Cascadia dipole?

You only need one of those metal brackets. The one with 3 holes. You need a plastic insulator between it and the 40 inch extension. You also need another insulator between the head of the bolt and the 3 hole bracket. Take a close up pic excluding antenna elements so we can see how it is bolted together.

 

We need to see a picture taken at this angle to see the plastic insulators in the proper places.

 

Yes i know i need one,just showing the original and the one i had made..
I thought just the ant sending the signal needed to be isolated but the grounding ant had to be grounded to bracket...
Anyways i didnt get to far with it cause i was tryin to tune the ground element and it doesnt wanna come down much...Its a 5 ft fs and im sure i pulled off a foot of wire and plastic and even had to cut down the fibreglass to keep the red rubber cover on it..According to my rig expert the ant im tryin to tune 1st(grounding ant)the ant tunes its best at the mid 24500 ish to 25700ish freq....Kinda stumped on that...

Anyways,to cold and dark now and im on the road in the morn so i just put my 10k back for now to get me by till im home again next week..

 

If you pull that much wire off of that antenna its total garbage and unusable at this point. Time to start over with another one. As long as that flat metal plate is isolated from the extension it should be easy to make something work you just gotta make sure that bolt that holds it on to the extension does not touch the metal plate itself and has a plastic insulator to keep it separated. The ground antenna can be bolted directly to the metal plate

 

@craig_sez
Typically, you would want to tune both top and bottom radiators at the same time, because a dipole is a balanced antenna, and both elements are radiators.
Since you have a 5ftr on top, and a 4ftr on bottom, it wont be balanced, you can try tuneing the top to match the bottom, and see where you are.

However, I see a couple things that may not be working in your favor.
Ive experimented with a few wire dipoles, in different configurations for my base setup, but never mobile. So take this fwiw.

2 things.. dipoles dont like anything conductive in the near radiation field. And.. the angle at which the coax enters the feed point can have an effect on your system. These 2 reasons alone, are what have discouraged me from trying a mobile dipole. But I know, some have 'made' them work.
Imo, mounting a dipole to that 40" mast, is going to have a huge negative effect on your system. It is in the near radiation field.
Routing your coax parallel to the bottom radiator is also not a good idea. Your asking for all kinds of issues to arise there.

If you're going to continue with your dipole project, I would suggest winding an air choke at the feedpoint, 4-5 turns of coax, about 4" in diameter. Or place some snap on ferrite beads on the coax, at the feed point. Either will help prevent cmc, which imo, is going to be your biggest hurdle with a mobile dipole.

Just my .02 to maybe help save some hairs from being pulled. I hope you get it figured out.

 

Actually i was given the idea by rabbi..Not sure if i was thinkin along the 40" dipole anyways or not..
Well without spending a few hundred maken a bracket so i can mount (again rabbi's idea but i already had something close)a pair of dipoles(out in the wind stteam) out in the back of the cab im empty of ideas..
Tried 4/5/7 footers on a single mirror arm mount and i couldnt even tune, unless it had something to do with the ss mount itself..
Only thing that works this far is my 10k on the 40" tall mount..

 

i keep saying that but in a different way, there is introducing of common mode currents and I suggested that they use a BALUN to go from the unbalanced coax to the balanced antenna but it get ignore. I also pointed out there has to be a gap between the radiator and the reflector because these are not dipoles but rather colinear antennas with their own ground and interacts with the ground itself.

 

So bottom line in basic lingo,its not worth the effort for someone who doesnt know ant theory and how to fix the wrongs??????

 

Mounting your 10k on that 40" mast is killing the effeciency of your system, and raising the angle of radiation. It may tune, but an AA cannot see the losses introduced into your system with your mounting location. It is stated throughout k0bg's site, to never mount a mobile on such a mast, the g-p must start at the feed point for max effeciency.

I would work more with the 7ft whip jmo.

 

I havent given the gap of the two radiators any thought, but you are probably right. With my wire dipoles, I would just space them a couple inches apart, and never considered the affect.