As a RULE, we don't like to talk down communications products. As a HABIT, we feel responsible to make you aware of as much useful and helpful information as we can. With that in mind, we feel the need to discuss glass mounted CB antennas.
We receive more negative phone calls and e-mail on glass mounted CB antennas than any other antenna style on the market. If the complaint isn't "high SWR" and "poor performance" it will at least be "poor performance". Without exception, the person will ask, "What can I do to fix the problems I am having with my antenna?" Our response is always the same "If you have high SWR it will affect the antennas performance. Your antenna, like any 2-way antenna, must be tuned on the vehicle. However, if the SWR is acceptable but the performance is less than what you require or expect, you need a better antenna."
The "on-glass" cellular look-a-like antennas are, in our opinion, the worst performing antenna you can install on your vehicle. Uninformed users are easily led to believe that any antenna will fill their needs. So, they choose one that doesn't require extensive mounting considerations and will look "cool" on their vehicle. The biggest misleading factor is the "they work okay for cellular phones so they must be okay for CB" idea. Nothing could be further from the truth, and for good reason.
Cellular/ and PCS phones use a system of antennas and repeaters. Your transmission does not need to go very far before it locks into the system of repeaters. Once that link is made, the communication capabilities are unlimited. But with CB, communications are station to station. You do not have the advantage of repeaters so the antenna must do all of the work. As antennas go, there are inherent problems with the "on-glass" cellular look-a-like CB antennas. First of all, the RF signal must be coupled through the vehicle's glass. Glass, having good insulating properties, diminishes the signal strength to and from the radio. Then, if the glass has deicer wires, built in AM/FM antennas, or certain types of window tint, performance suffers further. To complicate matters further, the small size of the antenna reduces its ability to transmit as effective as a larger antenna. Also, because of the antennas slender stature, there is less antenna surface to gather the incoming signals. A common complaint from people that are using good antennas is that they can hear another station but the other station will not respond to their request for 2-way communication. What is happening is the good antenna is able to pick up the weaker signal from the wire antenna, but the wire antenna is either too short or too slender to receive your transmission. The other station just doesn't hear you!
At best, the glass mounted antennas, when properly installed and tuned, are suitable for vehicle to vehicle communications in a convoy situation where the distance between vehicles is minimal. If you are looking for more than that, they are a bad choice.