Antenna section and placement

[caryt]

I would like to find a Antenna that will work with my TM-V71A that I could mount on my camper which is Aluminum and has Aluminum rails.
I'm unsure if I mount it to one of the rails if being over the skin of the roof 1.5" +- will be a issue. Also next to the Solar panels?
I'd like to keep the Antenna height under 24" if possible. Placement of the Antenna ?
Jeeps tops are fiberglass so no use as a ground plane. I could mount on the hood lip but would prefer not to unless no choice.

Thanks

 

[mmckenna]

The antenna is going to work better with a ground plane directly under it. Hovering above on a rail is not going to work as well.

I'd recommend installing a permanent NMO mount on top of the alu-cab, in front of the solar panel. That'll make the best use of the available ground plane, and get the antenna up and in the clear.

As for the antenna itself, I ran the Larsen NMO-2/70SH for years and never had an issue with it. Passed it down to my brother in law who ran it for years. Very durable antenna that will work well with that radio and has a spring base that will be handy if it finds a low branch.

Larsen NMO2/70SH Premium Larsen 2m/70cm Amateur Ham Radio Antenna Short Dual Band

Larsen NMO2/70SH Premium Larsen 2m/70cm Amateur Ham Radio Antenna Short Dual Band

theantennafarm.com

There are other options if you need them, but that's what I'd recommend.

 

[caryt]

Thanks, just how large of a ground plane will it require?
I don't want to penetrate the camper as I would also have to exit it and enter the Jeep cab.
If I added a front rack and full covered the top of it with Aluminum giving a area of 20x52 would that work well?

Thanks

 

[mmckenna]

Thanks, just how large of a ground plane will it require?

An ideal ground plane would be at least 1/4 wavelength in all directions under the antenna on your lowest operating frequency.
For the amateur radio 2 meter band, that would be 19.5 inches.
That's why I recommended putting it on the alu cab.

I don't want to penetrate the camper as I would also have to exit it and enter the Jeep cab.
If I added a front rack and full covered the top of it with Aluminum giving a area of 20x52 would that work well?

It would work. No, not "perfect", but that's not going to be a big deal, people do it all the time. In fact, the overlanding crowd seem to be perfectly content with compromised antenna mounts, especially when performance isn't the main goal.

What you want to do is get the antenna mounted directly on the ground plane. Mounting it above it isn't the same and will impact performance. Mounting it on the edge of that rack would not be ideal as it raises it, and also offsets it on the ground plane. Having the antenna offset like that is going to make it directional to some extent.

But, welcome to the challenging world of how to mount an antenna on a Jeep.


You need to decide for yourself how important this antenna is and go from there. A compromised mount is not ideal, but it's better than nothing.

 

[vagrant]

I use a Diamond NR770 1/2 wave antenna. It’s 38” long. Instead of putting it on a lower hood mount, I use a Diamond motorized lift. This allows me to park in my garage. The motorized lift is mounted to a roof rail. Twice I neglected to lower it. Fortunately, it is made to allow the antenna to lower when striking something and keep working after a quick reset. I have used that motorized mount for over 10 years. There are also manual mounts with a thumb screw for easy up/down use.

Alternatively, there is the Compactenna. That antenna thrives with lack of a ground plane. I think it is only 7 or 9 inches. Easy to use a mount with that on the aluminum rail.

 

[bharvey2]

I use a Diamond NR770 1/2 wave antenna. It’s 38” long. Instead of putting it on a lower hood mount, I use a Diamond motorized lift. This allows me to park in my garage. The motorized lift is mounted to a roof rail. Twice I neglected to lower it. Fortunately, it is made to allow the antenna to lower when striking something and keep working after a quick reset. I have used that motorized mount for over 10 years. There are also manual mounts with a thumb screw for easy up/down use.

Alternatively, there is the Compactenna. That antenna thrives with lack of a ground plane. I think it is only 7 or 9 inches. Easy to use a mount with that on the aluminum rail.

I have the same antenna in a home-made stake pocket mount in my F150. (It is paired with a Kenwood TM-V71A) While it isn't the best solution, it performs surprisingly well given the shortcomings. I even bought a spare many years ago but have yet to put it to used. Are they still available?

 

[vagrant]

@bharvey2 - They are available in black and chrome and have a built-in fold-over as well. While they work without a ground plane, they will perform better and favor the direction of metal underneath. I use a second one mounted on the lower back corner of my SUV tailgate. It works well for APRS.

 

[bharvey2]

@bharvey2 - They are available in black and chrome and have a built-in fold-over as well. While they work without a ground plane, they will perform better and favor the direction of metal underneath. I use a second one mounted on the lower back corner of my SUV tailgate. It works well for APRS.

Good to know. When I purchased my first one, I was specifically looking to get something closer to 1/2 wave because of the lack of a ground plane in a stake pocket mount. There weren't many that fit the bill. I've also have a clamp on mount (ergo, poor groundplane) that I've used on a few occasions (for temp mounting) and this one can get me by without too much of a fight. If someone has there heart set on (or is limited to) a sub-optimal mounting setup, this is what I'd recommend.