J-pole antenna question

[Scoutdad57]

I'm trying to demystify the witchcraft that is a j-pole antenna. Where the feed line comes into the SO-239 bulkhead connector, the frame of the connector is connected to the shield of the coax - which is grounded. That metal frame is also connected ( soldered ) to one element of the antenna, and then the center conductor of the coax is soldered to another part of the copper tubing just a few inches away from the connector. Why is this not a short circuit across the output of the radio?  I know I'm missing something - I just don't know what.

[Lscott]

5 hours ago, Scoutdad57 said:

I'm trying to demystify the witchcraft that is a j-pole antenna. Where the feed line comes into the SO-239 bulkhead connector, the frame of the connector is connected to the shield of the coax - which is grounded. That metal frame is also connected ( soldered ) to one element of the antenna, and then the center conductor of the coax is soldered to another part of the copper tubing just a few inches away from the connector. Why is this not a short circuit across the output of the radio?  I know I'm missing something - I just don't know what.

https://www.wikiwand.com/en/J-pole_antenna

[SteveShannon]

5 hours ago, Scoutdad57 said:

I'm trying to demystify the witchcraft that is a j-pole antenna. Where the feed line comes into the SO-239 bulkhead connector, the frame of the connector is connected to the shield of the coax - which is grounded. That metal frame is also connected ( soldered ) to one element of the antenna, and then the center conductor of the coax is soldered to another part of the copper tubing just a few inches away from the connector. Why is this not a short circuit across the output of the radio?  I know I'm missing something - I just don't know what.

It is a short circuit for DC, but this is ultra high frequency AC where you have waveforms and reactive impedance. 
Here’s a pretty good explanation:

 

[marcspaz]

@Sshannon love Dave.  He's got some good videos.

[SteveShannon]

50 minutes ago, marcspaz said:

@Sshannon love Dave.  He's got some good videos.

I liked his videos better before he started trying to make one each day, but fortunately this video was from before then. 
I liked Stan Gibilisco’s videos too. I’m sorry he passed away. He has a good one about how J-poles work also. 
Unfortunately I lose focus trying to watch Ed Fong explain the same antenna. 

It looks like if you straighten out the J it looks just like an off center fed dipole with a delta match. 
Here’s Stan’s video:

 

[axorlov]

Dave Casler touched on important point, the common mode current, which J-pole antennas are very susceptible to. But on UHF frequencies this cute (rather ugly) loop of coax is not going to stop your common mode current at all. Better, expensive chokes are needed with UHF J-poles. This is the reason why Ed Fong antennas do not work when mounted on metal masts.