Re: [time-nuts] How hard is it to detect a GPS Jammer?
I for one would insist on complete situational awareness at all times. The alternative is being LOST. That can be bad for one's health. The last time I was willingly lost was when Betty and I were returning from the Palace Real in Madrid and we decided to just start walking to the east. Then there is the Maze at Hampton Court. Of course we weren't really lost, but merely in a state of degraded situational awareness. On 10/07/2013 09:30 PM, Bill Hawkins wrote: In general, we expect a jammer to be involved in criminal activity. What about a wilderness guide whose reputation is built on finding the best spots to view Nature's wonders. Should he or she be happy to let people in the guided group save the coordinates of those spots in order to compete with the guide or avoid guide's services in the future? Or would that be a justifiable use of jamming? Hypothetically speaking, of course. Bill Hawkins ___ 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. -- Chuck Forsberg WA7KGX c...@omen.com www.omen.com Developer of Industrial ZMODEM(Tm) for Embedded Applications Omen Technology Inc The High Reliability Software 10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430 ___ 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] How hard is it to detect a GPS Jammer?
Le 8 oct. 2013 à 10:29, Chuck Forsberg WA7KGX a écrit : I for one would insist on complete situational awareness at all times. The alternative is being LOST. That can be bad for one's health. That is not the same as not wanting to be FOUND. ___ 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] How hard is it to detect a GPS Jammer?
And some of them have considerably higher EIRP, Like THIS one, As you can see they are not sophisticated devices they are intended to swamp the real GPS signal, Spoofers would be much harder to detect which is why GNSS systems intended for military use rely on encrypted signals and fairly sophisticated key management techniques. Now for nightmares - the GPS Jammer shown below has an advertised EIRP of 3.4W and the vendor has another with an EIRP of 7.2W http://hem.passagen.se/communication/gps.html [image: Inline image 1] On Mon, Oct 7, 2013 at 9:11 PM, Jim Lux jim...@earthlink.net wrote: On 10/7/13 8:31 AM, Chris Albertson wrote: OK so let's say you have a receiver and detect a certain about of power at the right frequency. How do you determine which of three cases you have (1) an actual GPS signal from a satellite. (2) a spoofer (who tries hard to look like #1) or (3) a jammer. The jammers put out many milliwatts and have enormous signals that are obvious on a spectrum analyzer. GPS signals are invisible on a spectrum analyzer, normally. IN fact, most GPS receivers don't work very well if there are signals above the noise floor: they depend on the noise to make them work with their mighty 1 bit quantizers. Spoofers are a real problem. I doubt anyone is selling spoofers on eBay. Sure, one can probably find some code to run on a USRP from some grad student's project. So the easiest thing to detect would be a cheap, GSP jammer that is moving. You could use multiple receivers to triangulate the location and then determine it is not in orbit and is not a reflection from a metal roof or something.The problem is the jammer's very low power. These things are inteneded to only cover a tiny area They are not designed with coverage area in mind. They are basically whatever power the VCO puts out coupled to the antenna From a jamming standpoint, they're not very sophisticated. As a result they dump out something like +10dBm. So running a quick Friis formula link budget, and assuming you want to have a Prec of around -100dBm (10 MHz BW, kTB) 110 = 32+ 20*log10(1575) + 20*log10(d) 110-32 - 25 = 20*log10(d) d = 400 km... This is why they are such a problem __**_ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/** mailman/listinfo/time-nutshttps://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. GPS-JAMMER.gif___ 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] How hard is it to detect a GPS Jammer?
