Another J pole question

[Blue Jay]

Waiting on the big brown truck to drop off the radio I am building a copper J pole for 2 M, one thing I am not clear on is the mounting. Does one need to isolate it from DC ground? Pictures I have seen are hard to tell but most look like it would just screw to a piece of pipe for a mast but searching the forum last night one said it should be mounted to a piece of PVC pipe. Could someone help out this newbee?

TIA

 

[HiDef]

No it doesn't need to be isolated from DC ground. You should use a 1:1 Balun at the feed because it is a balanced load fed with unbalanced transmission line.

A coil of a turn or 2 of coax right downstream of the antenna connector would probably work fine for you.

 

[6 Meters Rules]

It Doesn't Matter Really, But I Isolate Mine From Ground Cause that's how My! Elmer Showed ME! & I Have tried Both Ways & I Can Talk Farther With it Isolated At least in Indiana I Have Worked the East Coast With Mine In A Band opening ! Several Times Like 8 -12 Times If I Can Help Let me Know!

 

[W5LZ]

Isolating a 'J'-pole from 'ground' isn't necessary. It's also not a 'balanced' antenna so no balun is required, and as described, that's a choke, not a balun. If you just want to isolate a 'J'-pole, it isn't going to hurt anything. Using a choke almost never hurts anything.
- 'Doc

 

[Blue Jay]

Thanks everyone, back to work and then hope for some warmer weather!

 

[Lazybones1222]

Isolating a 'J'-pole from 'ground' isn't necessary. It's also not a 'balanced' antenna so no balun is required, and as described, that's a choke, not a balun. If you just want to isolate a 'J'-pole, it isn't going to hurt anything. Using a choke almost never hurts anything.
- 'Doc

what he said - I use one mounted just like that and it works great.

 

[kd-5-bgt]

I made a j pole a while back and I used some rope and run thye rope through a tree limb up about 45 feet,the antenna works great ! I dont see myself buying another antenna for my 2 meter base set up

 

[bob85]

should you use a choke balun or not hmmmmm good question,
should we even call it a choke balun as cebik and other people do or a line isolator or a plain old choke,

cebik says we should always use a choke balun with a j because of the almost inevitable inballance of currents in the matching section/feedpoint ( which also causes some radiation from that section ), as such the potential for unwanted common mode currents on feedline are high,
the arrl also says use a choke balun,
some say isolate the antenna from the mast some say connecting the long leg of the j to a mast causes no problems,

i would use a ( choke balun/line isolator/choke ) at the feedpoint and isolate it from the mast then experiment with connecting it to the mast to see which works best for the design of jpole you decide to use,
if neither suite your needs start again with a different design, they all work, some work better than others.

 

[Marconi]

should you use a choke balun or not hmmmmm good question,
should we even call it a choke balun as cebik and other people do or a line isolator or a plain old choke,

cebik says we should always use a choke balun with a j because of the almost inevitable inballance of currents in the matching section/feedpoint ( which also causes some radiation from that section ), as such the potential for unwanted common mode currents on feedline are high,
the arrl also says use a choke balun,
some say isolate the antenna from the mast some say connecting the long leg of the j to a mast causes no problems,

i would use a ( choke balun/line isolator/choke ) at the feedpoint and isolate it from the mast then experiment with connecting it to the mast to see which works best for the design of jpole you decide to use,
if neither suite your needs start again with a different design, they all work, some work better than others.

Hey Bob you are saying, to try both---to physically isolate and then not isolate the choke from the mast? I think I have read someone like W8JI or Cebik talking about such, right?

Just to be clear, there has been a lot of discussion of late about isolating antennas too, you even mention this here in your post.

 

[HiDef]

Isolating a 'J'-pole from 'ground' isn't necessary. It's also not a 'balanced' antenna so no balun is required, and as described, that's a choke, not a balun. If you just want to isolate a 'J'-pole, it isn't going to hurt anything. Using a choke almost never hurts anything.
- 'Doc

A J-pole is simply a half wave end fed connected directly to a 1/4 wave matching stub. It might look like an unbalanced load but it isn't.

You are correct a choke balun isn't necessary. Who knows, you might work more folks besides the neighbors with that radiating feedline

 

[bob85]

eddie there is much conflicting information on the j-pole and indeed the whole isolation of antennas idea in general,
i looked at the j-pole while looking for answers to the sigma enigma, i would have to go through it again to make sure but i am pretty sure cebik talks about standard and none standard j-poles, he has much to say and one of those things is use a choke balun or whatever you choose to call it because you will almost definately have a slight inballance of currents at the feedpoint, the other is you may want to isolate the antenna from the mast,
when i made j-poles for 27mhz years back i used a choke made from coax, it used too much coax too many turns for 27mhz but i thought more was better back then, i have learened different since,
at the end of the day its up to the user to decide what works best for them,

i would always use a choke for the coax and try the mast isolated vs connected to the antenna and make up my own mind for the j-pole i was using.