Melowave antenna on Front Bumper mounting location ? is there a benefit?

[Chris0275]

 

See a lot of images coming out of Australia and in the overlanding community here where folks are mounting large Melowave antennas to their front bumper for GMRS radios, is there some benefit to mounting there? Some of us with jeeps do not have the option to roof mount, and I'v read that the rear bumper or tire rack is not a ideal location either.  

Second question for the people who know, how high above the roof line is ideal when mounting a cowl level?  I have read that as long as an inch or so goes above the roof line that will work too, thanks for the input and look forward to reading your responses.

[WRWE456]

Welcome!

 

A good analogy of how antennas radiate energy in the form of a radio signal is that of a light bulb. Imagine a light bulb in the center of a empty dark room. The energy(light) goes out in all directions, now imagine that light bulb mounted in the different mounting locations on the jeep. If the light is below any part of the jeep body it creates a shadow that blocks the light. And just like light the closer an object is to the light the larger the shadow it makes than if it is further away, so the rear bumper location puts the antenna closer to the body which makes a larger shadow that the front bumper location that has it further away from the roof structure and makes a narrower shadow. As you can then imagine the roof is the best location as no shadow is created. (It also allows for a good ground plane on a metal roof anyway). This is a simplified explanation but should help you visualize what is happening.

Hope this helps.

[tweiss3]

There was a thread where the jeep owner mounted the antenna over the spare tire on a plate. Personally, I would prefer a 1/2 wave in a similar location (perhaps the base could be nearer the roof line) over the front bumper mounts. 

My understanding is that the AUS version of CB is UHF, and I can't explain why they all mount in that location other than "it's always how we did it". Keeping the coax out of the engine bay and away from other electronics, and putting the antenna as high as possible, with as much ground plane as possible would be my priorities. 

[Chris0275]

1 hour ago, WRWE456 said:

Welcome!

 

A good analogy of how antennas radiate energy in the form of a radio signal is that of a light bulb. Imagine a light bulb in the center of a empty dark room. The energy(light) goes out in all directions, now imagine that light bulb mounted in the different mounting locations on the jeep. If the light is below any part of the jeep body it creates a shadow that blocks the light. And just like light the closer an object is to the light the larger the shadow it makes than if it is further away, so the rear bumper location puts the antenna closer to the body which makes a larger shadow that the front bumper location that has it further away from the roof structure and makes a narrower shadow. As you can then imagine the roof is the best location as no shadow is created. (It also allows for a good ground plane on a metal roof anyway). This is a simplified explanation but should help you visualize what is happening.

Hope this helps.

Thank you for the reply, is the "light" emitted from the tip of the antenna or the middle?  I guess what I'm asking is if some of the top of the antenna protrudes beyond the roof line, would I be getting that all around "light" or would I still be losing some coverage for the parts of the antenna that do not extend above the roofline? Thanks again!

[tweiss3]

Just now, Chris0275 said:

Thank you for the reply, is the "light" emitted from the tip of the antenna or the middle?  I guess what I'm asking is if some of the top of the antenna protrudes beyond the roof line, would I be getting that all around "light" or would I still be losing some coverage for the parts of the antenna that do not extend above the roofline? Thanks again!

It is emitted along the entire radiating element. Look at the average location, which would be the middle. Ideally you want the base as close to meeting the elevation of the roof line, then you won't get any shadowing from the body of the truck.

 

FYI, when modeling antennas for range over topography, you use the base of the antenna, if that gives you any indication on how important it is to get the entire antenna above the car body.

[WRWE456]

What tweiss3 said.

[WRWE456]

A better analogy than a light bulb would be a fluorescent tube type light mounted vertically in place of the antenna.

[Chris0275]

1 hour ago, WRWE456 said:

A better analogy than a light bulb would be a fluorescent tube type light mounted vertically in place of the antenna.

Thanks for the response, makes sense, so in the case of a jeep with no top, how can I achieve the best results possible without mounting "above" the roof?

[WRXB215]

@Chris0275 Keep in mind that the ground plane doesn't have to be very big. If I recall, 6" diameter is enough for GMRS.