Hi But there's obviously something wrong with the 400 KM number. 1) If +10 dbm is good enough to burry a useful signal at that distance, it should be good enough to communicate at that distance. That's pretty impressive QRP without high gain / directional antennas involved. 2) The radios (at least the modern ones) do have CW signal immunity. Weather that's 60 db or something else probably varies with the make / model of the GPS. How well that works with a VCO jammer - again, a that depends sort of thing. 3) There's a (maybe) 40 db variation in GPS signals. To deny service you need to take out the strong ones, not just the weak ones. 4) Even without specific anti-jam in the GPS, the code it's self does have some immunity to a jammer. Of course you don't have to look very far into the archives to find wonderful examples of slipped decimal points in my posts…. Bob On Oct 7, 2013, at 9:11 PM, Jim Lux jim...@earthlink.net wrote: On 10/7/13 8:31 AM, Chris Albertson wrote: OK so let's say you have a receiver and detect a certain about of power at the right frequency. How do you determine which of three cases you have (1) an actual GPS signal from a satellite. (2) a spoofer (who tries hard to look like #1) or (3) a jammer. The jammers put out many milliwatts and have enormous signals that are obvious on a spectrum analyzer. GPS signals are invisible on a spectrum analyzer, normally. IN fact, most GPS receivers don't work very well if there are signals above the noise floor: they depend on the noise to make them work with their mighty 1 bit quantizers. Spoofers are a real problem. I doubt anyone is selling spoofers on eBay. Sure, one can probably find some code to run on a USRP from some grad student's project. So the easiest thing to detect would be a cheap, GSP jammer that is moving. You could use multiple receivers to triangulate the location and then determine it is not in orbit and is not a reflection from a metal roof or something.The problem is the jammer's very low power. These things are inteneded to only cover a tiny area They are not designed with coverage area in mind. They are basically whatever power the VCO puts out coupled to the antenna From a jamming standpoint, they're not very sophisticated. As a result they dump out something like +10dBm. So running a quick Friis formula link budget, and assuming you want to have a Prec of around -100dBm (10 MHz BW, kTB) 110 = 32+ 20*log10(1575) + 20*log10(d) 110-32 - 25 = 20*log10(d) d = 400 km... This is why they are such a problem ___ 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. ___ 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] How hard is it to detect a GPS Jammer?
On 10/8/13 4:17 AM, Bob Camp wrote: Hi But there's obviously something wrong with the 400 KM number. 1) If +10 dbm is good enough to burry a useful signal at that distance, it should be good enough to communicate at that distance. That's pretty impressive QRP without high gain / directional antennas involved. 2) The radios (at least the modern ones) do have CW signal immunity. Weather that's 60 db or something else probably varies with the make / model of the GPS. How well that works with a VCO jammer - again, a that depends sort of thing. 3) There's a (maybe) 40 db variation in GPS signals. To deny service you need to take out the strong ones, not just the weak ones. 4) Even without specific anti-jam in the GPS, the code it's self does have some immunity to a jammer. Of course you don't have to look very far into the archives to find wonderful examples of slipped decimal points in my posts…. You're right, I forgot the process gain of the despreading. Assuming you're going from 1 Mchip/sec for the C/A code to 50 bps for the nav message, that's 43 dB That alone gets you to 2km jamming range from 400km, but that also assumes that the jamming signal doesn't inhibit acquiring the code and despreading. As Dixon's book on Spread Spectrum says, acquisition is the hard part; because you don't have the process gain yet. I suppose with a parallel acquisition strategy, you're basically trying all codes, and that might be able to work. But even so, those sorts of process gain arguments don't necessarily work if the receiver has a hard limiter or quantizer in it. I don't know that modern consumer GPSes have CW immunity. If they're using a 1 or 2 bit quantizer, a strong CW signal pretty much captures the front end. Easy to try. Let me just fire up my kilowatt 1.5 GHz transmitter heregrin ___ 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] How hard is it to detect a GPS Jammer?
It does no good to prohibit clients from using GPS on land because unless you keep them blindfolded the entire time they will see and photograph their surroundings. People with some training can find location to within about 25 feet with no GPS even in a flat dessert. I've hiked out to find a tent stake that was placed there by an instructor in open dessert. We photo the stake then hike back. THose who don't know the tricks can certainly find a location to within a 1/2 mile. The only place this makes sense is on the ocean when you are not within sight of land. There ARE some fishing boat captains who ask clients not to use the GPS. But people cheat and turn on the GPS and leave it packed in a bag and let it run until the battery dies. This way they are never seen using it.This is rare because usually fish move and yesterday's good spot is of no use. Many of the boats hire a spotter who works from an airplane. But then everyone uses one of only two spotters who fly in the area. On Mon, Oct 7, 2013 at 10:37 PM, David I. Emery d...