How much gain is lost putting the Antenna on the front bumper vs. attached to my roof rack? (1 Viewer)

[Fisher23]

I'v got a weBoost antenna, one of those broom stick ones from down under.

It's about 2.5' x 1" diameter and on a spring.

I'm thinking of mounting it on my front ARB bumper, vs the roof rack, mainly because some times I go in garages, and have not found a fold down mount. Unless I use one of those boat marine ones.

What are the fold down options?

How much gain would be lost the bumper mounting it, vs the roof mount?

Signal is important as I'm near the edge of the grid many times.

 

[WB8LBZ]

I'll take a stab at this, for the ARB bumper, I have the ARB Catchers Mask bumper on the front of my FJ40. I have found the offroad light brackets made by Rugged Ridge to be usable for antenna mounts (I got these 4 Wheel Parts).

This is for the common communications type antenna thread mounts.

I found a few fold down mounts at the DX Engineering store under fold down antenna mounts.

As far as the difference in coverage between the brush guard and the roof rack, much has been written in the ham radio world. The coverage is skewed usually toward the vehicle but its frequency dependent for lower frequencies. For cell phone frequencies, you might be pleasantly surprised - try it.

Larry in El Paso

 

[1969FJ]

As with ant antenna, the radiated energy has a pattern based on type. If it was roof mounted, center, the pattern would be free to radiate as expected. If you low mount it, the same energy would be blocked by where and how you mount it because of the vehicle obstruction.

 

[wapitimud]

I used to have a diagram of a car top, showing the relative gain losses in dB for a groundplane-type mobile whip. I forget those figures, but if mounting a 5/8 or 1/2 wave VHF/UHF antenna, the best place for it is near roof centre, significantly so.

If mounting a cellular antenna these gains may not be as great. A CB or amateur HF antenna may not physically fit well on roof centre without damaging something while offroading, and may need to go elsewhere on the vehicle.

 

[Kofoed]

All antennae benefit from being as high as possible. Think of your antenna as a flourescent tube light on end. Mount on bumper, go to rear of vehicle and see how much light is blocked by vehicle.

 

[LongDuck]

Relevant link from a recent article I wrote on this topic: HAMsters: The Case for 1/4 Wave Vertical Antennas for Off-Road Comms.

I'm having excellent signal reports from 1/2w mounted via mag mount to the flat plate on the right front section of my Slee Shortbus. It's not permanent, never comes loose, and is below the height of the truck for garage access. In short, a good setup won't lose much.

 

[wapitimud]

Magmounts are for a temporary setup. For a 1/2 wave and 1/4 you can survive without the bonded ground plane that you need for 5/8.

Your clear contacts into a local repeater aren't a thorough enough analysis.

Often the scuffs and scraping damage from the magnet can cause more damage than a proper hole or fixed mount ever would have.

I've never seen any public-safety vehicles with magmounts, maybe volunteer firefighters or something.

 

[Fisher23]

I'm using the front ARB antenna mounts and 2 of the above rugged ridge mounts suggested by @WB8LBZ for now.

I'm my jeep and pickup I could drill the roof, but with the 200 and the curtain airbags and whatever else is already in that attic I didn't want to drill it.

 

[Pskhaat]

Not a whole lot to add other than I've mounted numerous antennas on my bullbar throughout my Ham years with no discernible RX/TX problems whatsoever. Sure, drilling in the roof is the best, but I enter garages, and drive through tree'd areas; I use the larger diameter, big spring radome antennas and they fit perfectly on the bar.

 

[Fisher23]

Not a whole lot to add other than I've mounted numerous antennas on my bullbar throughout my Ham years with no discernible RX/TX problems whatsoever. Sure, drilling in the roof is the best, but I enter garages, and drive through tree'd areas; I use the larger diameter, big spring radome antennas and they fit perfectly on the bar.

I'm using the same antenna just a little shorter, it's bout 2.5 feet. Ended up mounting it to the roof rack with the above rugged ridge mount, which can easily fold down to a 90 for clearance.

 

[Skidoo]

Pattern changes with location of mount. Mounted in center of roof, the pattern is more or less centered, as mount location moves the pattern shifts. This shows pattern for a CB antenna, 2 Meter and Cell are higher frequency and may be a little different but will see similar effects.

 

[Fisher23]

Pattern changes with location of mount. Mounted in center of roof, the pattern is more or less centered, as mount location moves the pattern shifts. This shows pattern for a CB antenna, 2 Meter and Cell are higher frequency and may be a little different but will see similar effects.

View attachment 2391946

How do you interpret those ?

Example why would it reach out father with a corner mount vs a center roof mount if that is what it means. Doesn't make any sense to me.

 

[Skidoo]

Here is a quick explanation, as antenna theory can seem like magic most of the time. On a vehicle, the vehicle is the ground plane for the antenna. The antenna and ground plane make up the antenna system and the location of the ground plane effects the directionality of the the system. Taking an extreme case if you put a parabolic dish ground plane behind the antenna it will greatly extend the range in one direction. It does this by focusing all the antenna's energy in one direction. So shifting the antenna around the vehicle (ground plane) has some focusing effect on the antenna system. Also notice that the area inside the pattern is about the same. Note that if you are mostly talking to people behind and in front of you some of these mount locations are not very good.

 

[Fisher23]

Here is a quick explanation, as antenna theory can seem like magic most of the time. On a vehicle, the vehicle is the ground plane for the antenna. The antenna and ground plane make up the antenna system and the location of the ground plane effects the directionality of the the system. Taking an extreme case if you put a parabolic dish ground plane behind the antenna it will greatly extend the range in one direction. It does this by focusing all the antenna's energy in one direction. So shifting the antenna around the vehicle (ground plane) has some focusing effect on the antenna system. Also notice that the area inside the pattern is about the same. Note that if you are mostly talking to people behind and in front of you some of these mount locations are not very good.

So you are saying : If the antenna is mounted on the front bumper you would be able to talk with radios behind you better that radios in front of you; and the signal would travel farther behind you than if you had it mount in the center of the roof... correct?

 

[Skidoo]

In general yes. However an SUV is somewhat different than the car used in graphs above, also that was a CB antenna which are longer than Ham or Cell.
If the antenna you are using doesn't or barely sticks above the roof line, then instead of the ground plane enhancing in that direction it could be bouncing it back.
The shorter the antenna and if not mounted top center, the pattern can get weirder. For a taller antenna looking down the ground plane looks like a simple rectangle, as the antenna gets shorter that ground plane starts looking more complex depending on mounting location.

 

[Pskhaat]

So you are saying : If the antenna is mounted on the front bumper you would be able to talk with radios behind you better that radios in front of you; and the signal would travel farther behind you than if you had it mount in the center of the roof... correct?

FWIW, I had BETTER performance with a UHF radome antenna on my ARB bumper that I did with an NMO whip on the center of the roof. Same radio. There are sooooo many factors though, all I can offer is my anecdote.

 

[Fisher23]

Thanks !

 

[1MOA]

FWIW, I had BETTER performance with a UHF radome antenna on my ARB bumper that I did with an NMO whip on the center of the roof. Same radio. There are sooooo many factors though, all I can offer is my anecdote.

The bumper becomes a giant ground plane for the antenna.
I get better rx and TX properties with far less noise with a 1/4 wave mag mount antenna on a rack back mounted on my chevy truck on 2m than I do with a 45ft ground loop antenna at home.