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Mobile antennas and high gain = not always best?


WSAK691

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I can’t remember if I read about it somewhere here in these forums or on a FB group post, but someone was mentioning about, for example, a 6db gain mobile antenna. The way that it accomplishes that gain is by shallowing down that take off angle into something more narrow of disc shaped and really concentrating that radiation to something like a degree or two. And that’s great for ERP increases, but a mound of solid dirt in front of you at the foot of an incline on the roadway is just going to absorb it if you’re running 5 watts or 50. And in this scenario, you’re just beaming that signal nearly horizontally right into it. So if there was a receiving vehicle a mile ahead and already on top of that increased elevation, he may not hear anything at all. 
 

But now suppose you have a 3bd gain antenna which is a bit more Omni direction in the vertical axis, perhaps shooting as high as 10-15 degrees. It’s lower ERP, but would be casting signal into more useful directions in realistic terrain environments. 
 

When you first get into mobile line of sight radio-ing, one of the first things that you become more keen on is how the terrain lays out ahead of you as you’re driving. You see those high points, and low dips and you just know when you’re optimal for shooting out a nice signal and when you’re likely to get into a dead spot down in a hole. So with that being said, is a high gain vertical actually counter productive in mobile applications?

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A quarter wave antenna pattern looks much like a round ball. A gain antenna pattern takes more the shape of a football, or even an exaggerated football (ellipse). 

I've never gone wrong performance wise with a 1/4 wave... in UHF, VHF, 800... 

Nothing against the gainers, they have their place.

Just an observation, but usually I see HAM radio (I am a HAM too) using gain antennae because we try to do the most with the least power. Commercial and GMRS largely used fixed power (even though there are adjustable power GMRS radios now) and many times have more power than they really need, so any marginal effect of a higher gain antenna is not seen or even known. That's an opinion, don't anyone get sideways.  

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 The general idea with higher gain is to concentrate the radiated energy into the horizontal plane so as to not waste as much by sending it into space or into the ground like an omni does. It's more of a directional design. If you are in a wide open terrain like in a desert or on a hill with a wide view of the surrounding area this can be an advantage. However if you are in hilly terrain where you contacts may be at different elevations or when off roading where vehicles may be climbing steep angles and tilting the antenna sharply it doesn't work so well. Besides if off roading with a group you are usually not as far apart so the extra reach is not needed. In those cases an omni is better.

 Thinking of how lights work is a good analogy. A bare light bulb will illuminate a wide area but not very brightly but a spot light concentrates the energy in one general direction with great intensity. It will reach farther in the dark. Antennas work much the same way.

 

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I use a 9dB gain antenna for 2m and 70cm for the range. While there are a few hills and valleys around me, there is also a lot of fairly flat open farm ground too. A 5 or 6 dB antenna normally is better for areas with lots of hills/mountains and forests.

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