Glass mount vhf antenna?

[dixie729]

My brother has a new ford explorer. Im putting a Motorola CDM 750 vhf in it. He doesn't want to drill a hole in the roof, nor does he want to use a magnetic mount. I've found a glass mount vhf antenna with a mini uhf male connection that I need. My question is... has anybody used these glass mounts for vhf radios? Are they even worth the money? How good does it RX and TX?

 

[kayn1n32008]

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If no hole in roof, or a mag mount go with an 'L' bracket between the fender and the hood.

 

[stagnuts]

I have the glass mount on my car and have also put them on 3 of my 5 fire trucks. They work great. Great reception by Rx and Tx. Never had any complaints by either our member's or Fire control. So yes I would highly recommend them.

 

[Skypilot007]

Glass mounts are a slight compromise in performance but they do work. Every radio system is different and results will vary. You won't really know how good or bad it is until you try it out. Good luck.

 

[radionerd13669]

I have good success with glass mounts. I have found it also depends a lot on the brand. I have personally never used one but I have had no complaints from the ones that do

 

[dixie729]

Thanks for the input guys. I'll try it out and let everybody how it works out.

 

[n8zcc]

Glass mounts are a slight compromise in performance but they do work. Every radio system is different and results will vary. You won't really know how good or bad it is until you try it out. Good luck.

I don't think I can agree that glass mounted antennas offer a compromise in performance. The biggest problem is the glass followed by the location on the glass the antenna is mounted. This is what introduces compromise, not the antenna.

Through glass antennas are designed to take advantage of the capacitance of the glass during the design thus offering a matched coupling.

If the glass has metallic particles in it like some of the solar tint glass does this isn't going to work well. Also, mounting the antenna too low affects the radiation.

OP, search for how to identify metallic solar glass and check with the vehicle's manufacture.

Larson, in my opinion, makes the best.
Public Safety Antennas - Larsen Pulse

 

[jim202]

No matter how you look at it, glass mounts are a compromise. A VHF glass mount is not a very good choice. the largest reason is the coupling ability. Having a good relation with a number of the engineers at several of the antenna companies, they all say the same thing. It is very hard to get a good coupling through the glass at the VHF frequencies. This also causes an issue with the SWR.

Do as you think best.

 

[RodStrong]

Do as you wish, but I would go with an L bracket hood mount. I have had one on my personal rig for years, and it works great. Much better than an on-glass antenna IMO. Good luck either way.

 

[K9DAK]

I had a Larson KG-2/70 mounted low on the rear window (straddling the lowest defroster wire) on my old VW Golf and it worked great . . . worked a lot of VHF simplex with it. Then I moved it to my new VW Beetle in the same location and it may as well have been a wet noodle. Turns out the Beetle has a high metallic content in the glass.

So as the others have said, it may or may not work for you depending on location, type of glass, etc.

 

[dixie729]

Thanks guys. I'll look into it.

 

[popnokick]

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Metallic content of the window glass explains why there are such widely varied good/bad reports for on-glass antennas... even within this thread. So are there any standard markings on the glass or other method to determine metal content of auto glass? And I guess that question is for someone in the auto glass field.

 

[wa2chj]

I also have had mixed results with glass mount. The biggest problem I've had is the usually very narrow bandwidth of the glass mount antennas.

 

[W2NJS]

Radio frequency energy is an AC signal.
The glass acts as a capacitor.
Capacitors block DC and pass AC.
The on-glass antenna is designed to handle the capacitance introduced by the glass.
The antenna is furnished with a tuning network which must be set using a good wattmeter for VSWR.
Beyond that point you must have non-metallic glass, ideally, for the antenna to work properly.
Once you know what you're working with you can usually get an on-glass antenna to work fine.
The L-bracket also works fine, but it places the antenna relatively low and the RF may get into the vehicle's electronics when transmitting with the engine running.

 

[dixie729]

Sounds like Im gunna have to put my engineering skills to work and fabricate a bracket to maybe mount under the lugage rack or off the back hach of the explorer.

 

[cmdrwill]

Just make sure that the antenna mount is grounded to the vehicle's body, the ground IS one half of the antenna... Ground plane...

 

[K9DAK]

How About This?

Sounds like Im gunna have to put my engineering skills to work and fabricate a bracket to maybe mount under the lugage rack or off the back hach of the explorer.

You might try one of these . . . with two axes of adjustability you should be able to easily mount it on the rear hatch of the Explorer.

Diamond® Antenna ~ K400SNMO Trunk/Hatchback Mount

 

[dixie729]

Thanks K9DAK. I looked into one of those. The problem I ran into was the piece above the tail light on the rear hatch is plastic on the outside, Im not sure if the inside part is also plastic I'd have to look. the plastic piece runs from the tail light all the way to the roof. It's going to be mounted on a 2008 Ford Explorer.

 

[n8zcc]

No matter how you look at it, glass mounts are a compromise. A VHF glass mount is not a very good choice. the largest reason is the coupling ability. Having a good relation with a number of the engineers at several of the antenna companies, they all say the same thing. It is very hard to get a good coupling through the glass at the VHF frequencies. This also causes an issue with the SWR.

Do as you think best.

The engineers you have a good relationship with at several antenna companies must be the sanitation engineers. A competent RF engineer never would have said that.

You should not propagate false information, it only servers to confuse those who are learning and researching.

 

[n8zcc]

I also have had mixed results with glass mount. The biggest problem I've had is the usually very narrow bandwidth of the glass mount antennas.

How much bandwidth were you looking for?