"Rear corner of my Truck"... Explain...
Above the tail iights??? or Just behind the cab?
In my installation a 2002 GMC 2500HD Duramax Diesel extended cab., The Control head is in the over head console. No sunshine washes out the display there.? The transceiver main unit is mounted under the drivers seat. With a "BOSS 2" screwdriver tuner. The antenna is a Hi-Q 4 inch unit with a 10 inch mast to a cloverleaf capacity hat that uses 3 36" stainless steel 0.1 rods form the cloverleaf, using set screws with the center a 1" aluminum Hex cut from Hex Bar. and threaded with 3/8 thread straight thru. My whip above that is from a discarded HAMSTICK.? This is mounted to a "Headache Rack" just behind the cab on the truck bed. I designed the mount using 1.5" x 1/4 aluminum attached to the headache rack,? and a hing then 1.5x 3 plexiglass plate with a hole where the base of the Hi-Q is mounted.
At the top of the head ache rack. I have a black PVC 1" pipe cut to fit over the uprights on the headache rack. it is tywrapped to the Hi-Q mast just below the Coil assembly. It braces the antenna in the upright position. The base of the Hi-Q is 3-4 inches above the pickup bed top rail and 7-8 inches away from the drivers side rear of the cab. There is a 2:1 ferrite core unun under the plexiglass in a box to better match it to 25 ohms. as the feed point of the antenna is NOT 50 ohms.?
Now the Hi-Q coil is totally above the roof line by 2-3 inches. Then the 1 foot 3/8 rod to the clover leaf capacity hat and then the 4 foot SS top from a ham stick. It is below 13 feet 6 inches so traveling highways is not a problem and mounted on the drivers side it is in the center of the road not by the trees on the side of the road.
Now for parking garages, oil changes or? such times I need to "lower" the antenna? I just pull up on the Black PVC brace and lay the entire antenna down in the bed with about 2 feet of the top whip protruding from the tailgate. Takes 5 seconds to fold down or raise the antenna.
The top of the headache rack I have 3 more NMO mounts for various antenna's and a LED emergency light for SKYWARN type adventures.
I also run a 3/4" braided strap the 4 coaxes and power for the lights, between the bed and cab. I cut a 2" hole in the back of the cab just above the floor and placed a PVC bushing there so wires will not chafe.? So everything is grounded. I might add the top of the headache rack I added a piano hing and a aluminum plate that the NMO type antenna's and the LED emergency light can "tip into the bed, So if I want to carry, a ladder or pipe, I can place it on top without crushing an antenna or light..? I was fortunate to get the headache rack? at an exceptional price because the manufacturer is 30 miles away in Winfield, Kansas.
I installed this about 10-12 years ago. I bought the truck new. It arrived at the dealer on 9/10/2001 and I told them I'd pick it up the next day. the next day was 9/11.. For reasons I will not go into now I am keeping the truck "forever"? I have to reinstall everything because it's in the bump shop- a hit and run and I am having a total repaint job. It should be ready 3-4 days as soon a bumper arrives made of unobtainium.?
Personally I have no chokes in use, I do know the pickup bed is only held on by 4 bolts as we removed my bed to fix the typical bottom rear cab rust all GM pickups have.
I believe you have a grounding problem. You may even have to ground the exhaust pipe..? I would invest in a nanovna and start checking impedance's... You did not mention if you use a unun. Your Hi-Q is not a 50 ohm feed point till It gets to about 20 meters..
Years ago UnUN at the feed point was covered extensively at the Hi-Q web site before it changed hands.? the 2:1 unun I use lowers 50 ohms to right around 23 ohms. Works great on 80-40m mobile. .
I can see you having this type of problem going between a unibody car and a pickup with a frame.
Chrysler user manual says no 2way radios over 3 watts... GM -- call the GM Tech center in Warren, Michigan they have all kinds of info on installing 2 way radio's..?
Larry W8LM
ARRL Life Member- Licensed 57 years 11 months.
Larry Macionski