[PPRAANet] Glass Mount Antennas

[NØABC -- Dennis]

I recently, within past two months, finally applied another Radio Shack 
19-324 dual-band glass mount antenna to the windshield of my '95 Ford Escort 
wagon. I had this antenna hanging in the basement since I picked it up circa 
1999. I said "another" back there because I had the first one on my '90 Geo 
Prizm since 1996 - until I sold the car in 2014. I managed to remove that 
original after a lengthy process of slowly wedging a single-edge razor blade 
between it and the windshield. It was definitely on there to stay. It 
performed quite well for all 18 years, and now the new (old) one seems to be 
as well. The SWR on this last one is OK - not spectacular - but it gets the 
job done.

That being said, all of the new glass mount antennas have an obvious caveat 
applied to their descriptions, packages,  and instructions. I'll try to find 
it real quick and paste here..........

>From k0bg.com/options.html:
"Virtually every vehicle made today uses passivated glass (sometimes called 
solar glass). Embedded in the glass are metallic particles which serve 
several purposes. First, they block most UV rays which lessens fading of the 
interior trim pieces, and they reduce the heat load. Less air conditioning, 
better fuel mileage. To a lessor degree, the metallic particles act as RF 
shield for the digital electronics inside the vehicle. The filtered 
wavelengths include those used by amateurs, cellular phones, automated toll 
readers, radar detectors, and GPS devices.

"Glass mount antennas rely on capacitive coupling. Both passivation, and the 
thickness of the glass have an effect on the amount of absorption at the 
various wavelengths. These facts make glass mount antennas nearly worthless. 
Worse, glass mount antennas do not have a ground plane under them. This 
causes the return currents to flow on the outside of the coax (common mode), 
thus the coax does the majority of the radiation. Whether or not any given 
installation can make contacts using a glass mount antenna is moot. The fact 
remains, Larsen, the largest maker of glass mounts, doesn't recommend 
mounting them on passivated glass. The best advice I can give anyone about 
using glass mount antennas is this; don't!"

I don't fully agree with those comments, as in my cases, they DO work. 
However, you've got to ensure you do not have passivated glass, AND you must 
be meticulous about the proper and accurate mounting - the antenna base and 
coupler box must be precisely aligned and mounted to the glass - opposite 
each other.

Good luck!

73

Dennis
N0ABC

-----Original Message----- 
From: Michael Derbort
Sent: Wednesday, April 20, 2016 10:26 AM
To: ppraanet at mailman.qth.net
Subject: [PPRAANet] Glass Mount Antennas

Hello all,



Quick question for you.  Does anyone have any experience with glass mounted
antennas?  Do they work well?  Not worth it?  Some better than others?  Let
me know your thoughts?



Michael E. Derbort, KC0ELG



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