Cascadia dipole?

You're lucky my new job is going to be requiring me to drive one of those trucks starting on the 22nd

 

I just took a closer look at that picture and that dipole is shorted out to the truck so it's really not a dipole anymore in that picture.
In order for that to be a dipole that bracket that bolts to the truck would have to be insulated electrically from the truck but those bolts shorted out directly to the body of the truck

 

You can't have an isolated element from the ground (rf and electrical) and call it a dipole. There is something else missing too, the distances between the elements.

 

They are electrically connected to each other and the truck rendering one of the elements useless

 

Hows that?

So the ground on a regular dipole will render one element useless too?

 

If the ground element is grounded to a metal object that's enormous it will no longer be resonant rendering itself useless

 

Not all the time.

The size of the ground is irrelevant in this case, because the feed line is unbalanced and the ground is fed right from the radio which is attached to the chassis ground. What can and often happens is the feed line acts as part of the antenna and the second element of the antenna system in a case of trying to isolate it feeds back along the feed line causing common mode currents acting as part of the antenna system. It may give a good SWR but the power radiating out of the antenna is attenuated somewhat.

If you ever used random wire or even tuned dipoles with just a coax, you can see what I'm getting at.

One thing I eluded to in another post, maybe this thread, I don't remember is the fact that there should be a gap between antenna segments more than a few inches in order for it to be an effective dipole. You guys have it so tight, that there is a problem with actual radiating of the signal in most cases. In truth, you are not even using a dipole but another type of antenna that needs that gap to work.

Another and more bizarre thing that I tried and it worked was to take the unbalanced feed line (coax) and used a Balun with the last few inches of feed line an open wire. It seemed to settle the problem with common mode currents in trucks. The Balun doesn't have to be huge as long as you don't saturate the core with too much power.

 

For future readers....
Ground element must not make electrical contact with body of truck..

 

Perhaps you could Enlighten us as to proper distances between the elements. Now that I think about it I wonder if increasing or decreasing the distance between the elements changes the feed Point impedance?