A truck bed is plenty large enough for a ground plane at 27MHz allowing the antenna to achieve a good match. My last truck was a Tundra with 6 1/2ft bed and I had an 80-10m HF screwdriver mounted about a foot behind the cab and down low on the inner bed wall. The cab was not a problem at all and being on the inside bed wall gave me all four vertical surfaces of the bed wall and the bed itself as a ground plane.
One important test for an HF antenna on the lower bands like 40 and 80m is the feed point impedance. A large screwdriver antenna or any antenna using lots of coil for loading runs in the 12-15 ohm range on 40m and lower on 80m like 10-12 ohms IF it has an adequate ground plane. My screwdriver antenna came in right on target mounted to the bed wall behind the cab and if you were to move it to say the trailer hitch or some other spot with poor ground plane the impedance would be up in the 40-50 ohm range on 40 and 80m meaning huge resistive loss. On 10m and CB the big loading coil is bypassed on the screwdriver and it acts just like a 9ft whip with 10m and CB working really well with that setup giving an easy 50 ohm match.
I just finished an install on a new truck with a very small bed, a Jeep Gladiator and the bed is only about 5 1/2 ft long and narrower than my Tundra. I mounted a fixture about 2/3 of the way back from the cab and high on the inner bed wall as a universal antenna mount for everything and testing it with various CB antennas from 4ft to 9ft worked great. All the whips matched perfect and had very wide band width plus the screwdriver antenna came in on target again with really low impedance on 40 and 80m meaning the ground plane is way more than adequate and I did this just in the last week. This is with a bed that seems to be floating from everything and I did not ground or bond the bed to anything because it works great as is.
Since RF currents flowing on the sheet metal around the antenna are going to be on the same side of the sheet metal as the antenna, grounding the underneath of the bed to something like the frame or battery will accomplish nothing, unless your trying to improve the DC ground back to the battery for some lighting project. RF will not have a clue that ground is there, its only concerned with the sheet metal that's immediately around the antenna on the same side as the antenna.
So before you condemn the stake pocket mount run a few tests to see what the problem actually is before shotgunning a bunch of stuff that will probably not fix anything. First try bending the whip away from the cab with some insulated string while watching the SWR meter to rule out the cab proximity to the whip. I suspect there will be little or no change. Do you have the braid of the coax grounded to the sheet metal right at the feed point? Some Firestick cable assys have a floating ground for their no ground plane antenna and those coax assys are trouble on all but a few installs. Try attaching 9ft of wire to the ground side of the mount and stretch it across the bed as a ground radial. If the antenna matches up fine then there probably is insufficient ground plane. If so is the top of the bed rail where the stake pocket is located bonded to the inner walls and bed?
My last two installs were to the upper inside bed wall and I have not recently done an install on the very top of the bed rail, so that's an unknown for me right now. But I do know if you put a mount on the inner bed wall an inch below the top of the bed rail and a good foot back from the cab it will match fine and work well. I've mounted dozens and dozens of them there over the years without any problems for people running everything from 2ft to 9ft whips.
One important test for an HF antenna on the lower bands like 40 and 80m is the feed point impedance. A large screwdriver antenna or any antenna using lots of coil for loading runs in the 12-15 ohm range on 40m and lower on 80m like 10-12 ohms IF it has an adequate ground plane. My screwdriver antenna came in right on target mounted to the bed wall behind the cab and if you were to move it to say the trailer hitch or some other spot with poor ground plane the impedance would be up in the 40-50 ohm range on 40 and 80m meaning huge resistive loss. On 10m and CB the big loading coil is bypassed on the screwdriver and it acts just like a 9ft whip with 10m and CB working really well with that setup giving an easy 50 ohm match.
I just finished an install on a new truck with a very small bed, a Jeep Gladiator and the bed is only about 5 1/2 ft long and narrower than my Tundra. I mounted a fixture about 2/3 of the way back from the cab and high on the inner bed wall as a universal antenna mount for everything and testing it with various CB antennas from 4ft to 9ft worked great. All the whips matched perfect and had very wide band width plus the screwdriver antenna came in on target again with really low impedance on 40 and 80m meaning the ground plane is way more than adequate and I did this just in the last week. This is with a bed that seems to be floating from everything and I did not ground or bond the bed to anything because it works great as is.
Since RF currents flowing on the sheet metal around the antenna are going to be on the same side of the sheet metal as the antenna, grounding the underneath of the bed to something like the frame or battery will accomplish nothing, unless your trying to improve the DC ground back to the battery for some lighting project. RF will not have a clue that ground is there, its only concerned with the sheet metal that's immediately around the antenna on the same side as the antenna.
So before you condemn the stake pocket mount run a few tests to see what the problem actually is before shotgunning a bunch of stuff that will probably not fix anything. First try bending the whip away from the cab with some insulated string while watching the SWR meter to rule out the cab proximity to the whip. I suspect there will be little or no change. Do you have the braid of the coax grounded to the sheet metal right at the feed point? Some Firestick cable assys have a floating ground for their no ground plane antenna and those coax assys are trouble on all but a few installs. Try attaching 9ft of wire to the ground side of the mount and stretch it across the bed as a ground radial. If the antenna matches up fine then there probably is insufficient ground plane. If so is the top of the bed rail where the stake pocket is located bonded to the inner walls and bed?
My last two installs were to the upper inside bed wall and I have not recently done an install on the very top of the bed rail, so that's an unknown for me right now. But I do know if you put a mount on the inner bed wall an inch below the top of the bed rail and a good foot back from the cab it will match fine and work well. I've mounted dozens and dozens of them there over the years without any problems for people running everything from 2ft to 9ft whips.
