Security For and From GPS

Per Enge [Professor of Aeronautics and Astronautics, Stanford University] Abstract: These days, GPS is used by all of us, and our application space is partially spanned by the following far-flung examples. Several hundred million GPS chip sets were shipped as part of cell phones last year, where they added about to the bill or materials. These will support consumer applications like location specific advertising. The same chip sets will save lives when associated with an emergency call from a distressed citizen. In addition, GPS is included in every new Boeing or Airbus jet, and these receivers cost over 000 each. The cost is dominated by the non-recurring cost associated with certifying a receiver for navigation at night or in bad weather. These GPS applications include location transactions of high value. The value may be economic or safety related. As this trend continues, the conspicuous vulnerabilities of GPS become more important. The GPS signals originate in medium earth orbits. After they have completed their 20000 kilometer journey to Earth, they have a received signal power of approximately 10^(-16) Watts (-160 dBW). These signals can be readily overwhelmed by inband transmissions from terrestrial sources. This radio frequency interference (RFI) can be scheduled (for military testing), accidental (eg harmonics from broadcast television), or malevolent. Malevolent RFI is also known as jamming and is routine for the modern car thief. GPS signals can also be …

Problem manifest itself in the moment after you release push to talk button and station don’t stop to transmitting. This is specifically for 2 meters band and not for 70 centimeters. You can see interesting videos on Youtube how to fix it with soldering capacitor on switch in the microphone housing. This is pretty good solution. I’ll explain why the problem exist and how to fix it on easier way if you are not so good friend with soldering iron. Explanation is easy if you know something about antennas. So, the problem is with RF (radio frequency interference). Why? The length of cable between headset connector and microphone/switch enclosure is 1 meter. In this cable you have one wire for ground, one wire for PTT button, one wire for microphone and one wire for speaker. So when you look two wires – ground and PTT you get beautiful full wave antenna for 2 meter band. You start transmitting and radio waves keep to make noises which radio use like the PTT button is pressed. One solution is to solder capacitor to switch in mic enclosure to change resonant frequency of (headset) wire antenna. Another way is to attenuate RF interference with feritte choke. Putting ferrite choke is noninvasive and pretty cheap solution. Thanks for watching! 73 Tom, 9A5TOM