Where to measure from when building antennas

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Trprc

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Jan 28, 2012
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Hi Guys,

I have all the material to build a J-Pole 2 Meter Antenna.

I have looked at all of the designs and drawings. Its a bit confusing since I am not sure where the measurement reference points are.

Are the measurements be done from the centerline of the pipes or inside to inside?

Please take a look here and tell me what you think.

Is also advisable to bulild the antenna for 146 Mhz since I will be using between 144 and 148 MHZ, better to go in the middle?

2 Meter Jpole Page

2 Meter J-pole Antenna Construction Plans

Building A 2-meter J-Pole Antenna


Thanks Guys.

73
 

r_eugene1

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Jun 20, 2011
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Location
Southwest Ohio
Hi Guys,

I have all the material to build a J-Pole 2 Meter Antenna.

I have looked at all of the designs and drawings. Its a bit confusing since I am not sure where the measurement reference points are.

Are the measurements be done from the centerline of the pipes or inside to inside?

Please take a look here and tell me what you think.

Is also advisable to bulild the antenna for 146 Mhz since I will be using between 144 and 148 MHZ, better to go in the middle?

2 Meter Jpole Page

2 Meter J-pole Antenna Construction Plans

Building A 2-meter J-Pole Antenna


Thanks Guys.

73
I would build the antenna for the center of 2 meters which is 146.000 next I would go to measuring on the inside of the copper elbows since 2 of the 3 diagrams show the measurements from the inside bends of the elbows.
Good luck on your build as I have just recently built a 2 meter vertical antenna using a SO-239 chassis mount connector and #12 copper wire. I have been able to get repeaters as far a 40-60 mile from me all 4 directions with on a height of 15' .
 

LtDoc

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Oklahoma
The last link given seems to be fairly 'exact'.
There's no 'one-way' to build a 'J'-pole, and it will have to be tuned when completed anyway. So, being super-exact isn't going to always put you where you want to be. That especially holds true for the feed point(s) of a 'J'-pole. Moving those attachment points slightly one way or the other can make a lot of difference.
It's a sort of good idea to make the 'elements' of that 'J'-pole slightly longer than necessary. That gives you some 'tuning-room' to play with. It's much easier to remove than to add to.
- 'Doc
 

Trprc

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Jan 28, 2012
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Thanks Guys,

I built the J Pole antenna, we tuned it with an alalizer and she works like a charm, really great numbers right accorss the spectrum.

Thanks for the input guys.


73
 

DcotorWu

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Feb 15, 2012
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It really is not that critical. I'd just do it from one side of the pipe to the other. 1/2 inch aint critical at all...in fact, when you are talking about jpole spacing, probably 2 inches would not matter. The antenna will still tune up to minimum SWR. All you need to do when tuning the antenna is move the connector contact points up and down the bottom section and find the sweet spot.

73 and good luck!

Doc
 

Trprc

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It really is not that critical. I'd just do it from one side of the pipe to the other. 1/2 inch aint critical at all...in fact, when you are talking about jpole spacing, probably 2 inches would not matter. The antenna will still tune up to minimum SWR. All you need to do when tuning the antenna is move the connector contact points up and down the bottom section and find the sweet spot.

73 and good luck!

Doc
Thanks Doc,

I did that, see my post above yours.

73
 

BJ_NORTON

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409
Location
Las Vegas
I've been thinking about building one of those too, but I wonder about the feed point. How did you connect the cable to the pipe? I've seen lots of discussion about using an SO-239 connector, but never figured out how one might connect a flat panel mount connector to a round pipe. How did you do it? Any pictures?
 

Trprc

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Jan 28, 2012
Messages
74
I've been thinking about building one of those too, but I wonder about the feed point. How did you connect the cable to the pipe? I've seen lots of discussion about using an SO-239 connector, but never figured out how one might connect a flat panel mount connector to a round pipe. How did you do it? Any pictures?
You could solder just a corner of the connector to the pipe but I would suggest soldering the coax onto the antenna itself.

