Antenna location for Jeep Wrangler with roof rack

[grahamfitter]

Apologies if this has been asked and answered before but I couldn't find it!

I'm planning on getting a CB radio for my Jeep and I'm at a complete loss as to where best to mount an antenna...

View attachment 15233View attachment 15234

There seems to be a variety of possible locations: rack crossbars, rack mounts, tailgate, bumpers, front fenders and probably others I haven't thought of. Which would work best and what length antenna would be required?

Thanks in advance.

Cheers,
Graham

 

[Gear]

Well I have tried a couple of different spots.

The passenger side has a Firestick(CB) and the driver side has a Diamond(2M). Location was chosen so that I could freely move in and out of the garage. Reception was fine for close convoy communications with the CB. Not the best place but it worked great with the garage.

CB Passenger side 2M Driver side. On my JK I put them on top of the rack. I was told by the guys at Diamond Antenna that this would be the best location. Reception is good. But the garage keeps winning.(I just bent the Diamond antenna the other day)

I might try moving the antenna's down to the front light tabs. It would work for the garage. I am just not sure on having a 2M antenna that close to the passengers.

Well this probable did not help you a whole lot, but at least it gave you a bump to the top.

Any others have any advise.

 

[DaveInDenver]

I might try moving the antenna's down to the front light tabs. It would work for the garage. I am just not sure on having a 2M antenna that close to the passengers.

Well this probable did not help you a whole lot, but at least it gave you a bump to the top.

That's actually a very important comment! Transmitting with 50W on 2m produces a strong enough field that giving thought to your RF exposure is not a bad thing at all. Having the antenna that close to a passenger with the top off is enough that I'd personally stop and think about it first. A CB antenna would probably be OK, though.

 

[DaveInDenver]

I had the chance to do some quick calculations. Assuming relatively long exposure of 30 minutes, I believe the safe power density for people on VHF is considered 0.2 mW/cm^2. At 50W with a unity gain (1/4 wave) antenna that works out to a safe distance of around 8 feet. This would be considered the uncontrolled exposure by the FCC. If you assume a higher exposure is OK for shorter periods, say about 5 minutes time averaged, you can allow a higher exposure. I assumed 1.0 mW/cm^2. At those levels a safe distance is about 3.5 feet, which would be the controlled exposure by the FCC. If you have gain with your antenna, then the exposure changes in the gain aspect and would be higher (i.e you'd need more distance with a 1/2 or 5/8 wavelength antenna).

Hams should go here and read OET65 about RF exposure limits:
http://www.fcc.gov/oet/rfsafety/

A legal 4W CB (5W EIRP) operator probably doesn't need to be concerned, but can't hurt to read about it. Beyond a couple of feet a legal CB will be below all accepted exposure limits. By my scribbles a 5W EIRP antenna at 28MHz will produce a 0.2mW/cm^2 density at 0.8 feet and a 1.0 mW/cm^2 power density only at 2 feet.

Please don't take these numbers as gospel, they were done quickly over my oatmeal breakfast, but they're quick & dirty rules of thumb anyway.

 

[articulate]

For the sake of clearing the garage, I put the antenna low and used a 48" (I think). Here it's on a ball swivel mount (Hustler C-32):

Did you want to mount it on the rack?

 

[gary in ohio]

Mobile and portable ham radio are specifically excluded from the RF exposure rules. I am not saying you shouldnt be aware of them, just that your mobile station will never be checked.

 

[DaveInDenver]

Mobile and portable ham radio are specifically excluded from the RF exposure rules. I am not saying you shouldnt be aware of them, just that your mobile station will never be checked.

No station is exempt from NEPA MPE rules, and thus FCC rules. It is true that in general amateur stations are exempt from routine inspection for that compliance.

However, just because hams are not subject to FCC or EPA examination does not mean they can ignore the laws of EM physics and human physiology. Anytime you are operating in close proximity to the antenna and power levels are sufficient, you need to evaluate your RF exposure.

OET65, Supplement B addresses amateur radio more specifically:
http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65b.pdf

 

[articulate]

:xxrotflma

Dave and Gary must be running for President. You fellas sure know how to take a simple question and complicate the whole thing with information that hardly pertains.

 

[grahamfitter]

That's actually a very important comment! Transmitting with 50W on 2m produces a strong enough field that giving thought to your RF exposure is not a bad thing at all. Having the antenna that close to a passenger with the top off is enough that I'd personally stop and think about it first. A CB antenna would probably be OK, though.

For the sake of clearing the garage, I put the antenna low and used a 48" (I think). Here it's on a ball swivel mount (Hustler C-32):

...

Did you want to mount it on the rack?

I don't really care where the antenna goes as long as its not on the front bumper (which would drive me nuts) and doesn't irradiate me unnecessarily (which would damage my nuts.)

Originally I thought that the front drivers' side rack mount would be ideal because its accessible, requires minimal cabling and is out of sight to the driver. The rack would be fine too and I could easily find space on the foremost or rearmost crossbar which would be out of the way of the rest of the stuff that's up there. On the trail trees could be a problem here and there if a long antenna is located on high on the rack.

The question is really which location is going to give me the best performance for my 4 watts?

Cheers,
Graham

 

[DaveInDenver]

:xxrotflma

Dave and Gary must be running for President. You fellas sure know how to take a simple question and complicate the whole thing with information that hardly pertains.

Come on, it was more on topic than a lot of stuff. At least it was remotely about a good location. It was something I took into account when I put the antenna on the roof of my truck, having a good shield for my oh so culturally important noggin full of ideas and knowledge.

 

[Scenic WonderRunner]

:xxrotflma

Dave and Gary must be running for President. You fellas sure know how to take a simple question and complicate the whole thing with information that hardly pertains.

Ah shucks Mark..... give the guys a break.....they are just tryin' to stuff their Coffers! "So many Candidates for Mods......so little Dime". (posted all in fun! as in laughing around the campfire.)

I'm no antenna guru.

I did find this link interesting..........

It gives just enough info. to make you ask a ton of more questions! Which can be a good thing. Maybe you could even email the guy and ask some questions.

.

 

[ExpoMike]

Not that this could not be easily replicated, Walcott CB list this.

http://www.walcottcb.com/product_info.php?cPath=284_288&products_id=1033

 

[lysol]

Reviving from the dead. Where are people mounting their antennas nowadays with roofracks? I'm sure the reception is much better up there. How are you grounding the antennas that need grounded?

 

[binrat]

Reviving from the dead. Where are people mounting their antennas nowadays with roofracks? I'm sure the reception is much better up there. How are you grounding the antennas that need grounded?

Ensuring a constant good ground is the crux when mounting up high. I had a friend who thought having 3 antennas mounted on his headache rack "looked cool" but was a constant problem with grounding. I would recommend grounding straps that are as short as possible for the rack.

 

[lysol]

Ensuring a constant good ground is the crux when mounting up high. I had a friend who thought having 3 antennas mounted on his headache rack "looked cool" but was a constant problem with grounding. I would recommend grounding straps that are as short as possible for the rack.

Yea, I'm more worried about the rack being grounded properly. The whole top part should be good because it is completely welded as one but ensuring it's grounded to the frame is the hard part. Would probably have to grind down a few spots and add either a thick gauge wire (maybe on the 4 corners) or grounding straps to the frame.