Re: [time-nuts] Slightly OT - GPS-Based Accurate Direction Finding
On Aug 25, 2010, at 9:04 PM, David Smith da...@smithfamily.net.au wrote: As a fair percentage of the discussion amongst the learned gentlemen on this group involves GPS-based timing systems, I'd like to ask a non-time related, but GPS-related question. As part of microwave radio experimentation, often on windy hilltops, I have a need to find direction very accurately. I have seen advertised GPS-based Azimuth Pointing Systems such as this: http://www.ascscientific.com/APS.html However they are a little (lot) out of my budget range. The system seems to work by taking the raw satellite phase information from two separate GPS systems and crunching the data to come up with an azimuth figure. Has anyone heard of a (Open Source?) program that could be used to do these calculations? Regards, David Smith David, Please see U.S. Patent # 5,777,578 GPS Compass. I can send you a copy if you cannot find it. Bruce, WB9ANQ -- Bruce Rahn Wisdom has two parts: 1. having a lot to say; and 2. not saying it! ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)
Magnus Danielson wrote: The directional antenna needs to have their directional lobes towards each sat being tracked. If you try put the nulls towards the jammers then you need to have a fair knowledge of where it is. If you direct the loop, the side-loobs needs to be sufficiently suppressed. A single jammer and a fair idea of the heading will work, but it becomes complex and in the end you need more and more antennas to handle more jammers. Ah...you really don't need any a prori knowledge of the location of a jammer. A little reading on adaptive antenna technology as applied to GPS will throw light on my comment and is also some interesting reading. This would be a starting point: http://www.raytheon.com/businesses/stellent/groups/sas/documents/content/cms04_022900.pdf Bruce, WB9ANQ -- Bruce Rahn Wisdom has two parts: 1. having a lot to say; and 2. not saying it! ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)
Hal Murray wrote: cfhar...@erols.com said: What makes you think it needs to be CW, and cannot be pulsed and chirped? All it has to do is confuse the receiver enough so that you can't trust its readings. Why is pulse or chirp likely to be more confusing per W of jamming power? Perhaps this reference will answer some of the questions present here: http://www.navcomtech.com/Support/Download/Sapphire%20Jamming%20Test%20Report%208%20Jan%202007v3.pdf One factor I have not seen anyone address is the effectiveness of jamming as a function of the receiver state. A GPS receiver will be much more susceptible to jamming when it is trying to acquire and lock onto a satellite signal than it is after lock and tracking has been achieved. Bruce, WB9ANQ -- Bruce Rahn Wisdom has two parts: 1. having a lot to say; and 2. not saying it! ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] old HP application notes
Dr Bruce Griffiths wrote: I have just unearthed HP application notes: 301-1: Low noise division of 10MHz oscillators and 935: Microwave power generation and amplification using impatt diodes Anyone interested in scanned copies? Yes please! Be well -- Bruce -- Bruce Rahn Wisdom has two parts: 1. having a lot to say; and 2. not saying it! ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] GPS Jamming in the UK
[EMAIL PROTECTED] wrote: I've not come across this before and when a friend first fowarded the link from another group I thought it was a spoof, and still only half convinced:-), but I've just copied this from the official Ofcom Website in the UK.. The Ministry of Defence conduct occasional tests on military systems which may result in some loss of service to civilian users of the Global Positioning System (GPS) including in-car navigation devices and networks which rely on GPS signals. Ofcom seeks to provide citizens and consumers with information about possible interruptions to these services via these email updates giving advanced notification of these tests. It must be emphasised that this notification process only warns of future jamming excercises that are brought to the notice of Ofcom and may not cover all jamming exercises. It cannot be assumed that any loss of service is due to jamming exercises. There's an option to sign up for email notification. _http://www.ofcom.org.uk/static/subscribe/select_list.htm_ (http://www.ofcom.org.uk/static/subscribe/select_list.htm) Anyone come across this before or actually experienced any identifiable jamming of signals? regards Nigel GM8PZR Nigel, GPS 'denial of service' (aka jamming) tests are fairly common here in the US. In 'another life', I was involved with them. Public notice is given in advance of planned testing. You might find this link of interest: http://www.fly-low.com/features02/gpsdenial.html This link provides a listing of past, current, and future denial of service tests: http://www.navcen.uscg.gov/gps/gpsnotices/GPS_Interference.pdf There have also been documented cases of inadvertent/unscheduled tests. With a little bit of searching, you can find them :) What you're reading about is real! Hope this helps a little. Bruce -- WB9ANQ -- Bruce Rahn Wisdom has two parts: 1. having a lot to say; and 2. not saying it! ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS Jammers
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Magnus Danielson wrote: ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY From: Brooke Clarke [EMAIL PROTECTED] Subject: Re: [time-nuts] GPS Jammers Date: Tue, 13 Nov 2007 17:11:46 -0800 Message-ID: [EMAIL PROTECTED] ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Hi Tom: I've also seen the three antenna version on the asian discount web pages. Do you know if any of them have test reports? I question of the one that looks like a cigarette lighter with a 1 whip antenna can do much. 10 km radius have been measured with similar properties. Cheers, Magnus It really doesn't take much! One of my favorite GPS jamming incidents of public record is the one at the link: http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=43404 For another look at things, please see: http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=43432 Bringing this back on the topic of time :) The Fall 2007 issue of the magazine Inside GNSS has an interesting article Fuzzy Time - GPS-Based Synchronizers in the Presence of Interference For a CW signal, a GPS timing receiver's performance begins to degrade when the interfering signal is at a level of -87 dBm. With an FM interference source, it starts to degrade at -106 dBm. Well worth the read if you can find this magazine. Bruce -- Bruce Rahn Wisdom has two parts: 1. having a lot to say; and 2. not saying it! ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
