Mobile Antenna / Rooftop Rack Compatability?

[Eltee]

I have a rooftop antenna mount on my SUV. If I sometimes attach my rooftop cargo rack can I have the antenna poke up between the bars without problems?

My rack is similar to the one on my truck seen here.

[PACNWComms]

Metal roof racks will impact antennas, both electrically and physically. How much depends on the antenna, placement and construction of both the antenna and the roof rack. However, with some vehicles, such as aluminum skinned Ford F-150's, steel roof racks often help, increasing the ground plane for the antenna. However, real world.....unless you are trying to get the perfect signal out of your radio/antenna/vehicle combination, most people will not notice the impact of a roof rack. For UHF and GMRS, I would not worry about it too much. As for RF exposure, I try to meet the FCC guidance, keeping several feet between UHF antennas and people inside the vehicle.

For that truck/SUV, putting an antenna near the back of that roof rack, or on the roof rack, above the rear light would be the most useful and least impacted by the roof rack. This also places the antenna at a high point, extending range. But, depending on length, may be an issue in garages and decked parking lots.

[Eltee]

2 hours ago, PACNWComms said:

"... As for RF exposure, I try to meet the FCC guidance, keeping several feet between UHF antennas and people inside the vehicle."

 

Uh oh ... having spent nearly 30 years in police cars with low band, high band, UHF, trunking, T-Band, etc. radio antennas right over my head or on the trunk lid may explain my behavior!  

[BoxCar]

50W ERP is 6 feet of clearance in free space. There are several calculators for the new guidelines available on the net. ARRL has one that's fairly easy to use as an example. But as far as shielding goes, an aluminum ground plane is as good as steel. Aluminum converts magnetic energy to eddy currents within the metal so the RF is effectively neutralized.

[PACNWComms]

+1 on the aluminum part. In a previous life, I worked around ionizing radiation, and many knee jerk into thinking that lead is the only shielding that works. Borated concrete and aluminum work well for ionizing radiation. Aluminum skinned aircraft and spacecraft work just fine, even with RF equipment on board, and with each radiating around each other, if it is engineered to work together.

RF radiation wise, my biggest job was where a fleet of ships had been retrofitted with Icom IC-M602 VHF marine radios, and a few IC-M608 VHF/HF combination radios. These are plastic cased radios with rear aluminum cooling fins, and very little RF shielding. They do not work well together on the bridge of a ship, even if spread twenty feet apart or more. They were intended for pleasure craft, where only one radio was needed.

Fast forward to me delving back into FRS/GMRS territory, and I am relieved to see many GMRS radios built with full metal enclosures, such as the GM-30 handheld and DB20-G mobile radios. Connected to a good antenna, coax, and appropriate connectors, an aluminum roof rack is going to work just fine. You will most likely have to worry more about physical damage should you place items in the rack.

Be sure to let everyone know how it works out for your particular installation.