why would you want the length to be a half wave?

Walt, W2DU


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