Ham Antenna Location

[Stryder106]

Hi All,

I just purchased my first ham radio (Yaesu FMT-400/XDR with a Diamond NR-770HB antenna). I have a question for you guys on antenna mounting. I fabbed a roof rack and made a tab for it and mounted it up there - the antenna has a hinge so I can lay it down if clearance is an issue, but it is really up there (just under 9' total height). We are pretty new to overlanding/expedition/adventure offroading and am certainly brand new to ham radios. As a result, I ask questions and look at what others who know more than I do are doing and try and determine if that's right for me or not (I don't know what I don't know - right?).
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With that said, I keep seeing advertisements, pics, articles, features, etc featuring overlanding vehicles (I THINK predominantly Australian - certainly the ARB and HEMA vehicles) with the antennae mounted on the front bumper bull bar - rather than on the rear or roof, or even fender. And the antennae seem to be much thicker. My questions are: 1) Is there a particular reason or benefit for mounting it directly in your field of vision? Or in that particular location? 2) Is this purely an Australian thing? 3) Am I doing something wrong mounting it up on my roof rack that high in the air? 4) Why are those antennae so much thicker? Did I buy the wrong thing?
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The research I did led me to believe that I should have the antenna up and free from being blocked by the vehicle (admittedly, I could be reading more of the requirement for a CB antenna into this). Sorry for the complete noob questions, but I just want to get it right - and thanks in advance for the replies and knowledge sharing.

 

[PhulesAU]

The antennas mounted there are usually for HF and don't block any view, but it does help to keep from breaking them off. the brands seen like that usually have a built in tuner at the base and are kind of impractical to mount else where. what you bought is probably fine ( without looking it up) but mounting it on a rack is not a real good choice, it will work but it could be a lot better.

 

[Stryder106]

Thanks for the info. This antenna is specifically designed for a rack rather than bigger ground plane. But, your point raises another question: How is a bulbar on a front bumper better than a roof rack (which is the same diameter steel)? I'm sure there's some science here that I'm not getting, but on the surface - it doesn't seem like there would be any advantage other than reduced overall height for mitigating damage - which seems to be a the disadvantage of reduced range.

 

[sonoronos]

aussie youtubers mount them on the bullbar because it looks cool. maybe because it's easier to keep track of the aerials.

from an rf perspective, higher is almost always better.

range, on the other hand, isn't everything.

 

[Hillbilly Heaven]

Excellent choice of VHF/UHF mounting location. Would like for you do yourself a favor. Please check to make sure the roof rack has a good ground back to vehicle chassis and that the mount you are using is grounded to the rack. With the many mounting points between the vehicle and antenna and their various paints and coatings there may not be a proper ground. For quick check with the radio off disconnect the antenna coax from the radio. With a multimeter measure the resistance between the outside of the coax connector, not the thimble, and a known good ground. It should be zero or very near it. If it is not check to make sure you have direct metal to metal contact at the mounting points bracket to rack and rack to vehicle.

 

[DaveInDenver]

Higher is always better and the roof is the best place RF-wise for a VHF/UHF antenna.

With an HF antenna it's less critical because the roof and indeed the whole car doesn't provide enough surface area to truly act as an efficient ground plane. For a CB or ham antenna for bands 10m and lower (down to 160m) putting the antenna on the bumpers or side sheet metal is fine and actually almost necessary due to their length. It's actually almost impossible to carry a mobile antenna of any sort that works with any efficiency below 40m anyway since the antenna length itself is prohibitive.

But as sonoronos mentions a vehicle antenna is a compromise and sometimes locating them in an perhaps non-ideal location from a radiation perspective is preferred or necessary. I've mentioned it before I think but you need to be able to live with your aerials so if drilling a hole in the middle of your roof is going to make our life difficult (such as driving into garages or under tree canopies) then doing a fender or bumper mount can be made to work well enough.

Can't say for sure why all the trucks down under have them on their bull bars other than to prevent them from being broken off. They do use rigid masts with spring bases more often than flexible whips, which would require a more solid mount than sheet metal. Doing a bracket on a roof rack would work, such as I believe you have done. Another possibility is interference with roof tents or luggage. Hard to say. I have my antennas at the base of my windshield but that's only because I haven't gotten around to dropping the headliner and installing NMO bases in my roof.

BTW, just a grammatical mention, insects have antennae (multiple biological sensory appendages) while amateur radio operators have antennas (multiple electromagnetic radiating devices).

 

[arz]

Mounted out on the vehicle corners, they will do double duty indicating the corner as well as their RF job.

Sent from my KFFOWI using Tapatalk

 

[Stryder106]

Thanks for all the info guys - much appreciated. AS for grounding - hmmm - I think I need to redo my roof rack - I mounted rubber between it and my roof to help with vibration and sealing - but per your info - think I took away the grounding by doing that - dang it.
Antenna, Antennas, and Antennae - LOL. I actually thought Antennae was the plural of antenna - oops - I just learned something - THANKS!!!
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Overall height of my ham antenna is just under 9' - but it is hinged so I can lay it down. I keep looking at it and am not quite sure how comfortable I am with it that high in the air because if I forget about it - it will take a hit. It is thin and flexible so hopefully it wouldn't break. My concern is if I get into something lower clearance that has me having to have it down for long periods of time, would I lose the ability to communicate?

 

[colodak]

I've attached a piece of steel to my roof rack and putting a mag mount 2M antenna up, easily removed

 

[DaveInDenver]

Thanks for all the info guys - much appreciated. AS for grounding - hmmm - I think I need to redo my roof rack - I mounted rubber between it and my roof to help with vibration and sealing - but per your info - think I took away the grounding by doing that - dang it.

You can use braided strap to connect it electrically to the truck. This is common with roof racks, swing-away tire mounts, bumpers and even making sure all the body panels themselves are bonded together.

 

[Stryder106]

THANK YOU BOTH!!!!!

 

[mep1811]

Higher is always better. I have my antenna on my roof rack so it is over seven feet high. My friend has his mounted on his fender. He is always out of range in short distances with ne and other truck with roof mounted antennas.

 

[BigSwede]

While roof center is the best location for radio performance, it is highly vulnerable to tree branches. If you are going to be mostly in the desert, maybe not a problem, but around here we are sometime literally plowing through overgrown trails that destroy a roof-mounted antenna in short order.

I have a half-wave antenna mounted on the bullbar, doesn't need much ground plane and survives the branches. I have conversed with other vehicles 15 or more miles away so it does the job for me.