On 7/15/2010 9:52 PM, Sal M. Onella wrote:
On Jul 15, 12:33 pm,
wrote:
Peter Inscribed thus:

Hi all

I have just modelled both the Slim Jim antenna and J Pole antenna
using MMANA-GAL at the same frequency (145MHz) all other parameter
equal and was some what surprised that they appear exhibit the same
gain and radiation pattern. Based on an article I read in a English
magazine many years ago I have always believed the Slim Jim had a
slight edge over the J Pole. Wonder if others had a similar view and
if my modelling is correct are there any advantages with the Slim Jim
design?

The difference is negligible. They both suffer from unbalanced feed
currents and thus feeder radiation. There is or was a commercial
design that attempted to reduce that.

73's
--
Best Regards:
Baron.

I only did it once but the j-pole design papers often call for the
feedline to be coiled tightly -- a few turns -- just below the feed
point. I have made and used several of these "choke baluns" for HF
because failure to use a balun seems to screw up my VSWR readings.
Does this strictly apply to 2m j-poles, too? I don't know.

"Sal"
(KD6VKW)

I have used 7 turns on 1 inch PVC about an inch below the feedpoint on
the Arrow style J Poles I have built. I see no significant change in
the SWR when coupling my hand to the feedline over the first 2 meters
below the feedpoint on the 2 meter band. Per my version of "significant".

For best results, follow Roy's advice.

tom
K0TAR