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For two meters, a 5/8th wave antenna has the best omni gain.

But I think the lobe is very low takeoff and not good for mountain work.

What is best for the mountains on a mobile?

Yes, I know not much is going to get over mountains at 144Mhz and above but I want to know what will work best?

•For repeaters on mountains

•And for simplex to other vehicles in repeater "dead zones"

Terrain at 39.501419 , -106.15162650000002

Time for the Constraints

•The antenna has to magnetically mount to the roof of a vehicle, which is a van. I have a very strong Tri-magnet mount. (unless someone can think of a different way without manipulation of the vehicle in any way).

•The antenna can not take up much horizontal space due to bicycles on the roof nearby.

•By much I mean nothing more than a 10cm by 10cm block horizontally at the base and up to the height of a bicycle.

•The antenna can not be taller than the street regulations for traffic lights, power lines, etc (obviously)

•Weight does not matter

•The antenna should not pop off the roof

•I want to optimize for best signal strength to other stations.

•Power I will be running - 50 watts

•Band- Primarily VHF, but maybe a bit of UHF. Optimize for high performance in VHF.

•Max speed of vehicle will be 60 Mph on a highway stretch, so wind strain should be taken in consideration, but not importance (as long as the antenna doesn't fall off).

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  • $\begingroup$ "best"? Like, it should be light, but it should be strong? It should be small, but it should be directional? It should be directional, but I also shouldn't need to aim it? It should be long, but it should have a low wind load? There are literally dozens of trade-offs involved in this decision, and "mountains" doesn't even begin to provide a basis to decide. $\endgroup$ Commented Dec 22, 2014 at 13:41
  • $\begingroup$ I added a few constraints. Is that better $\endgroup$ Commented Dec 22, 2014 at 15:32
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    $\begingroup$ Maybe, but it sounds like the answer is still a whip, which you've excluded. I think to solve your problem, it would be much more productive and useful to ask about aspects of any particular antenna you don't understand, then make your own decision. $\endgroup$ Commented Dec 22, 2014 at 15:34

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If very high angle coverage is important to you, go for a 1/4 wave monopole antenna, mounted in the middle of the roof. A magnetic mount should be fine.

A 5/8 wave vertical antenna has more gain than a a 1/4 wave vertical only up to an elevation of about 15 degrees, and drops away quickly above 25 degrees. There's a diagram here.

The bicycles on the roof will not help at all. Having a 10cm x 10cm clear area around the antenna isn't enough. You need to keep an upright bicycle at least 1 m away to avoid major interference with patterns. Can you move the antenna elsewhere on the vehicle? If you must use the radio and the bicycles, you could extend the antenna through the bicycles on a pole. If you do this, it must then be a "ground independent" antenna, something with radials that stick out the sides. The pole won't be an acceptable ground plane by itself.

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    $\begingroup$ The images you link are for an antenna on an ideal, infinite ground plane. A car roof is far from that. Here's a more realistic simulation from this article. $\endgroup$ Commented Dec 24, 2014 at 14:42
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I'd suggest a good 1/2 wave antenna. You lose a bit of gain relative to a 5/8, but you'll have a good bit more than a 1/4. Also, 1/2s don't need a groundplane, while 1/4s do.

If you get one with traps in it (most do) it will work nicely on 70cm in addition to 2m. At ~1m long, you shouldn't have any trouble clearing traffic lights, wires, and even most parking structures. You also shouldn't have any trouble with a larger single-mag mount. I used to have my 5/8 on a single-mag on the trunk of my Camry and it could handle 70mph road speeds plus wind with no issues.

BTW, A 5/8 is just a 1/2 with that extra 1/8 added to intentionally shape the beam closer to the horizon as most people don't usually care to hit stations that much higher in elevation.

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