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Old November 18th 08, 05:59 AM posted to rec.radio.amateur.antenna
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First recorded activity by RadioBanter: Jun 2006
Posts: 487
Default Is blockage of Jpole bottom stub ok?

Sal M. Onella wrote:
More musing: Does the entire "J" have to be upright? Can't I put an elbow
where the quarter-wave and half-wave sections meet, so the radiating element
is vertical, but the quarter-wave section is horizontal? (In the case of a
tower side-mount, this would position the radiating section a nice distance
from the tower. Inverted OK.)


Sal, I think that the position of the J affects its polarization. Around
1995, I did some informal experiments with an MFJ 300 ohm twinlead J-Pole
and 2m SSB. I used a Yaesu FT-290RII with 2 watts output.

At 2m, polarization is important and I found that by laying the J-Pole
horizontaly, I was able to extend the range of my signals, even if
I layed the antenna on a wood picnic table.

I did not experiment with the antenna in a mixed orientation as you describe
above.

Another posibility is to place a 300 ohm J-Pole antenna inside a rigid
PVC pipe. If the pipe is long enough, the base can be clamped without
affecting the antenna. This does move the feed line from being extended
horizontaly at the feed point to being extended verticaly downward, but
this did not seem to effect the antenna, and the MFJ unit I have is
designed that way.


The 450 ohm ladder line units I have made are built with a horizontal
feed, but that's more lazyness than anything else.

73,

Geoff.




--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
 
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