Grounding antenna to roof rack

[ndamico]

So i have a 95 range rover with a full voyager roof rack. The rack is steel powdercoated and the roof is aluminum. I can't run an nmo mount as my rack covers the whole roof. I overland with it and need the folding mount when i offroad in the trees. I am using a diamond folding bar mount now which works well with my diamond sr770 antenna w/ uhf connector. Question is i think it can work better. On a trip last weekend we were talking simplex and i couldnt hear as far away as others in my group with similar rack-mounted antennas and mobile rigs. right now i have a piece of rubber isolating the mount from the rack. Will grinding paint off the rack and removing the isolation runber help anything? Btw my mobile rig is a kenwood d710g. I know in the center of the roof with nmo would be best but it wont work on this vehicle.

I have no tuner, etc but would buy one if it would help me.

Any advice?

 

[mmckenna]

Proper grounding always helps, even with "ground independent" antennas.

The trick is to not confuse a DC ground with an RF ground. They can be the same thing, but can also be different.

The ideal solution would be to make sure the antenna mount actually is the antenna ground. Check for continuity from the outer conductor of the coaxial connector on the radio end to the antenna mount body. There should be continuity. If there is, then you need to make sure the mount is properly grounded to your rack. Don't rely on the clamping force of the mount, as that can often get water into it, and that will lead to corrosion. Ideally you'd want to use a short length of copper braid. Use crimped and soldered lugs on each end. Connect one end to the antenna mounting base, preferably using stainless steel hardware, flat washers and lock washers/lock nut. Do the same thing on the rack. Drill a hole and use stainless steel hardware to make a good connection. Seal it up with a waterproof sealer after you've confirmed it all works. That should -probably- provide a good enough ground plane for a 2 meter/70 centimeter antenna. You could go farther by making sure the rack is grounded to the vehicle body in the same fashion as above. Might not be necessary, but it won't hurt.

Ideally you want these antennas in the center of the ground plane to prevent the radiation pattern going directional. Might not work with your set up, but try to avoid putting the antenna out at the edges of the vehicle.

You should not need a tuner. In reality tuners just hide the issues from the radio, they don't necessarily improve performance. You'd be better off investing in a good SWR meter and making sure your antenna is tuned correctly. An SWR meter is a much more versatile tool.

I've been running a 1/2 wave VHF antenna on my Polaris Ranger for a few years now, connected to a 25 watt Motorola CDM-750. I made sure the antenna mount was grounded to the roll cage.