VHF/UHF Antennas - Front Bumper Mounts

[offroad_nomad]

Have any of you guys mounted your antennas on your front bumper? I'm thinking of mounting my VHF antenna on my TJM bumper with a clamp-on TJM Aerial Bracket
http://us.st11.yimg.com/store1.yimg.com/I/cruiserconnection_1889_18540710
and a NMO mount. I'm trying to find anyone that has done something similar or uses some sort of a front bumper mount. Thanks.

[asteffes]

This is a slight tangent, but what is the reason for mounting an antenna to the bumper? I've found it distracting when riding in vehicles with an antenna mounted in this manner. Is it to make it easier to remove the antenna when travelling through low-hanging brush? If that's the case, why not use a rubber duck on the roof instead?

[pskhaat]

I have UHF/VHF antenna on my ARB only for convenience as I'm too chicken to drill a proper hole in the roof. Bumper mounts are last resort IMO as except for maybe HF, provide a very poor groundplane for counterpoise.

I estimate a loss of 50% in performance by mounting my antenna at the ARB bar vs. trunk mounted on my commuter car.

[asteffes]

Why not use a magmount on the roof?

[offroad_nomad]

When not in use, my 4Runner is kept in our garage with my wife's car in the driveway. So I thought for convenience, I'd put the antenna with a NMO mount on the front bumper. When it can time to garage the truck, I could unscrew the antenna, screw on the NMO rain cap and drive into the garage.

Currently my CB antenna with a quick-disconnect resides on the passenger side of my front bumper. I don't even notice it now.

I'm not adverse to having an antenna on my roof with a mag mount. There isn't much available space on my roof, but I could be wrong. If you click on the link in my sig you'll see I have a roof rack, then a sun roof opening. With the rack and sunroof, where would be a good location to stick the mag mount? Thanks.

[Mlachica]

how about a little 12-14" antenna, is that too tall?

[UncleChris]

The main problem with a bumper mount is that you will have decreased performance of the antenna.

I have a Diamond K400 on my RAV4 that does a pretty good job without having to drill a hole through the roof. It clamps onto the rear door, and since it is close to the back, it is very easy to detach. It will work on doors and other places. It also has the ability to fold over with the loosening of a wingnut.

The principal problem you will experience with the bumper mount is a distinct lack of a ground plane. If you do a mount to the front bumper, take either a heavy gauge wire or coax shielding and ground the antenna mount to the vehicle ground in the engine compartment. That is supposed to improve the SWR a bit and in theory, give you a better ground plane.

[UncleChris]

how about a little 12-14" antenna, is that too tall?

I am running a comet rubber ducky(SBB-1) for wheeling. Since I am lazy, I have put off putting my normal antenna back on. The rubber ducky actually has pretty good performance and is pretty resilient. The Comet site http://www.cometantenna.com/products.php?CatID=1&famID=4&childID=4 has a picture of its flexibility.

It is a very good option for a rooftop.

[offroad_nomad]

Does the location of the roof make a difference? For optimal performance, does the antenna have to be in the center of the roof or can it be mounted towards one of the sides, up front or back? Thanks.

[asteffes]

The more surface area of metal under the antenna, the better a ground plane it will have. However, some is better than none, so don't sweat it if it's off-center.

[Mlachica]

I am running a comet rubber ducky(SBB-1) for wheeling. Since I am lazy, I have put off putting my normal antenna back on. The rubber ducky actually has pretty good performance and is pretty resilient. The Comet site http://www.cometantenna.com/products.php?CatID=1&famID=4&childID=4 has a picture of its flexibility.

It is a very good option for a rooftop.

I have a diamond nr-72bnmo 14" 2m/440 antenna (http://www.universal-radio.com/catalog/hamantm/1578.html). It's performance is outstanding and got really good reviews, I just can't remember the website that reviews all the ham eqpt. :confused:

[asteffes]

http://www.eham.net has a lot of useful reviews.

[asteffes]

I have a diamond nr-72bnmo 14" 2m/440 antenna (http://www.universal-radio.com/catalog/hamantm/1578.html). It's performance is outstanding and got really good reviews, I just can't remember the website that reviews all the ham eqpt. :confused:

I have that same antenna and would agree it's a good option.

[offroad_nomad]

Thanks again.

I'll need to check out the specs on that antenna to see if it Tx/Rx on 136-174 MHz.

[k6uk]

People often make the mistake of thinking that bumpers - especially metal ones - will provide an excellent ground plane. But unless they are welded to the frame - or properly grounded with copper strap, most bumpers are somewhat isolated from vehicle ground. Paint does act as an insolator.

So first of all we should all properly ground our metal bumpers - whether or not we are mounting antenna on them. This will increase our working ground plane, and improve performance of the antenna. Acutally while we are at it we should ground all the doors and body panels to the frame if possible. This is especially vital for HF Radios.

Now the other thing that affects our radiation pattern is where the antenna is located. Obviously the best location would be center of the roof - but often that just doesn't work out. But the closer you get the better - you will lose performance the lower you mount the antenna. But bumpers do often work well as a mount point.

One final note about bumper mounts. If you are running significant power, keep in mind that you can easily be exposing yourself to a lot of EMF radiation by positioning your antenna low. Yes the danger is real, so don't run a ton of power if you mount your antenna low. If you mount on the roof you are shielded much more effectively.

Okay... well thats all I got. Thought I would chime in.

73,

-Mike
K6UK

[offroad_nomad]

Mike,
Thanks for the input. I hadn't considered the EMF radiation from the antenna.

