On Wed, 13 Jul 2005 17:40:02 -0400, "Hal Rosser"
wrote:


I think he was correct about the half-wave length of feedline:
according to the ARRL Antenna Book - 17th edition copyright 1994 - page
24-12 in chapter 24, under the Heading "Special Cases" and under the
sub-heading "The Half-WaveLength Line", it pretty clearly states that
regardless of z, it will be the same on both ends of a half-wave line. and
sections having such length can be added or removed without changing the
load Z. (as long as loss is negligible)

Also - You don't need to know the VF if you use a dip meter (or MFJ 259) -
And he would want the length to be half-wave so as to be able to ignore the
characteristic impedence of the zip line and deal directly with the
impedence of the dipole directly.

This analysis seems to imply use of the antenna on only one one band.

Ill conceived alternative feed arrangments are the most common reason
why so-called G5RVs performs even poorer than the "genuine" article.

The original question about how well "Euro zip line" will perform will
depend on the characteristics of the line. I hazard a guess that it
will be unlikely to have a characteristic impedance as low as 75 ohms
as suggested by some, more likely 100 ohms or more. It is likely to be
PVC insulated, and lines of that type perform much poorer than a high
z line made of the same conductor, not just because of the dielectric
issue, but because the RF resistance of the conductor increases as the
spacing is reduced for very close spacings (proximity effect).

As to whether it "works" for you, you need to define your criteria for
"works". If "works" means you make some QSOs, then I am sure it
"works", but if "works" meand you want to deliver 80% plus of the
transmitter power to the "G5RV variant" antenna feedpoint on several
bands, then it is unlikely to "work".

For arguments sake, if the feedpoint Z of a 30.5m centre fed dipole
(G5RV length) on 3.6MHz is 10-j340, using the characteristics of US
Zip cord measured by K8ZOA, the loss in 25m of such feeder would be
13dB with a Zin of 563-61, so there would be some small
(insignificant) additional tuner loss. Is this what you mean by
"works"?

Owen
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