@dieconsulting.comwrote: On Mon, Oct 07, 2013 at 11:30:57PM -0500, Bill Hawkins wrote: In general, we expect a jammer to be involved in criminal activity. What about a wilderness guide whose reputation is built on finding the best spots to view Nature's wonders. Should he or she be happy to let people in the guided group save the coordinates of those spots in order to compete with the guide or avoid guide's services in the future? Or would that be a justifiable use of jamming? No. Jamming can potentially impact a much wider area and safety of life critical uses of GPS, and very few wilderness guides are expert enough to understand, control and mitigate this risk. And even if one particular one was, how is this to be reliably ensured ? Should he or she be licensed and certified and regulated as to how and when he might jam safely - we don't current issue GPS denial licenses (except maybe to LightSquared) ? And even with someone suitably trained and licensed and certified there is a balance between the slight risk that his jamming harm something important or critical that society relies upon and his own personal interest in denying GPS to his customers that I am not sure we as a society have quite figured out. Should private businesses be allowed to deny GPS (or for that matter cellphone access) to folks nearby or their customers - is this a legitimate interference with a public resource ? Obviously if the answer is yes, businesses should be allowed to jam cellphones or GPS - then what are the limits - eventually all those private jammers will make such services MUCH less useful - as they will be unpredictably unreliable at apparently random times and places which makes it very hard to trust them for anything important. We will in other words have allowed the private interests of certain folks to destroy a commons, something we are getting increasingly good at BTW. I suppose it is SOMEWHAT justified for a guide to search his customers for GPSes, or have a strict policy of dropping them off at the nearest road if they are found to be using one, or even to use a GPS detector to ID GPSes in use... but an active attack seems wrong given the risks involved. And anything more nuanced in a policy on such invites various low life scumbags to push the limits and use blatantly excessive power, dangerous antenna locations, and generally horrid engineering that puts important uses and users of the technology at serious risk for very selfish personal reasons - perhaps in some cases just buying some cheapo jammer instead of a proper licensed and limited one managed and installed by someone who knows what he is doing. Finally of course, who is to say that I cannot use my cellphone for important messages - perhaps life critical (my wife is a doctor and does this from time to time when she is on call)... or my GPS to locate a store somewhere... perhaps if the jamming ONLY worked in a completely private space owned or controlled by the jammer and not at all outside of it would this begin to be marginally acceptable but it certainly isn't in public spaces. And I believe there should be mandatory readily visible notices saying that jamming is use... allowing someone who truly needs access to know what is happening. As for the wilderness case specifically there are any number of strategies to defeat short range jamming of that sort - just announce you have to go as the group leaves the scenic knoll and go back and take a bearing (maybe automatically from a concealed GPS you already have in you backpack) while peeing on the special rock... Inverse square law applies here of course... hard to radiate enough power to deny over a long enough distance without being completely unsafe for other users. -- Dave Emery N1PRE/AE,
Re: [time-nuts] How hard is it to detect a GPS Jammer?
On 10/07/2013 01:36 PM, Bob Camp wrote: Hi Anything that will receive up there should be able to tell you when a jammer comes by. The issue is that not a lot of gear is made for that band (other than GPS receivers). The easy approach would be to use a modern GPS module that puts out noise level / jamming information. Turns out they are not that good. AGC detection based works fairly well. Cheers, Magnus ___ 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] How hard is it to detect a GPS Jammer?
Hi Well finding a +10 dbm 1.5 GHz transmitter isn't very hard to do at all. I've got several of those…. Bob On Oct 8, 2013, at 9:42 AM, Jim Lux jim...@earthlink.net wrote: On 10/8/13 4:17 AM, Bob Camp wrote: Hi But there's obviously something wrong with the 400 KM number. 1) If +10 dbm is good enough to burry a useful signal at that distance, it should be good enough to communicate at that distance. That's pretty impressive QRP without high gain / directional antennas involved. 2) The radios (at least the modern ones) do have CW signal immunity. Weather that's 60 db or something else probably varies with the make / model of the GPS. How well that works with a VCO jammer - again, a that depends sort of thing. 3) There's a (maybe) 40 db variation in GPS signals. To deny service you need to take out the strong ones, not just the weak ones. 4) Even without specific anti-jam in the GPS, the code it's self does have some immunity to a jammer. Of course you don't have to look very far into the archives to find wonderful examples of slipped decimal points in my posts…. You're right, I forgot the process gain of the despreading. Assuming you're going from 1 Mchip/sec for the C/A code to 50 bps for the nav message, that's 43 dB That alone gets you to 2km jamming range from 400km, but that also assumes that the jamming signal doesn't inhibit acquiring the code and despreading. As Dixon's book on Spread Spectrum says, acquisition is the hard part; because you don't have the process gain yet. I suppose with a parallel acquisition strategy, you're basically trying all codes, and that might be able to work. But even so, those sorts of process gain arguments don't necessarily work if the receiver has a hard limiter or quantizer in it. I don't know that modern consumer GPSes have CW immunity. If they're using a 1 or 2 bit quantizer, a strong CW signal pretty much captures the front end. Easy to try. Let me just fire up my kilowatt 1.5 GHz transmitter heregrin ___ 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. ___ 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] How hard is it to detect a GPS Jammer?
