On Nov 7, 1:08*pm, "David" nospam@nospam wrote:
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.

They are both "problem" antennas.. The usual 5/8 GP
is a problem antenna because years ago some designer
decided to use 1/4 wave radials instead of 5/8 or even
3/4 wave.
And most ignore common mode issues.

The J Pole often suffers because most tend to ignore
common mode issues, which leads back to lame
incomplete antenna design. :/

Both can be greatly helped by adding decoupling
sections at and below the feed point.
The 5/8 antenna should be run as a collinear
with dual 5/8 elements.
And with a lower decoupling section.
The dual 5/8 collinear is more effective than any
half wave vertical, even if the half wave is decoupled
from the feed line.

BTW, I have no real issues feeding from a high voltage
point. And the loss in a 5/8 loading coil is probably
not enough to even measure for most people.
Both are non issues.
The real issue is lack of decoupling, and using a
perverted 5/8 over 1/4 wave element scheme in
the case of the usual 5/8 ground plane.

The perverted antenna design actually ruins the
pattern of what would be a decent antenna if it
were designed correctly with dual 5/8 elements.
Even running 3/4 wave sloping radials is much
better than using the usual 1/4 wave radials.

Of course, mobile 5/8 whips are only the upper
half of the antenna. They don't supply the lower
half in that case. For those, the vehicle is the
lower part of the antenna and performance can
vary from good to horrible depending on where
it's mounted.