Signal Testing at Ankle Bracelet Position with Infra-Red Reflective Windshield

A test was conducted at an independent antenna range to determine the impact on signal strength of 

cell phone frequency signals at the position of an ankle bracelet typically used in tracking certain 

criminals. The test compared the signal strength between a car equipped with an Infra-Red (IR) 

Reflective windshield and the same car equipped with a standard windshield. A typical ankle bracelet 

uses cell phone frequencies to determine the location of the criminal so that the Corrections Bureau can 

track the criminal.

Test Results:

The testing was conducted for signal strength in the driver, front passenger, rear left and rear right 

passenger locations. The same vehicle was used for both the IR Reflective windshield and the standard 

windshield. The results show that there is no statistically significant difference between the car 

equipped with standard windshield and the IR Reflective windshield. The test was conducted with an IR 

Reflective windshield with no deletions, and with deletion only in the paint area of the windshield. 

Deletion in the paint area do not count towards the deletions allowed under the CARB Cool Cars 

Regulation.

The average signal strength varies a little depending on the location of the ankle bracelet. However, at 

any location, the difference between the IR Reflective windshield vehicle and the standard windshield 

vehicle is insignificant. It is also clear that the ankle bracelet signal is not affected by the deletions in the 

windshield.

Average Signal Strength 

(dBi)

Front

Driver

Front

Passenger

Rear

Driver

Rear

Passenger

Regular W/S -12.3 -10.3 -10.3 -8.7

IR Reflective W/S - 

No Deletions -13.1 -10.6 -11.0 -9.2

IR Reflective W/S - 

Edge Deletion -11.4 -10.3 -11.1 -9.1

Pittsburgh Glass Works, LLC

30 Isabella Street

Pittsburgh, PA 15212

Telephone (412) 995-6482

mrustagi@pgwglass.com

www.pgwglass.com

Mukesh Rustagi

Director, Strategic Product Management
Driver Foot Level Signal:

The driver foot level signal comparison shows that there is actually a better signal when the vehicle is 

equipped with an IR Reflective windshield than with standard windshield.

The average gain of the IR Reflective windshield with deletion in the paint area is actually almost 1 dB 

better than the standard windshield. The deletion in the paint area is typical of all IR Reflective 

windshields and is not counted towards the Tts calculation according to the regulation. We would 

consider this difference to be statistically insignificant and within the margin of error.

Front Passenger Foot Level Signal:

The comparison of this position shows no difference between the two windshield types.

-20.0

-18.0

-16.0

-14.0

-12.0

-10.0

-8.0

-6.0

-4.0

-2.0

0.0 824 829 834 839 844 849 868.5 874 879.3 883.6 889.4 894 1850 1860 1870 1880 1890 1900 1910 1920 1929.6 1938.4 1950 1960 1970.4 1980 1990 Average Gain (dBi)

Frequency (MHz)

Average Gain - Front Driver Seat

Regular W/S (Avg Gain -12.3 dBi)

No Deletion (Avg Gain -13.1dBi)

Edge Deletion (Avg Gain -11.4)

-20.0

-18.0

-16.0

-14.0

-12.0

-10.0

-8.0

-6.0

-4.0

-2.0

0.0 824 829 834 839 844 849 868.5 874 879.3 883.6 889.4 894 1850 1860 1870 1880 1890 1900 1910 1920 1929.6 1938.4 1950 1960 1970.4 1980 1990 Average Gain (dBi)

Frequency (MHz)

Cellular Average Gain -Front Passenger Seat

Regular W/S (Avg Gain -10.3 dBi)

No Deletion (Avg Gain -10.6 dBi)

Edge Deletion (Avg Gain -10.3)
Rear Driver Foot Level Signal:

The results from the testing of the signals from the rear driver location shows a difference of 0.8 dB. 

Once again, this is statistically insignificant and well within the margin of error.

Rear Passenger Foot Level Signal:

The test results for the rear passenger seat show a signal difference of 0.4 dB, which is once again 

statistically insignificant and within the margin of error. Essentially, there is no difference between the 

two windshields.

Conclusion

The ability to track an individual wearing an ankle bracelet is no different in a vehicle equipped with an 

IR Reflective windshield than in a vehicle with a standard windshield. There is no scientific basis for any

concern about the ankle bracelet issue associated with the Cool Cars regulation.

-20.0

-18.0

-16.0

-14.0

-12.0

-10.0

-8.0

-6.0

-4.0

-2.0

0.0 824 829 834 839 844 849 868.5 874 879.3 883.6 889.4 894 1850 1860 1870 1880 1890 1900 1910 1920 1929.6 1938.4 1950 1960 1970.4 1980 1990 Average Gain (dBi)

Frequency (MHz)

Cellular Average Gain -Rear Driver Seat

Regular W/S (Avg Gain -10.3 dBi)

No Deletion (Avg Gain -11 dBi)

Edge Deletion (Avg Gain -11.1dBi)

-2 0

-1 8

-1 6

-1 4

-1 2

-1 0

-8

-6

-4

-2

0 824 829 834 839 844 849 868.5 874 879.3 883.6 889.4 894 1850 1860 1870 1880 1890 1900 1910 1920 1929.6 1938.4 1950 1960 1970.4 1980 1990 Average Gain (dBi)

Frequency (MHz)

Cellular Average Gain -Rear Passenger Seat

Regular W/S (Avg Gain -8.7 dBi)

No Deletion (Avg Gain -9.2 dBi)

Edge Deletion (Avg Gain -9.1dBi)