Mobile GMRS Antenna Question

[WRUE915]

While I understand 1/4 and 5/8 wave antennas require ground plane. 1/2 wave does not (although it still helps).

 

I currently use a mag mounted 5/8 wave antenna. But both wanting a more permanent solution, and the fact that I often have a cargo box on the roof is forcing me to look at other options.

 

If I am going to place the radio somewhere with no solid ground plane such as the rear corner of my hood near the winshield (on a lip or dotch light bracket)... would I still benefit from a 5/8 over 1/2? Or would the lack of good ground plane make the 5/8 perform worse than a 1/2 wave in this situation?

[Lscott]

11 hours ago, WRUE915 said:

 

While I understand 1/4 and 5/8 wave antennas require ground plane. 1/2 wave does not (although it still helps).

 

I currently use a mag mounted 5/8 wave antenna. But both wanting a more permanent solution, and the fact that I often have a cargo box on the roof is forcing me to look at other options.

 

If I am going to place the radio somewhere with no solid ground plane such as the rear corner of my hood near the winshield (on a lip or dotch light bracket)... would I still benefit from a 5/8 over 1/2? Or would the lack of good ground plane make the 5/8 perform worse than a 1/2 wave in this situation?

 

I would go with the 1/2 wave simply because you'll have more flexibility where to mount it. The small additional gain you get from a 5/8 wave along with the complication of needing a good plane, IMHO isn't worth it. Myself I got a new vehicle and I'm going to install a 1/2 wave since I don't want to drill holes or deal with a magnet mount to use a 5/8 wave antenna.

[WRUE915]

I would go with the 1/2 wave simply because you'll have more flexibility where to mount it. The small additional gain you get from a 5/8 wave along with the complication of needing a good plane, IMHO isn't worth it. Myself I got a new vehicle and I'm going to install a 1/2 wave since I don't want to drill holes or deal with a magnet mount to use a 5/8 wave antenna.

Thanks. That's my thought exactly.

My question is this then... with NO ground plane on any of the antenna, will the 1/2 wave outperform a 1/4 or 5/8?

From my understanding the answer would be yes. But I can find a solid answer.

Sorry, this is more of an antenna theory question vs practical application. My plan is to get a 1/2 for my purposes. But this question came up with others and I didn't know exactly how to answer it.

[Lscott]

3 minutes ago, WRUE915 said:

Thanks. That's my thought exactly.

My question is this then... with NO ground plane on any of the antenna, will the 1/2 wave outperform a 1/4 or 5/8?

From my understanding the answer would be yes. But I can find a solid answer.

Sorry, this is more of an antenna theory question vs practical application. My plan is to get a 1/2 for my purposes. But this question came up with others and I didn't know exactly how to answer it.

You should have about the same "gain" using a 1/4 wave with a ground plane compared to a 1/2 wave without one. The difference is the 1/2 wave will be a taller antenna, about double that of a 1/4 wave naturally.

Unless you have a large ground plane for a 5/8 wave antenna they aren't worth the hassle.

https://www.w8ji.com/VHF mobile vertical.htm

[MichaelLAX]

44 minutes ago, WRUE915 said:

My question is this then... with NO ground plane on any of the antenna, will the 1/2 wave outperform a 1/4 or 5/8?

I try to stay away from antenna theory questions, but if all else is equal and no ground planes, then 5/8 will give you the best propagation, certainly for an HT (I know not your situation).

I used to carry with me a telescoping 2 meter 5/8 for those times that I needed an extra ummph to make it into a repeater, and with my HT my body acted as the ground plane.

Needless to say, for 2 meters, 5/8 is quite a length!

[Lscott]

35 minutes ago, MichaelLAX said:

I try to stay away from antenna theory questions, but if all else is equal and no ground planes, then 5/8 will give you the best propagation,

A 5/8 wave requires a ground plane.

[MichaelLAX]

10 minutes ago, Lscott said:

A 5/8 wave requires a ground plane.

What was his question? How did I answer it?

Another reason I stay away from antenna theory questions...

[Lscott]

2 hours ago, MichaelLAX said:

Another reason I stay away from antenna theory questions...

Maybe.

[WRQC527]

In my experience, if you try to run a 1/4 wave, or especially a 5/8 wave antenna without a ground plane, the SWR is quite high, which at best will kill your signal, and at worst is not good for the radio. There is no real difference in performance between a 1/4 wave and a 1/2 wave if the 1/4 wave has a decent ground plane. In reality, a 1/4 wave without a decent ground plane will "underperform" a 1/2 wave. The 5/8 wave should outperform both the 1/4 and 1/2 wave antennas if it has a good ground plane because it has more gain. Antenna theory is voodoo science at its best.

[JWSmith]

This is a mobile application. With that in mind, the metal of the vehicle is the ground plane. I use a 5/8 wave 2 meter antenna mounted on my headache rack on my truck. Also, I've run a ground strap down and attached to the frame. My opinion is that a 5/8 wave antenna is a great way to go. Just remember that for best omni-directional performance, the antenna should be placed near the center of the vehicle. I will be doing the same for my GMRS antenna.

73 de WRVQ648 / KC1KLA