J Pole Antenna and SWR

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dksac2

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Greetings, this is my first post here, I've been a lurker for a while.

I bought one of the J pole antennas made from copper tubing from KB9VBR J Poles and my question is, if the SWR needs adjusting, what part of the antenna do I adjust ?

The center conductor feed point, the length of the short or long end of the two rods ? I'm just not sure where to start. I have a SWR meter, have only ever adjusted CB antennas in the past.
He has the centerpoint fitted to the long 1/2 wave radiator and the connector soldered to the short 1/4 wve radiator.

Thanks for your help, John
 

kc5uta

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Greetings, this is my first post here, I've been a lurker for a while.

I bought one of the J pole antennas made from copper tubing from KB9VBR J Poles and my question is, if the SWR needs adjusting, what part of the antenna do I adjust ?

The center conductor feed point, the length of the short or long end of the two rods ? I'm just not sure where to start. I have a SWR meter, have only ever adjusted CB antennas in the past.
He has the centerpoint fitted to the long 1/2 wave radiator and the connector soldered to the short 1/4 wve radiator.

Thanks for your help, John
I have built a LOT of J =poles. when I tune them I slide both contact points either up or down on the J (the bottom part making a "J" or the "hook". I try to keep them even. There are a few tricks as well. A "tuning" screw mounted in the top of the short piece, to fine tune, after you get the SWR as low as able with the feed points, is one option. Mine all have the center to the short end and shield to the long one though....but I have heard it doesn't make THAT big of a difference. (May be wrong though) I usually start at the bottom of the "J" and slowly work my way up. Good luck.....Dave
 

dksac2

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Thank you, I was pretty sure it was the feed point that got adjusted.

I really like your idea of the screw on top, an easy way to lengthen. I would guess if SWR got worse with the screw further out, it would be time to shorten the rod a little and start over fine tuning.
I'll most likely set the feed points as you have them. One last question, does the screw go on which ever rod the center conductor is soldered to ?

Thanks again for helping a new guy, I want to get my Tech license first, get on the air with 2 meters, then go for my general. I was thinking about 10 meters, but have been reading about some of the truckers interfearing by modifying or using 10 meter rigs unlicensed, I'd prefer to start somewhere with less people who were not licensed.
I plan on setting up the antenna and radio and monitoring until I get my ticket. It will give me a little experience prior to keying up the first time just by listening.
Time to study, I hear it's not that hard and have a little experience, just enough to be dangerous. LOL

My Best, John
 

kc5uta

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You can do both..... But the j pole is quite forgiving. Look up "super j" they are quite effective as well. Just remember to follow the basics . A half wave fed by a quarter wave section .... Look up "collinear" antenna as well have fun : )

Kc5uta....... Dave
 

kb2vxa

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The short answer is the distance from the bottom of the U to the feed point determines the feed point impedance. You may have to adjust it slightly for the best match and BTW the SWR reading is always taken at the antenna as feed-line length tends to upset the meter. Which leg does each lead go to? Doesn't matter, it all comes out in the wash.
 

dksac2

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More good info, I would have checked the SWR at the radio, not at the feed point at the antenna, sounds like it will make it a little more exciting to do.

Thanks for the info guys, I appriciate it more than I can say.

My Best, John
 

kb2vxa

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Pardon my giggles, HF and VHF/UHF meters are two completely different anamules. (spelling intentional) Now if you want a bridge (not a meter) that is accurate from DC to light anywhere in the transmission line Bird makes some interesting toys.

Thinking of the classic Bird 43 I'll never forget the klutzy FCC field engineer who tried to measure the power output of my CB with a 100W 450MHz slug... AFTER I pointed out he was trying to screw an N connector into the SO-239.
 

kc5uta

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.

I'll never forget the klutzy FCC field engineer who tried to measure the power output of my CB with a 100W 450MHz slug... AFTER I pointed out he was trying to screw an N connector into the SO-239.
NICE....now THAT'S funny...and a bit sad all at the same time. AND he was an FCC official????? Jeeeeez : (
 

dksac2

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That is funny. I got a Diamond SWR/Power meter for VHF/UHF, it covers the 2 M and 70CM range.

Thanks for the help guys. I got my ticket and a Yeasu FT60R handheld and a Diamond antenna for my truck. The area I live in a rural area, very little traffic in the area.
There is one repeater, which the radio hits with no problem, but hardly any traffic at all. I'll bet many of you in other area would like to have my problem.

Good thing is that 5 of us went to the exam and all got out Tech license. I didn't study for the general, took it for grins and missed getting it by 3 questions.

I'm glad I didn't pass as I really want to know all the theory, not just make a best guess, so I bought the ARRL General study guide as well as the Basic Electronics book and a couple others. I really want to learn all I can, joined the ARRL also. I plan in getting involved with the ham radio and our emergancy services in our area, it needs help here, so I'm going to do my best to get as many hams involved as possible. I'm going to start on the courses offered by the Government and ARRL.

My Best, John
 
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