[Antennas] Simple dipole

[Ed - K9EW]

Hi Bill,

It's tempting to try using it like the old TV lead in you refer to, but a
first a few thoughts...

You don't know the impedance, dielectric constant, or the loss of the line,
so there's some risk involved.

Probably the safest attempt would be to split the line so that you have a
quarter wavelength (standard formula) of each conductor for the top of your
dipole.  Then, since you don't know the dielectric coefficient, extend the
unsplit part of the lead in for a half-wavelength beyond where the two legs
fan out (the center of your dipole).  Then start trimming it back for a good
SWR (1.4:1 would be ideal since a dipole feedpoint impedance is 72 ohms, and
your rig is 50 ohms).  Depending on the dielectric, that sweet spot will
probably be a length of 70 - 80% of the full half-wavelength.  The idea
behind this "twinlead dipole" is that when your feedline is an *electrical*
half-wavelength it's as if your rig is right at the feedpoint of the dipole.

If you have an antenna analyzer, or have a friend with one, the whole
process becomes easier.  In fact, you can characterize the "twinlead", and
decide how/if you want to use it.

This reply isn't quite as simple as the dipole, but I hope it answers your
question.

73,
ed - k9ew



On 4/1/06, Bill Barr <n4uaj at mac.com> wrote:
>
> Due to construction behind my qth I ran across a bunch of what
> appears to be some of Ma Bell's old transmission line that had ran
> overhead before they went to burying it all. My question is would it
> be ok to use both conductors as one leg of a dipole or would I be
> better off to split it and use a single conductor for each side..It
> is solid copper wire spaced about the same as old flat tv wire but
> much heavier.
>
> Thanks
>
> Bill
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