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Scott Moore >That is a single frequency transmitter ? >Far more likely it was a broadband >source. What you are asserting is not logical. Rejection of single frequency >components is what spread spectrum is all about. Yes, but only if a) the wanted signals frequency at least occassionally hops to a value outside the interfering signals frequency range (or outside the passband range of any filters which are used to protect the receiver) and those excursions contain enough information to enable the receiver to reconstruct the data, or b) the frequency hopping pattern isnt known to the jammer, and the receiver is very selective. and c) the receiver has sufficient selectivity to not get swamped by the interfering signal. IIRC, GPS is some 10-20db below the noise floor, so you are relying heavily on the receiver working really well. The military use frequency hopping for covert comms but they dont tell you the pattern, and also I suspect they use a much wider frequency range than the very narrow range over which GPS does it. I did give a reference. I hope the report is still there. That Volpe Institute report on GPS vulnerability tells you, more or less, how to build a simple GPS jammer. It also tells you how to make GPS variously jam-resistant, but the techniques arent simple in terms of processing power or cheap - not if you want them to be really effective. None of this is really a problem provided there is a backup of some sort which isnt likely to get jammed at the same time - because anything short of a highly sophisticated (military) jammer should cause modern GPS receivers to report "bad reception" or whatever across the moving map. Peter. -- Return address is invalid to help stop junk mail. E-mail replies to zX80@digiYserve.com but remove the X and the Y. Please do NOT copy usenet posts to email - it is NOT necessary. |
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