General Consensus on Glass Mount Antennas

[HogDriver]

I'm considering a glass mount for my truck. I'd like to put an antenna right in the center of the roof but I can't as I park in the garage and it would get knocked off. Also considering sometype of trunk lid mount to put on the back hatch of my Explorer but that would be getting away from the center roof thing.

What is the general consensus on glass-mount antennas? are some decent enough to use? Something about not being directly connected bothers me but if there is a good antenna out there, I'll try it.

 

[mjthomas59]

Don't waste your time. Buy a hood/gutter nmo mount and enjoy the feeling of having increased range, better signal into your scanner, and never having to worry about your antenna falling off if you bang it on the roof of a parking garage or take it through a carwash.

Any window tint or defrost elements will greatly reduce the signal through a glass-mount antenna.

Although knowing what frequencies you listen to and the performance you expect from an antenna are important, i've used the radioshack glass mount and have found it just marginally better on 800mhz than a handheld scanner/antenna combo. If you are looking for long range reception or are planning on transmitting then forget the glass mount and find another way. Also, if you are planning on monitoring digital systems, the cleaner the signal you can get the better the audio will be coming from your scanner. Poor reception on digital equates to 100% unreadable digital noise. Considering a VHF 1/4 wave element is only 15-18 inches i'm surprised it won't clear your garage, but even still i'd go with the hood mount or hatchback mount.

 

[zz0468]

I wouldn't go so far as to say 'don't waste your time'. It really depends on what your goal is. They are ALWAYS a compromise. For the cost of reduced performance, you get a neat, professional looking antenna without drilling holes. If performance is your primary goal, then you need to drill the holes.

For what it's worth, the performance hit is probably 3-6 db - noticeable, but not the end of the world. You mention concern about being away from the center of the roof. Remember, the glass mount antenna is going to not only be away from the center of the roof, it's also got that added loss.

 

[key2_altfire]

I had a glass-mount antenna that seemed to have some deaf spots, so I asked one of the engineers where I work to sweep the coupler for me on his network analyzer. It coupled just great in VHF (about 1.5 dB loss); over about 200 MHz it got really deaf, but surprisingly coupled ~800 MHz with about 1 dB loss.

 

[rfradioconsult]

I had a glass-mount antenna that seemed to have some deaf spots, so I asked one of the engineers where I work to sweep the coupler for me on his network analyzer. It coupled just great in VHF (about 1.5 dB loss); over about 200 MHz it got really deaf, but surprisingly coupled ~800 MHz with about 1 dB loss.

If it was swept with a network analyzer, you are looking at the return loss. You want a negative number to indicate return loss, higher the better such as -16 dB.

 

[HogDriver]

Thanks...question answered.

 

[hamstang]

I have used a Larsen Dual Band (VHF-UHF) glass mount for ham radio with excellent results for several years. I have even used a "remount" kit to install the antenna to a different vehicle. I don't know how it would receive for 800mhz, but VHF-UHF should be very good. Larsen antennas aren't the cheapest out there, but I have had decades of excellent experience with 'em........

 

[N1BHH]

How much clearance do you have there? Try the Larsen NMO-150/450/800 as it's only 14 inches tall and easily mounted on the roof. Also there is a Comtelco antenna which is about the same height and can be found here: http://www.scannermaster.com/Comtelco_All_Band_Low_Prof_Antenna_p/07-540719.htm

 

[rankin39]

On-glass antenna.

I have used a Larsen Dual Band (VHF-UHF) glass mount for ham radio with excellent results for several years. I have even used a "remount" kit to install the antenna to a different vehicle. I don't know how it would receive for 800mhz, but VHF-UHF should be very good. Larsen antennas aren't the cheapest out there, but I have had decades of excellent experience with 'em........

I can second that. I used the same antenna on my wife's Saturn wagon (that had a non-metalic roof, so no mag mount was possible) and it worked very well on 2 meters and 440 MHz. With that antenna, it's important to keep the coax at the length that comes with the antenna, as it is part of the resonating apparatus.
On the other hand, I tried an 800 MHz. on-glass antenna and it was virtually a total failure. Not nearly as good for reception as a mag mount on the roof. It sort of depends on how close you are to the transmitter. If you're several miles away, I'd say to skip the on-glass 800 MHz. antennas. I find that the little Larsen tri-band scanner antenna works well for me.
Bob, w0nxn