Two-way radio antenna mounting?

[KJ1H]

I am trying to figure out some mounting options for an amateur radio antenna on my 2003 Dodge conversion van. With a high-top roof, the typical hole through the roof trick won't work because fiberglass is not an electrical conductor, so a poor ground connection. I'd consider a rain gutter mount, or a mount that bolts onto the front fender under the hood, but I haven't been able to find a winning combination of mount and 144/440 MHz antenna to use. 

What are some other solutions people have used? While I'm specifically looking at ham radio, CB antenna advice is welcome as well, since mounts and hardware can be used for either. Thanks!

 

[tx2sturgis]

The simplest mount is a Larsen L mount, this picture shows it upside down, it actually mounts to the fender material up under the hood, you need about 1/4 inch of gap (between  the hood and fender) to mount this AND pass the coax thru.

https://www.gigaparts.com/larsen-tmb34b.html

If your hood has a steep angle, this bracket may not accommodate that, unless you modify it. It will handle most normal hoof angles.

This is an NMO mount and so you will also need the NMO coax assembly and a dual-band NMO mount 2m/440 antenna, I recommend the Comet SBB5, not real expensive, but rugged and long lasting. 

https://www.gigaparts.com/larsen-nmok.html

https://www.gigaparts.com/comet-antennas-sbb-5nmo.html

They have moderate gain, suitable for this type of installation. These antennas can last for years even on commercial trucks.

 

[tx2sturgis]

Missed the edit window...and since most vehicles don't have a 'hoof' angle, here is the correction of that typo:

"If your hood has a steep angle this bracket may not accommodate that, unless you modify it. It will handle most normal hood angles."

.

 

[speedhighway46]

Use a separate half-wave antenna for each band; no counterpoise is required.

 

[Boondock Saint]

You can run a separate ground wire along with your antenna and have a great ground source to the chassis. Just out both cables in some cheap loom.

 

[highdesertranger]

I have heard that was a poor substitute for a good good plane. so you are saying that it is just as good? or it works good enough? or is it barely passable?

now I heard if you add a piece of Sheetmetal under the antenna and bond the antenna to it and bond a known good ground to the sheetmetal it works just fine. I believe I even saw a formula to determine the size the sheetmetal needs to be.

highdesertranger

 

[tx2sturgis]

Yes, HDR, for VHF/UHF antennas up on a fiberglass topper or van's hightop surface, a 'ground wire' running to the frame does nothing, except waste a half hour of your time. That ground wire can sometimes create a good reading on a simple SWR meter, but the gain pattern and feedpoint impedance will generally be lousy.

A ground plane (sheet metal, screen, or several radials) of some kind is what is needed, near the feedpoint, to maintain the feedpoint impedance (VSWR) and the desired gain of the antenna. 

But, the reason I recommend (in this situation) the slightly less optimal cowl or fender mounting is to keep the antenna out of harms way when driving under tree branches, low underpasses, rest area canopies, etc. 

I've broken a few antennas over a period of decades, and broken antennas don't work well at all!

 

[highdesertranger]

thanks Texas. highdesertranger