NMO Mount with Factory Roof FM Antenna Hole

[alexing73]

Hi all,
Yesterday, I was looking at my ugly mag-mount U/V antenna I have on my trunk (2008 Ford Fusion), and had an idea. I don't use the AM/FM or Sirius functionality in my car (my phone has all the music I'll ever need), and I've already purchased a stubby replacement antenna mast for the factory antenna on the roof to get it out of the way- so would it be possible to just pull that off and put an NMO mount up there? I spent an hour or two pulling the headliner down and awkwardly reaching around it to unscrew the factory antenna and get some measurements; the factory hole is 2x3cm with a little 2-3mm wider spot spanning approximately 1.5cm along the left side of the hole (see photos). This obviously won't work with the standard through-hole 3/4" NMO mounts that you can find online everywhere, so I started researching and weighing my options. Those are as follows:

1. Combination GPS/NMO Mounts
   1. Motorola PMAN4004 [Expensive, no comprehensive measurements available]
   2. Larsen NMOHFGPS Series [Expensive, ratings indicate an unreasonably high SWR even though it isn't an antenna itself (2:1?)]
   3. Browning BR-2100-CUHF/MUHF [Impossible to source]
   4. Panorama GPSNMO [Impossible to source/manufacturer will only offer quotes, not prices]
2. Breedlove Mounts + PL-259/RG58 Cable
   1. 2" Roof NMO Mount
   2. 3" Roof NMO Mount
3. Drilling another hole isn't an option
   1. The sunroof mechanisms extend almost completely to the factory antenna
   2. There isn't hardly any room behind the factory antenna
   3. Trunk holes aren't an option, either, as the trunk has thick steel strengthening ribs under the sheet metal
   4. The parents (thanks for the car, guys!) wouldn't have it

I was wondering if anyone has any alternative ideas that would be cheaper, as 4-year engineering schools are, in fact, not cheap. Any and all suggestions are welcome. Thanks in advance!

Photos

 

[mmckenna]

You could use one of these, or any of the similar style antennas:

Panorama Antennas | Panorama Antennas

Established in 1947, Panorama Antennas is a global leader in the design and manufacture of RF antenna solutions for wireless communications.

www.panorama-antennas.com

The base is big enough to cover the hole. A washer underneath will hold it in place.
They don't make a dual band whip that I'm aware of, but a 1/4 wave VHF antenna will be 3/4 wave on 70cm. It'll tune up just fine, but have a less than ideal radiation pattern.

Not cheap, but it's an option.

 

[iMONITOR]

Maybe something like this. You might have to fabricate some type of large flat washer.

Hocky Puck Antenna

hockey puck antenna - Google Search

:

 

[mmckenna]

Maybe something like this. You might have to fabricate some type of large flat washer.

They are lousy on VHF, beyond lousy. They'll not cover the full 2 meter spectrum, they are limited in how much power they will handle, and they have poor performance on VHF. I've had people try to give them to me. They buy them and discover just how horrible they are, they get removed a few days later and end up on a shelf.

They will work on UHF and above.

 

[alexing73]

I couldn't find any shark fins or pucks that looked to be any good at all on 2m. Instead, I'm now researching using a thick surface 3/8" hole NMO mount from Laird in combination with a fender washer (or two, one for the bottom) and rubber seal underneath. It'd end up being a sort of homemade version of the Breedlove Mount. I'm just not sure how much less ugly that would be than the mag mount...

 

[iMONITOR]

They are lousy on VHF, beyond lousy. They'll not cover the full 2 meter spectrum, they are limited in how much power they will handle, and they have poor performance on VHF. I've had people try to give them to me. They buy them and discover just how horrible they are, they get removed a few days later and end up on a shelf.

They will work on UHF and above.

True. The O.P. wasn't specific about what bands he would be using it for, so I guess out of habit I was assuming it was for the 850MHz band. They seem to work fairly well for that.

 

[mmckenna]

True. The O.P. was specific about what bands he would be using it for, so I guess out of habit I was assuming it was for the 850MHz band. They seem to work fairly well for that.

Yeah, they do. I have some on a few of the garbage trucks at work. Can't tell the difference between them and a 1/4 wave whip.

 

[krokus]

What about a lip mount, or an on-glass? They are not optimal, but might be better than modifying the body hole.

 

[engineercarl]

Have to considered looking at TESSCO for a "disguise" antenna that is identical to the form and fit of the stock antenna, but has TX/RX for what you need? It would seem to me that STI-CO might make an antenna that would look identical to the stock arrangement.

Yes, you're going to take a hit in the performance vs a standard dual-band whip, but it's ultimately going to depend on you. Look at what State/Federal Agencies are doing for low profile installations.

EC

 

[alexing73]

Thanks for the responses, everyone. Also, my apologies for not clarifying- I use the 2m and 70cm bands for TX/RX and then scan tons of stuff between 140-170Mhz.

What about a lip mount, or an on-glass? They are not optimal, but might be better than modifying the body hole.

I have considered the lip mount, but I believe the lip on my trunk might be angled too much. Its slope increases as it approaches the rear window to have a seamless look, but it's not so great for vertically polarized signals. As for the on glass mounts, I don't have a lot of faith in them for weak signals. Thanks for the reply nonetheless.

Have to considered looking at TESSCO for a "disguise" antenna that is identical to the form and fit of the stock antenna, but has TX/RX for what you need? It would seem to me that STI-CO might make an antenna that would look identical to the stock arrangement.

Yes, you're going to take a hit in the performance vs a standard dual-band whip, but it's ultimately going to depend on you. Look at what State/Federal Agencies are doing for low profile installations.

EC

The intent was more to find something on the ultra-cheap end. STI-CO's covert antennas are absolutely wonderful, but the price tag hanging from them isn't quite as wonderful. Thanks, though!

In the end, I've settled on a homebrew mount that should honestly be just fine. I went to Lowe's and grabbed some 1/8" thick 2" x 1/2" fender washers and some rubber washers in the same size. The plan is to put a metal washer under the sheet metal, a rubber one on top, and then a metal one spray-pained black on top of the rubber one. The surface ends up being about 7/16" thick. Then, I'll take a thick-surface NMO mount from Laird and put through all of that business. Last, I'll top it all with a Larsen NMO2/70SH- an antenna with a great reputation and a small footprint (only 19" whip). If anything goes wrong, I always have the option of throwing the stock FM antenna back up on the roof to seal the hole, and I'll probably just put the antenna on a mag-mount NMO deal until I get another car or the permission/materials needed to put holes in the body.

 

[iMONITOR]

What about a lip mount, or an on-glass? They are not optimal, but might be better than modifying the body hole.

Those sound like painful suggestions!

 

[engineercarl]

Comet's lip mounts have an elbow that can be tightened to keep the radiator vertical. One guy here at work actually had the lip mount 90 degrees from the vertical and still had the antenna straight up and down.

Just one idea.

EC

 

[alexing73]

Comet's lip mounts have an elbow that can be tightened to keep the radiator vertical. One guy here at work actually had the lip mount 90 degrees from the vertical and still had the antenna straight up and down.

Just one idea.

EC

I'll keep that in mind as a backup. Thanks!