The question was asked:: A more basic question. Do these degradations affect ordinary users? The reason I ask is that I have a GPS navigation system on in my truck 24/7 and use it every waking hour (I'm a retired engineer who's living a childhood fantasy - driving a long-haul 18-wheeler :-) Fairly frequently I experience fairly long intervals where the system goes completely dead. The satellite screen is all red - the system knows where the satellites are but no signal is received. This can last for miles. I've relocated the receiver, even stopping and removing the receiver from the truck just in case EMI was the culprit. Then just as quickly, the receiver gets lock and everything is fine.
The distance traveled - sometimes 10 miles or more - during an outage is such that ground interference can fairly confidently be eliminated. Almost all my running is on open interstates so ground factors can be eliminated. This is almost certainly a case of RFI from some nearby high-powered transmitter. As an example, if you are in northwest Baltimore (around Owings Mill) you will find some outages due to Maryland's PBS transmitter WMPT on Channel 67. Channel 67 has a video carrier @ 789.25 MHz. The second harmonic of these signals is 789.25*2 = 1578.5 MHz. The GPS L1 frequency which is used by all GPS receivers spans L1 = 1575.42 ± 1.023 MHz (to the first null of the CDMA spectrum. Receivers are typically ~1.8 MHz wide). It only takes a corroded telephone pole crossbar or a rusty barbed wire fence to act as a non-linear diode to make RFI that can wipe out GPS. The "bad" TV channels are 66 & 67. You can see a listing of channel 66 & 67 stations at [1]http://www.w9wi.com/tvdb/channels/66.htm & [2]http://www.w9wi.com/tvdb/channels/67.htm Other bad combinations can result when a VHF & UHF TV station mix to make a signal near the L1 frequency. If you want to play with the numbers, a listing TV frequencies and be found at [3]http://www.arrl.org/tis/info/catv-ch.html where the "AIR" channels at the top of the list are the ones of concern. Also note that the Channel 60-70 TV stations will be the "first to go" as broadcasters meet the mandatory 2009 HDTV rules. Channel 60-70 spectrum is supposed to be auctioned off to be used by police, fire etc emergency services. 73, Tom References 1. http://www.w9wi.com/tvdb/channels/66.htm 2. http://www.w9wi.com/tvdb/channels/67.htm 3. http://www.arrl.org/tis/info/catv-ch.html _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts