Brian; Regarding mobile jammers..
Many years ago I was faced with finding the cause of sporadic interference to a new 800 MHz trunked LMR system in Miami. This problem dogged several engineers and myself for months as the customer was reluctant to make final payment on the $8million system. The interference was received nicely by the many remote receivers throughout the city and disturbed the system audio and caused alarms to be reported. At street level, little was heard and when heard, it disappeared quickly. We could get weak intermittent signals from various rooftops and after a while it became obvious than _many_ emitters were responsible. Finally I had permission to bring a spectrum analyzer and antenna aboard a Miami PD helicopter while a co-worker with a spectrum analyzer took to the streets. About 10 minutes after taking off, I got a strong hit near a downtown parking lot. My coworker arrived and confirmed same hit. To make a long story short, it was the local oscillator of a Motorola MOSTAR radio. The problem was both a design problem of the mobile radio and more importantly a network design problem of the trunked system to be unable to deal with the momentary illegal carriers. (A point I argued with the product manager from the start).
Once we had the first interfering radio captured, we determined that they belonged to a radio system two counties away, and whenever they arrived in Miami, they would scan for a missing control channel and create havoc. To confirm this, I drove to the other county, and parked at a major intersection and took note of the commercial vehicles that drove by with their LO's leaking. This confirmed the model radio involved was limited to the one initially found.
This is documented in Chapter 2.7 of Gary C. Hess' book titled "Land Mobile Radio System Engineering. "
GPS jamming, intentional or not is pretty serious, and the FCC takes this seriously, but unless you have some pretty hard evidence they may not find it. If you have the time and equipment, you should monitor the L1 frequency from a high vantage point with a spectrum analyser to see if either it is a fixed emitter or mobile. If the latter, I would suggest doing as I did, set up a monitoring point at a traffic choke point to see if mobiles drive by that are emitting energy. A possible source is harmonic energy from mobile radio transmitters in the VHF, UHF, 700 and 800 MHz bands, or strong fundamental energy overloading the amplifed antenna to the point harmonics occur, or the MMIC amplifer is saturated. Someone on timenuts mentioned a GPS vendor who made a metal shield can to put over the GPS antenna that was essentially a waveguide slot/ bandpass filter. It was to test for out of band interference. This you might try at one or two sites. -- Joe Leikhim Leikhim and Associates Communications Consultants Oviedo, Florida [email protected] 407-982-0446 WWW.LEIKHIM.COM _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
