Anyone tried a co-phased dipole?

Setup:

2012 Volvo highrise sleeper
twin K-40 5' adjustable fiberglass
Belden 75ohm RG-58
Cobra 29, Magnum S-680
SWR @ 1:1.3
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Background:

Just for comparison...I've ran many years out talking my ears in a day cab Mack pulling flat bed, w/ single antenna mounted center on headache rack. Didn't matter if I ran barefoot with a steel roof infront, aluminum trailer behind 1:1 swr was AWESOME! 10-15miles easy at night.

Now I've been fighting with new Volvo, pulling dry van for past year. The factory coax had to go, and mounted a single K40 off passenger mirror, talked good out front but couldn't hear well, moved to driver's mirror hears better but transmission really suffers. So I grabbed another matching K40 and co-phased thinking I'd focus signal front and rear...not so much!
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Fix:

I believe the obvious problem is lack of a good ground plane. BTW yes I did run ground wire to the mirror mounts. My first idea would be to add small aluminum plates below the antenna for better RF reflection, however I think it would need to be too large to make a difference? Then it was suggested that I add a grounded small rubber ducky antenna below my K40's in effect making it a vertical dipole.
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Question:

• Has anyone attempted this with good results?
• Was it worth the time and cost?
• Any other suggestions are welcome!

Thanks for any help!

 

My mistake, it is RG 59 75 ohm. thx Easy Money..

Unless I hear otherwise from someone who has tried, I will likely start with only one... then for chits and giggles add the other side.

 

Update:
I had some issues with engine noise that needed to be dealt with first, and seems I have eliminated most of it. Surprisingly I found most of it was through the antennas and a slight tilt forward, 1 o'clock position works best (not road tested yet). Because these were decent K40's I didn't feel it was needed previously since they are stiff in the wind. This also decreased my SWR to 1:1.0... BONUS!

I bent "U" brackets and used the antenna mount as a template for holes to attach to the antenna brackets. Drilled oversized center to fit the pl259 upper and correct size on under side. Because the mirror arms are oversized like many newer trucks I had to purchase longer bolts to fit correctly and 4 extra to level it beneath the bracket. A bolt to attach the antenna adapter, and used the original 24" fiberglass whips that came stock on the truck, and it was complete. Checked for good grounds, and rechecked SWR...to my surprise no change which either means the stock antennas are perfect, or I have accomplished nothing, meaning it was not a ground plan issue at all.

Removed the SWR meter, and turned the radio on... and could hear no background noise, only skips on top of skips... thats a good thing! A few radio checks and seems good. Won't be able to test the distance difference till I get out of this valley and motor down the road tonight.

 

It was a long progression of disappointment! And I forget in what order? But ultimately all the work and expense was for nothing more than a lesson learned. The Volvo already had enough metal in the cab that made the dipole useless, or at least unmeasurable. My biggest problem was the static noise while driving and I didn't cure that till after all the effort... If only I had cured that first. But afterwards I was only running a single fibreglass off the driver side mirror, which did a fine job.

Funny I'm reading this today, just got home from cleaning that truck out and tossed some of those old fittings and co-phase coax away. They put me into a brand new Cascadia, LOL. Doesn't even have a place to mount CB from factory.