I think I found my set up:

A NMO mag roof mount and a Genesis VHF Wideband Unity model antenna (132-174 MHz), 18 3/4", "End Fed 1/4 Wave" from Antenex. (http://www.antenex.com/c_search.asp?txtFunction=browse2&selFamily=GEN&txtSubFamily=VHF+WIDEBAND+UNITY+MODEL)

I just need to find out if I can add a spring to the antenna because I will be encountering low limbs and branches on some trails.

[AndrewP]

Regarding antennas, you might want to focus on the electrical characteristics. A friend got me to see the light on this. I'm not sure you'll be happy with a 1/4 wave antenna. A 5/8 wave will have improved gain. The Wilson Mag mount as I posted elsewhere is a 5/8 wave mag mount with decent gain. It's trail tested too by me and cheap.

I can see some logic to having a shorter antenna, and will demo out one of thse flexy rubber 1/4 waves at some point.

From what I have read, the worst place to put the antenna is on the bumper for the reasons listed here. A good lip mount will be more secure than a mag mount and you might want to consider that as you upgrade. I have one ready to install, but I'll take my mag mount along to Moab in case I damage my main antenna.

I'm virtually certain the spring idea is out. It isn't CB! The steel whip in a mag mount though, is pretty tough.

KI6CXS

[offroad_nomad]

Thanks Andrew,
I went with a Genesis 3dB, 49 1/2", Base Load 5/8 wave antenna and a roof mag mount. I also picked up an external antenna to connect to my Uniden scanner out of curiosity to see if I get better reception.

[DaveInDenver]

The best antenna is a 1/4 wavelength whip in the middle of your roof. There is no argument on that. Other good spots are flat spots, like trunks or even hoods (isolating from ignition noise is a problem there, though).

But, that is not always practical. I personally have about 8 inches between my roof and garage door header. I put my antennas on my ARB upright and get fine performance. My pattern is obviously heavily biased towards the back, but it works pretty well in that direction. Think about this, lots of motorcyclists use antennas on their bikes, which have very little chance of large flat metal places. Sometimes they use cargo boxes with sheets of metal, but still that is not great. So figure out the antennas they use and they are typically pretty decent for bumper mounts.

My mount is a 4" piece of aluminum that is held onto the round tube with clamps. That aluminum is grounded to my bumper with a piece of braid. The bumper itself is then grounded to the frame with 2 pieces of grounding braid (never rely on the bolts, the anti-seize and powdercoat pretty much eliminate any chance of conductivity). I also ran a heavy braid from the battery to the frame, along with ground straps from the hood to firewall and front fenders. I run a Comet Challenger C-767 dual band, which is a 1/2 wavelength center loaded on 2m. It is not an elevated feedpoint 1/2 wavelength (which is completely ground plane non-dependent), but it seems to be less reliant on the counterpoise none-the-less.

My point is this, a bumper mount can be acceptable, but you have to take the steps to ground everything in the front and still you are going to give up range (especially to the front). By grounding I mean RF, too, not just electrically (they are different). The compromise for me was OK. I had a roof mount CB antenna for a while, but it got to be a pain taking the whip off to park and it got knocked off a lot while on the trail. A hard mount would have helped that, but still it gets whacked a lot and that's not good for the whip either. So I decided to use the bumper and did all I could to make it work. I personally like having the 2 whips on the corners of the front of the bumper. I bump into less stuff when I park my truck now, they act like markers for me. FWIW, on 2m at 50W, I typically get around 45 miles range in mixed terrain with decent strength (enough to open a repeater and still be understandable, although not necessarily super clear). To the front I get around 30 miles with open terrain or good position, maybe 25 or so in mixed terrain. For me, the compromise is worth it, but I'm not a super ham hobbyist, just another way to communicate.

[k6uk]

Good points on grounding, and the importance of minding the details when it comes to antenna installation. Thanks.


The best antenna is a 1/4 wavelength whip in the middle of your roof.

I'm not so sure I would agree - yes a central placement is the best placement, but 5/8s wave gives much better gain. But then, it is a lot longer of an antenna.



-Mike
K6UK

[offroad_nomad]

Dave,
If you get a chance, would you mind posting some pics of your bumper mount and the different grounding methods you describe? Thanks.

[DaveInDenver]

I'm not so sure I would agree - yes a central placement is the best placement, but 5/8s wave gives much better gain. But then, it is a lot longer of an antenna.


You are correct, there are ups and down when comparing 1/4 to 5/8. Keep in mind that antenna gain is not actual power gain, but really a focusing of energy when you compare your antenna to a 1/2 wavelength dipole.

The 5/8 antenna mounted straight up from your roof will get marginally longer range in the horizontal plane, but does slightly worse in the vertical. The 1/4 wavelength will have equally as much energy above you as in front or behind you. In open terrain you give up some with a 1/4, but that might be better if you are in a deep canyon and the other station is above you. In application on a flopping around truck whip it's probably not a big deal, as opposed to building a good mount, ground and feed.

[cruiser guy]

Just to revive an old thread. I recently bought an Icom 706 multiband radio for my travels. This radio has two antenna feeds, one for HF and one for 2 meter and 70 cm.
I was going to use a mag mount on the roof for the 2 meter/70 cm antenna for the good ground plane and a bumper mount on the front for the HF.
My truck is a diesel so there is no ignition noise to be concerned with (I will NEVER be getting a gasser so that's no ever going to be an issue).
Is there an issue using the HF antenna on the front bumper? The bumper is a winch type bumper and has a relatively large horizontal surface, probably 12" or more from the front of the truck.
Any suggestions on the antennas to use? I plan on using an antenna tuner for the HF antenna. I assume that the radio can deal with the 2 meter/70 cm antenna without a tuner but correct me if I'm wrong.

[gary in ohio]

Why not put a mount on the safari rack. There are a number of flip down antennas. that way you get the height VHF/UHF needs and the head room for the garage.