It is important to use an SWR or an analizer (ask the guys in your local club) to help you tune the antenna. We spent over two hours, cutiing the antenna and adjusting the coax placement for a perfect SWR ratio.

So to answer your question about how the coax was attached, as mentioned in my first sentence, I slodered them directly onto the antenna.

We made a nice choke using a few turns with the coax and noticed that even the position of that in relation to the J-Pole, the SWR ratio varied.

I will see if I have photos of the soldered connection.

The J-Pole is a great, cheap, simple and mauntenance free antenna, the difficulty you will face is aligning everything and being able to solder the parts togeather without melting the solder on another joint. I was using a propane torch and had to be careful, I do have have soldering and welding experience so that helped.

One of the disadvantages of soldering the coax to the feed points is the fact that you can melt the soler on the joints. You will also melt the coax too by that time. I made a simple jig and everything went OK.

If you need anymore info let me know but many examples and pics are on the net as well.

73
 
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LtDoc

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Pssst - Another 'nice' thing about a typical 2 meter 'J'-pole is that it is usable on 70 Cm. The key word in that is 'usable'. It isn't going to be great on 70 Cm, but it will certainly work without the typical dual-band radio really raising a 'stink' about it. I figure it works as well as a common 70 Cm 1/4 wave antenna so don't expect some kind of 'magic' results, you know?
- 'Doc

(Did I 'invent' this? Yeah, right! Just like 'whats-his-name' invented the internet.)
 

DcotorWu

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Feb 15, 2012
Messages
24
You could solder just a corner of the connector to the pipe but I would suggest soldering the coax onto the antenna itself.

It is important to use an SWR or an analizer (ask the guys in your local club) to help you tune the antenna. We spent over two hours, cutiing the antenna and adjusting the coax placement for a perfect SWR ratio.

So to answer your question about how the coax was attached, as mentioned in my first sentence, I slodered them directly onto the antenna.

We made a nice choke using a few turns with the coax and noticed that even the position of that in relation to the J-Pole, the SWR ratio varied.

I will see if I have photos of the soldered connection.

The J-Pole is a great, cheap, simple and mauntenance free antenna, the difficulty you will face is aligning everything and being able to solder the parts togeather without melting the solder on another joint. I was using a propane torch and had to be careful, I do have have soldering and welding experience so that helped.

One of the disadvantages of soldering the coax to the feed points is the fact that you can melt the soler on the joints. You will also melt the coax too by that time. I made a simple jig and everything went OK.

If you need anymore info let me know but many examples and pics are on the net as well.

73
Trprc, so right on all of your last post. My complaint with these soldered jpoles is that you dont have to solder a thing in the first place. This whole deal has taken off over the years to the point of being ridiculous. I guess I am gonna have to draw, build and photograph a project and send it to the group files on how to build a solderless jpole for cheaper money. Also, you dont have to solder the coax on if you use hose clamps on each side of the feedpoint. Just weatherproof the whole assembly well.

I have built ground plane antennas for 2 meters and 440 mHz from old coathangers, and they perform just as good as a jpole built for much more money. How about a 50 cent 2 meter groundplane? A scrap of PVC pipe, some wire, and a few plastic cable ties? Weighs about 1/2 a pound, can be attached to a mast with duct tape, will last for years.

How about a jpole made out of old curtain rods? The rods are cheap steel and rust easily, so all you do is buy a can of rustoleum spray and zap it good after you finish. So what if it rusts up too much after 10 years? Anyway, every ham should have a couple of cans of rustoleum on the shelf. :)

It seems to me that there is a trend toward lock step building. I mean by that to say that some folks get the idea that if it isn't done like on the internet it won't work. Well, all I can say is that if you think like that just remember that you are making yourself poorer and Home Depot richer.

Just get in touch with me off the group and I'll give you plenty of simple ideas for antennas. Antennas are my obsession. All my antennas are homebrew, and I have worked the world with 25 watts. Email olekeykollekter at yahoo dot com and put antennas in your subject line.

73 Wu
 
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