CB install in Expedition

[niemern]

I don't do e-mail. Feel free to share your questions here so others can benefit from the information.

New to this forum and really need your help, and completely value your opinion after reading hundreds of your posts... I am guessing you are a former "Coastie" radio man from your icon.
I have an aluminum body SUV (2018 Ford Expedition) and would like to install a CB radio. From you many posts, I understand that your recommendation is to use a center roof mounted NMO antenna like the Larsen NMO-27 or Laird equivalent.
My Ford dealer warns me that the ferrous metal of the NMO mount, or any ferrous metal mounting, will create corrosion with the aluminum body. Dissimilar metals create a galvanic couple and over time create corrosion. Besides, my wife would have a fit if I drilled a 3/4" hole in the roof of our SUV.
I am aware that there are alternatives, such as front hood/fender mounts, or the factory roof rack rails that are actually ferrous metal on my vehicle but not grounded to the chassis. When I put one lead of an ohm meter on the roof rail and the other to chassis ground, it shows open circuit or infinity. I could fashion a bracket on the roof rail with a steel plate and place a magnetic base for the Larsen antenna. I would just have to screw it on and remove it every time I went in or out of the garage. Not a convenient thing, but I would do it if this is the only viable option. Your prior posts however indicate this roof rail set up with the antenna few inches off the roof would not provide a good ground plane.
Regarding the fender/ hood options, I am told that for coil loaded antennas, either base or center loaded, the entire coil must be located above the roofline of the vehicle for good SWR and signal pattern. Hustler makes a center loaded, 3-foot antenna that would get the bottom of the coil just above the roof line.
All this aside, I do not understand RF ground plane theory, and am concerned after reading your posts that that the front mounted fender or hood lip mounts will not be ideal or provide reception beyond 1-2 miles max.
Any suggestions would be welcomed. Thanks very much in advance and thank you for your service.

 

[mmckenna]

New to this forum and really need your help, and completely value your opinion after reading hundreds of your posts... I am guessing you are a former "Coastie" radio man from your icon.
I have an aluminum body SUV (2018 Ford Expedition) and would like to install a CB radio. From you many posts, I understand that your recommendation is to use a center roof mounted NMO antenna like the Larsen NMO-27 or Laird equivalent.
My Ford dealer warns me that the ferrous metal of the NMO mount, or any ferrous metal mounting, will create corrosion with the aluminum body. Dissimilar metals create a galvanic couple and over time create corrosion.

That corrosion would require moisture. The NMO mounts are sealed so water isn't an issue. Plus, the mounts are not steel, they are usually brass or stainless.

Ambulance/fire truck bodies have been aluminum for decades. Installing an NMO mount on aluminum is not an issue.

Besides, my wife would have a fit if I drilled a 3/4" hole in the roof of our SUV.

My wife is 5'1". She'd never know. But seriously, don't piss her off.
Fortunately mine understands and has a ham ticket, so she had no problem with me installing an antenna on top of her Chevy Colorado when it was about 2 days old.

I am aware that there are alternatives, such as front hood/fender mounts, or the factory roof rack rails that are actually ferrous metal on my vehicle but not grounded to the chassis. When I put one lead of an ohm meter on the roof rail and the other to chassis ground, it shows open circuit or infinity. I could fashion a bracket on the roof rail with a steel plate and place a magnetic base for the Larsen antenna. I would just have to screw it on and remove it every time I went in or out of the garage. Not a convenient thing, but I would do it if this is the only viable option. Your prior posts however indicate this roof rail set up with the antenna few inches off the roof would not provide a good ground plane.

Right, you want the antenna down on the ground plane, not hovering above it.

Regarding the fender/ hood options, I am told that for coil loaded antennas, either base or center loaded, the entire coil must be located above the roofline of the vehicle for good SWR and signal pattern. Hustler makes a center loaded, 3-foot antenna that would get the bottom of the coil just above the roof line.

The base coil does not radiate much energy, the whip does that.

All this aside, I do not understand RF ground plane theory, and am concerned after reading your posts that that the front mounted fender or hood lip mounts will not be ideal or provide reception beyond 1-2 miles max.

No, it's not ideal, but it'll work as long as your expectations are set correctly. If you want maximum range from your radio, you really want to pay attention to the antenna installation. It's the radios interface to the outside world, and you want it to work well.

Since it sounds like you don't want to do the mount on the roof, then you have to accept the drawbacks.

But 1-2 miles probably won't be a big deal. If that's the mount that works for your application and wife, then that's what you've got to do.

I'd still go with the Larsen NMO-27 on that mount. Good antenna that will outlast your vehicle, and probably you'll pass the antenna down to your grandkids.

Any suggestions would be welcomed. Thanks very much in advance and thank you for your service.

Happy to help.

 

[Hans13]

I gain knowledge from just about every one of your posts, mmckenna. Thanks.

 

[mmckenna]

I gain knowledge from just about every one of your posts, mmckenna. Thanks.

Thanks. I'm still learning myself, so take what I saw with a bit of salt.

 

[AK9R]

All the NMO mounts I've seen are either made of brass or stainless steel. Granted, some installations may require a bracket to attach the NMO mount to the body and that bracket may be plain steel.

That said, Ford has published a Special Vehicle Engineering bulletin, attached, that discusses how to attach accessories to aluminum body panels. The bulletin gives some recommendations for ways to protect against galvanic corrosion.