J-Pole Antenna

[Jaymom]

I have built a J-Pole antenna exactly as shown on the following web site...

2 Meter J-pole Antenna Construction Plans

It can be seen here....

Family Home Page

It is supposed to show a SWR of 1.2 or so at 146.000 from what I can figure out. Instead I get a off the scales reading no matter where I go on 2 meters.

I have tried 144.000 to 148.000 and get the same readings, meter pegged to the right. I have checked the RG-58 coax, both from the antenna to the SWR meter and also from the SWR meter to my ICOM TM-271 and they are not shorted out. I can't even get someone on my local repeater to respond to my calls yet they are 599.

Someone on this forum must have built one of these one time or another and has an idea of what I am doing wrong. Any ideas will be much appreciated.

Harold

 

[W5LZ]

I think you might try connecting the feed line a little differently. Those 'leads' from where the center conductor is separated from the shield (center conductor and the shield) are contributing to the 'length' of the antenna's two 'elements'. Clamp the braid to one element and extend the center conductor straight across to the other element and clamp it. (It doesn't really mater which element the braid is connected to, but attaching it to the longer one brings the weight of the feed line more 'in-line' with the support, doesn't hang any additional weight on the short element.) That ought to get you at least into the ball park. Sliding those clamps up/down should get you to where you want to be.
That's about the only thing I can see that 'I' might do differently. Hope it works for you.
- 'Doc

 

[Jaymom]

Thanks Doc,,,,It's in the high 80's here in Ocala and I just came back in from trying everything I can think of including your suggestion. I have a huge headache too. I just wish I had a grid dip meter. I looked them up on the internet and they don't come cheap. Now I'm going to wait until tomorrow morning and play with it some more.

Appreciate it Doc,

Harold

 

[kd-5-bgt]

I would also do the connection to the antenna differently.

I took a chassie mount so-239 and connected the so239 to the ground side of the antenna with a metal stud framing screw through one of the holes in the so 239 and then soldered the mount,screw and antenna...

make sure the center conductor on the so239 is not going to contact the antenna....

then I used a short piece of the coax center wire and soldered it to the center conductor of the so239 and to the driven element with another short metal stud framing screw ..(use no more wire here than needed) and soldered that end as well...

Just snug the screws the solder will hold everything on place....The copper pipe is pretty soft and it wont take to much to strip out the screws

I ran my jpole I bet for 3 years or better and never had a single issue

 

[Jaymom]

Thanks for the idea kd-5-bgt. I just got a phone call so now i'll be going to the doctors office instead of doing what I want and that is working on my antenna tomorrow morning. So, maybe Friday morning. I just can't believe that this antenna is so far off resonance but it is.

I sure appreciate this forum. I've learned a lot here.

Harold

 

[Captain Kilowatt]

FWIW I concur with Doc. I connected the braid directly to the longer piece using just enough to make the connection and then extended the center of the coax over to the other side using just enough to reach. By doing it the way you did, in effect you lengthened the overall antenna dimensions and that is why you could not get it to match. On VHF a little sometimes means a lot.

 

[BOOTY MONSTER]

I'm going to say something and I want you all to remember that Jesus was hung on the cross for speaking his mind.

i thought it was to save folks souls ????????
a lot of folks are gonna be disappointed to find out he was just another big mouth that pissed off the wrong person .

 

[Captain Kilowatt]

Way to go Channel jumper. Bash a newbie for actually taking initiative to experiment and do something for himself. Did it ever occur to you that maybe some people get satisfaction out of building things for themselves and that perhaps even the lowly J-Pole antenna serves all his needs and wants? If all someone wants to do is access a few local repeaters than an antenna cobbled from a few bits of recycled coat hangers is perfect. It's NOT about what YOU want from HIS station, it's what HE wants from HIS station.

Having said the above I will say that there are a lot of people that have no idea what a good antenna is and most newbies end up using a J-Pole and a G5RV to start off with and think they are great. Later they end up finding out just what the shortcomings of these antenna are and acquire bigger and better antennas. We all have to start off somewhere.

BTW, if you think a discone antenna is great then it proves you don't know as much about antennas as you think you do. The ONLY good thing about a discone is the wide bandwidth they offer. They offer next to nothing for gain.

 

[W5LZ]

Channel Jumper,
After boiling what you said down, it seems you are recommending spending lots of money for an impractical solution to a simple tuning problem. Then you give an example of an antenna you think well of since that's what you use. I think after careful consideration that you just shot your self in the foot. You just contradicted the majority of what you just suggested as a 'solution' to that tuning problem. You are right though, that 'J'-pole has zero gain. The problem is that your well thought of discone antenna has a negative gain when compared to that 'J'-pole. As an 'RF engineer' you should know better than that, shouldn't you?
I also have to admit that you have a pretty nice grasp of 'spin' and 'hooks' with presentation of incorrect information...
- 'Doc

 

[kor b]

I'm thinking of selling my house real cheap, and buy a house on the hill.

 

[jazzsinger]

The whole purpose of ham radio is to learn about these things and to try to improve your mode of communications and to perfect your radio set ups so you can be a efficient member of the radio community and if there is a emergency you can help out with your radio communications.

that one paragraph contradicts everything you have said. ham radio is about learning,the best way to learn is to do it yourself, not run down to the local radio store for a brand new shiny antenna that some company mass produces in some third world nation or buying off the shelf radios, i think you have completely missed the point what amateur radio is all about.


as for emergency comms, i hope i never have to depend on a radio ham to save my life, many of them can't even solder a pl plug properly thanks in the most part to the dumbing down of testing.

at least jaymon is making the effort to learn, something that those who fill shop owners wallets rarely do.

oh and jesus is a figment of imagination in deranged minds, despite there being plenty of records kept in that area of population at the time he was never registered, i wonder why? maybe just maybe because he never ever existed.

 

[bob85]

a diamond discone is ok for a scanner or as an emergency standby antenna,
my diamond d-130 performs as well as a 1 dollar coat-hanger dipole but works from 6mtrs upwards with a reasonable vswr,

a j-pole can work surprisingly well for hitting repeaters, yes better than commercial 5/8waves for some people,

many hams like to experiment making their own antennas while others prefere to build their own cross,
would you like to buy some emperor claudius ( ad43 - 54 ) roman nails i dug up while metal detecting, they are rusty but i recon they will hold ya,

how about some road metaling from ermine street with 2000yo roman wheel ruts, as surveyed by julius ceasar ( bc100-bc44 )
i think you would find that ideal for stoning the locals who use handhelds.

 

[W5LZ]

How about that, a half wave over a half wave. So what wave length is that 'disk' made, and what 1/2 wave length is that 'cone' made for?
- Doc

 

[Jaymom]

2 Meter Jpole Page

The only part of it that i'm concerned about right now is the distance of 1.8 inches between the 2 vertical elements. It doesn't seem like enough distance. I noticed that this distance doesn't change between 144.000 and 149.000.

I will be using this antenna on 146.610 MHZ. Tomorrow morning mine is going to get a face lift.

Harold

 

[74IN]

not so good in the 4th dimension.

So time is a problem?