On 3/31/2011 6:43 PM, tom wrote:
On 3/30/2011 12:23 PM, Tom Horne wrote:

Richard
I wanted to explore whether it is practical to have my collinear dual
half wave J-pole serve as a dual band antenna. If it were practical I
would want the same gain on seventy centimeters that I have been
getting out of the dual stacked half wave on two meters. The
available testing that I was able to find says that it is 6 DB over a
quarter wave vertical. What I would happily settle for would be for
it to have the same gain on seventy centimeters as the dual band
simple J-pole I am using now. After talking to Rol Anders, K3RA; who
was the instructor for my Extra theory class and is the present
chairman of the Question Pool Committee of the National Council of
Volunteer Examiner Coordinators (NCVEC); last night I am taking that
later approach. That is the approach that I outlined in the first
paragraph of just putting an open blocking stub for UHF at thirty five
centimeters ~ up the lower two meter half wave and therefore below the
two meter phasing stub between the two meter half wave segments. That
has the virtue of being simple and still giving me a dual band antenna
that has better gain on UHF then the unmodified two meter antenna
would.

I wanted a dual band antenna because I only have three suitable
mounting points on my home and I already have plans for a six meter J-
pole and an anemometer / sensor array assembly on the other two. I
have an Arrow dual band J-pole up on that mounting point right now but
I wanted to return to the higher gain of the collinear dual half wave
J-pole that gave me so much better real world performance on two
meters. It is my hope that just adding the seventy centimeter band
blocking stub to the collinear antenna's lower two meter half wave
segment will do the trick.

--
Tom Horne, W3TDH

http://www.arrowantenna.info/osj/j-pole.html

This design works moderately well. Drive the 19.25 inch element. The 51
inch element is the radiator on 2m, the 6.xx inch element makes the
19.25 inch one radiate on 440. The thing isn't great on 440 because the
51 inch portion is there. It is rugged though.

I built a duplicate, which you can do if you look at all the parts pages
on the site. The main problem, same as all J poles, is common mode
current issues on the feedline.

tom
K0TAR

Sorry, missed the part where you already have this antenna. My fault
for not reading the whole post until after I responded.

tom
K0TAR