Antenna advice with alum skin veh

[Motorradmark]

I am just getting into ham and am having some issue with a mobile antenna for the ht in my Land Rover 110. Alum skin on roof.
I have a fire stick for my cb mounted on antenna tab on front brush guard. I have 1/4 (144 MHz)/ 5/8wave @430MHz mag mount .but no steel to mount it, except the roof rack, which isn’t grounded or solid sheet, like a roof.

I don’t think I have any ground plane with the rack or alum roof. Not opposed to drilling another hole in the roof if it would work. Not height challenged , Just lack of steel, it seems.

Any recommendations or advice welcome.

 

[dreadlocks]

mount it to rack, run ground strap internally to the roof if they are isolated.. aluminum makes a fine ground plane and you dont have to be attached directly too it.. my antenna is mounted to an isolated aluminum rack over an aluminum roof, I didnt do anything else and it has great coverage.. try it first, then work from there.

 

[4x4JeepCamper]

Here's another idea. I have a 2017 F350, which is an aluminum body. I used 3M VHB tape to attach a 10" x 12" piece of 20 gauge galvanized sheet metal to the roof, which allows me to use a mag mount. The tape is only 1/16" thick, and the steel couples to the aluminum body like there was no gap at all. According to my SWR meter, there was no need to change the antenna tuning when going from my old steel body truck, to the aluminum body.

I would advise not putting a hole in the aluminum body to mount an antenna. The mount (likely steel) will cause galvanic corrosion in the aluminum. Even stainless steel can cause a problem.

 

[Motorradmark]

Good gouge.
Will give Dreadlocks idea a shot first- easiest. Guess I need to rustle up a swr meter to tell for sure.
4x4, never occurred to just mount the metal with vhb.
Thanks.

 

[DaveInDenver]

One thing to remember is having a low SWR measurement does not automatically mean you have assembled a highly functional antenna. A resistor presents a perfect load and will measure an almost perfect 1:1.

But this only means no RF is reflected not that all that RF was radiated. In the case of a resistor any RF power input was substantially converted to heat. So use the SWR measured to validate your design or installation.

As mentioned aluminum works just fine as an RF conductor and is effectively no different than copper or steel in most applications electrically. Mounting an NMO through an aluminum skin will work well. If you don't want to drill a hole or a roof rack will be in the way a bonding strap and rack mount is acceptable.

The problem of mounting on non-conductive or non-magnetic surfaces in fairly common since a lot of commercial vehicles use fiberglass and aluminum. The PCTEL K332 for example is a 6" diameter steel disc with a 3/8" hole punched in the middle used to when mounting an antenna on a non-conductive surface. It's sized to be a UHF ground plane with a 3/8" NMO mount. But similar solutions can be done using aluminum or copper foil, wire mesh, a disk or square you cut and mount with glue or tape.

 

[sonoronos]

The $50 nanoVNA that was recently released is something I would suggest to folks. Using it is much more definitive than using heuristics and internet guesses for antenna placement.

It's actually an unbelievable piece of kit for the price. I have probably spent $400 to 500 on antenna analyzers and SWR meters over the years and this thing just blows them all away.

The fact that a minimum wage worker can affordably calculate S-parameters up to 900MHz is mind boggling.

 

[Metcalf]

I used a painted steel disc that was bonded to the aluminum roof panel with some 3M VHB foam sheet on my LX45 project for a magnetic antenna.
So far it has worked out very well without requiring any holes. I have to pull the antenna down if I pull in the garage.