[Antennas] Tuning Jpole question

Sun, 26 Jan 2003 12:58:55 -0600

Daniel,
I have read quite a few articles on making Jpoles, and the articles almost always
say cut it to these dimensions and it will work. Not much information on actually
tuning one to frequency. I have one in the attic made of a 19" piece of 450
ohm ladder line for the matching section and a 38" length of wire for the upper
radiator. It was tuned in place with an MFJ-259 Analyzer, and has great SWR
across the band, very flat in the middle and just rising to about 1:1.25 at
both top and bottom of the band. I cut the radiator so not sure of exact length.
It is fed with 50 ohm coax attached to an SO-239 about 2.5" inches from bottom.
I have also made several 1/2" copper pipe Jpoles and have had good success with
them as well. I could check for exact dimensions if you are interested.
73,
Darryl, KK5IB 
>   I just put up my first elevated external antenna... A 3/4" copper
>pipe Jpole for 2m operation...  I tried about 15-20 different position
>for the coax connection points and got it set at the point which gave
>the best overall swr.  The results are that I have an SWR of <1.1
>measured at 144.010mhz and an SWR of 1.7 at 147.990.  If I move the
>contact points up, the swr goes up across the board, move the contacts
>down and the swr goes up across the board.  My question is what should I
>do to move the low swr more towards the middle of the band or just lower
>it overall?  Do I need to chop some pipe off of the main  element or off
>of the stub or something similar?
>Thanks
>Daniel
>KC9DAG
>
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