[Antennas] VHF J-Pole and Slim-Jim on UHF

[Chris Boone]

The J Pole is actually an end fed 1/2wl Zepp antenna with a quarter wave
matching stub (popular on HF with ladder line feeding it and used on
multiple bands with a tuner)...this makes the antenna "look" 3/4wave
electrically.....but stays 1/2wl physically to keep the lower angle of
radiation....(in my opinion a J is not worth the effort since the gain of it
over a normal 1/4wave is not that much, and the 1/4wave ground plane is
easier to build...

The 3/4wave on 2m would be a 9/4 wave on UHF and would have a low Z feed
since it is an odd multiple...BUT the radiation pattern is hardly worth
it...a 1/4wave on UHF would probably work better than the 2m J...just
because the SWR is low doesn't mean it radiates worth a flip....If they
checked a normal 1/4wave on UHF vs the 2m J on UHF, they'll see the
difference.....

I often run a 1/4wave 2m on UHF on van rooftops, etc since they can take
trees limbs and parking garages better :)

Chris
WB5ITT

-----Original Message-----
From: antennas-bounces at mailman.qth.net
[mailto:antennas-bounces at mailman.qth.net] On Behalf Of Deon Erwin ZS1ZL
Sent: Saturday, November 15, 2008 12:50 PM
To: Reflector Antennas Qth.net
Subject: [Antennas] VHF J-Pole and Slim-Jim on UHF

A 2m 1/4 wave antenna can be used as a 70cm 3/4 wave antenna.  The antenna
presents a low impedance on both bands and one only has to consider the
change in radiation pattern, making it an effective dual-band antenna.

There is a lot of local debate over the use of a 2m J-Pole or Slim-Jim on
the 70cm band.  In the 2m 1/4 wave example, the antenna is an odd multiple
of 1/4 waves on 70cm.  The J-Pole is a 1/2 wave on 2m, resulting in
something completely different on 70cm.

Some local hams claim that the 2m J-Pole or Slim-Jim also functions as a
dual-band antenna, just like the 1/4 wave example.  Surely this is 
incorrect?

Deon ZS1ZL
ilman.qth.net