Lesson learned

Yup. Antennas mounted at the midline of the vehicle will have a much more even radiation pattern than one mounted on the mirror. Easier to deal with than a cophased antenna system as well.

 

Co-phased antennas are by nature directional because signals that arrive at both antennas at the same time
(broadside or forward and backward if the antennas are mounted on the mirrors) are added together
and signals that arrive at different times/angles are not added because the peaks arrive at different times
If they arrive far enough out of phase/time they subtract and cancel each other out.
At ~18 feet apart (for CB freuencies) the signals that arrive from side to side cancel out and leave a deep null




even at 104 inch separation directionality is evident



The more metal the ground plane has toward the direction in question the higher the gain in that direction.
So for co-phased antennas to counteract the long ground plane of a truck and trailer (and thereby improve omnidirectional gain )they would have to be mounted front and back as side to side mounting would magnify the ground planes lack of symmetry.

I will agree the return seems to small to bother with co-phasing (on a mobile) I never did.

 

YEARS AGO ...

I cophased 2 1/4 wave wips on 52.525 mhz it never worked out and I went back to a lone wip on the trunk.
If you go look up the instruction manual for a Hygain 12avq about page 12 has instructions on co-phasing them with diagrams ect ...

http://www.thiecom.de/pdf/AV-12AVQ.pdf

 

Nice find. Their patterns and results look a lot like the ones I got from modeling. I considered including out of phase feeding in my post but opted for shorter is better.

I'll have to dissect the "Figure 4 360 Cardioid Arrangement" I have 20+ models of the "super scanner" fed various ways.