"David" nospam@nospam wrote in message
...

Which antenna is better: 5/8 wavelength vertical or a J pole?

Frequency of operation is 145 MHz = 2 metres.

The 5/8 wavelength vertical has a loading coil. There are losses in the
coil.

The J pole has a quarterwave matching stub. The matching stub provides an
out of phase current which means that there is a cancelling field close to
the radiating element. Also the J pole is end fed, which means the
transmitter is not connected directly to a maximum current point.

Does the J pole have a disadvantage because of the cancelling field from
the matching stub and the fact that it is end fed?

Also consider gain and angle of radiation.





I'm currently building a 5/8 wave ground plan for 2mx as a tower based
antenna, I have used J pole and slim jim type antennas in the past for the
same purpose with success. I would think that the 5/8 radiator may have
slight gain advantage, but believe that the J pole may have a slightly lower
angle of radiation. The J pole is certainly easier to construct as there is
a bit of mucking about with 1/8wave loading coil on the 5/8 antenna.
There has been much discussion about common mode currents produced on the
feed line for the J pole that can create an unpredictable radiation pattern
which is partly why I'm constructing the 5/8 and partly I'm building a 5/8
ground plan as I have never built one before.

Build both and compare.

If the antenna is for mobile I would certainly use the 5/8 antenna.


--
Peter VK6YSF

http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm