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2018 3.6R Touring
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Discussion Starter · #1 ·
My 3.6R Touring came with a set of Thule Aeroblade roof racks, these are longish airfloil-shaped crossbars. I'd like to put a 2m antenna on them but am struggling with finding a decent mount. Diamond makes a K500L, which looks to have a bracket on the leading edge and rubber strap on the trailing edge, I'm not sure how long that'll last.

Has anyone found a solid antenna mount that'll work on these things?
 

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2019 2.5i Premium w/Eyesight, "Wilderness Green Metallic"
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2018 3.6R Touring
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Discussion Starter · #5 ·
What did you end up doing?
After a lot of digging, I found that Diamond makes the K550L (Diamond Antenna K550 Series Luggage Rack Mounts K550L) that has a large enough clamp to fit around the Thule Aero Blade rack. Note that it's larger than the normal K550 and a lot of places aren't real clear on the different models (Even Diamond's site uses the K550 page for both models).

That, combined with a Diamond C213SMA (Diamond® Antenna ~ C213 Cable Assembly) that has a really thin cable that I can run through the door made for a decent non-permanent setup.

508479
 

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Cool! Looks pretty good, now I'm going to go look for it.
 

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So the entire 13'6" cable is small?
 

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2021 OB Touring, 2011 OB Premium
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What kind of performance are you getting without a ground plane?
Even with the antenna mounted a few inches above the roof, the roof should act as a ground plane. This looks like a nice setup.
 
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From the pic posted it does not appear that there's an effective ground plane as the base of the antenna appears insulated from the roof and the base of the antenna mount is not of sufficient size for an effective ground plane. (I could be wrong as I cannot see all the mounting details)

Being elevated the coupling to the roof is not effective as well. In my opinion to make it better he could attach a ground wire from the base to the car body somewhere close or fab up a ground plane something similar to what is shown here. (If the base of the mount is well grounded you can disregard my comments)

or

If he had access to a SWR meter he could see where the antenna was tuned & what the efficiency is. A high SWR indicates poor transmission-line efficiency and reflected energy, which can damage the transmitter and decrease transmitter efficiency. With that said, most well designed radios will fold back the power to avoid damaging the transmitter.

Just my 2 cents - Hope this helps.
 

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2021 OB Touring, 2011 OB Premium
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Because the roof of the car is at ground potential (it is part of the body which has a negative battery connection to it), it will act as a ground plane. The base of the antenna need not be physically connected to the roof. Grounding for the transmitter will effectively be through its mounts (if a mobile and connected physically to a metal part of the dash, for example) or the negative cable. Same with a hand-held, except ground will be effectively accomplished through the antenna cable.

The best thing to do is as was mentioned, check the Standing Wave Ration (SWR) with an SWR meter.
 

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Discussion Starter · #12 ·
This is just for a BCD436HP scanner that I use for long trips. It's far from an optimal antenna setup but it does kick butt over the duck that came with the handheld. :)

If/when I get around to putting a TX in, I'll have it professionally installed and actually put some thought into how/where it'll mount. Thanks for the feedback/links though, mobile antenna voodoo is something I have a lot to learn about.
 

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I built an NMO mount for a mobile antenna that attached to my Gen 5 roof rack where the tie-down loops were. The entire rack is made of plastic and is insulated from the car body. Most of the antennas I tried on the mount had a very high SWR on both 2 meters and 70cm. The only antenna that worked well was a ground independent half wave (such as a Comet SBB-5 ).

It was a bit longer than I wanted (38") and made quite a racket when I pulled in to the garage.

If you are just using a scanner, it's not a big deal. If you are transmitting, it is a big deal. Without a ground connection at the base of the antenna, the shield of the coax becomes a radiating element and the SWR goes whack. Magnet mounts work because the flat base of the antenna couples capacitively to the body of the car.

508622
 
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