Hi Anything that will receive up there should be able to tell you when a jammer comes by. The issue is that not a lot of gear is made for that band (other than GPS receivers). The easy approach would be to use a modern GPS module that puts out noise level / jamming information. Bob On Oct 7, 2013, at 12:59 AM, Hal Murray hmur...@megapathdsl.net wrote: The recent discussion of solar flares screwing up GPS timing was interesting. I just watched Todd Humphreys TED talk again. He's focused on location, but does mention time in terms of stock exchanges. Todd Humphreys: How to fool a GPS http://www.ted.com/talks/todd_humphreys_how_to_fool_a_gps.html He's got a good discussion of GPS jammers and spoofers, but no geeky details. What's the spectral/power output of the typical eBay GPS jammer? Suppose I lived near a major highway. Could I build a receiver that would count jammers driving by? Could I track them (at least somewhat) with a directional antenna on a rotator? Is this something semi-geeky amateurs could contribute to? What sort of gear has harmonics in the GPS band? -- I assume people are familiar with the trucker who jammed the FAA test in NJ. Here is a good story: http://www.insidegnss.com/node/3676 That article has a link to commercial gear targeted at this market. http://www.exelisinc.com/solutions/signalsentry/Pages/default.aspx The graphics shows 3 receivers is a port/harbor setting. -- These are my opinions. I hate spam. ___ 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. ___ 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] How hard is it to detect a GPS Jammer?
Many scanners now go to that frequency e.g AOR AR-8600. (100kHz to 2GHz ) They are hardly state-of-the-art receivers but should be capable of detecting jammers driving past. However a new unit is quite pricey $1000 equivalent in the UK as little as $300 for a used version. Also the AMSAT FCD Pro+ USB SDR at $200 and free software. Alan G3NYK - Original Message - From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Monday, October 07, 2013 12:36 PM Subject: Re: [time-nuts] How hard is it to detect a GPS Jammer? Hi Anything that will receive up there should be able to tell you when a jammer comes by. The issue is that not a lot of gear is made for that band (other than GPS receivers). The easy approach would be to use a modern GPS module that puts out noise level / jamming information. Bob On Oct 7, 2013, at 12:59 AM, Hal Murray hmur...@megapathdsl.net wrote: The recent discussion of solar flares screwing up GPS timing was interesting. I just watched Todd Humphreys TED talk again. He's focused on location, but does mention time in terms of stock exchanges. Todd Humphreys: How to fool a GPS http://www.ted.com/talks/todd_humphreys_how_to_fool_a_gps.html He's got a good discussion of GPS jammers and spoofers, but no geeky details. What's the spectral/power output of the typical eBay GPS jammer? Suppose I lived near a major highway. Could I build a receiver that would count jammers driving by? Could I track them (at least somewhat) with a directional antenna on a rotator? Is this something semi-geeky amateurs could contribute to? What sort of gear has harmonics in the GPS band? -- I assume people are familiar with the trucker who jammed the FAA test in NJ. Here is a good story: http://www.insidegnss.com/node/3676 That article has a link to commercial gear targeted at this market. http://www.exelisinc.com/solutions/signalsentry/Pages/default.aspx The graphics shows 3 receivers is a port/harbor setting. -- These are my opinions. I hate spam. ___ 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. ___ 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. ___ 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] How hard is it to detect a GPS Jammer?
Many scanners now go to that frequency e.g AOR AR-8600. (100kHz to 2GHz ) They are hardly state-of-the-art receivers but should be capable of detecting jammers driving past. However a new unit is quite pricey $1000 equivalent in the UK as little as $300 for a used version. Also the AMSAT FCD Pro+ USB SDR at $200 and free software. Alan G3NYK = Or even the DVB-T dongles at just a few pounds (and with a wider bandwidth), covers up to around 1.7 GHz, I have red. For example: UK Europe: https://www.cosycave.co.uk/product.php?id_product=288 US: http://www.nooelec.com/store/software-defined-radio/sdr-receivers/tv28tv2.html#.UlLDKRBE0a4 Admittedly, you aren't supporting AMSAT compared to the FUNcube Pro+, but for a quick experiment 73, David GM8ARV -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] How hard is it to detect a GPS Jammer?
Indeed, the inexpensive DVB-T dongles are showing up in many places including as David noted, decoding GPS. For some details: This gets you to the start of their web site: http://gnss-sdr.org/ This is an interesting document they have published on their project: http://www.cttc.es/wp-content/uploads/2013/09/Turning_TV_into_GNSS_Rx1.pdf The AMSAT Fun Cube Dongle is a very capable and interesting device. Interestingly it uses the same Elonics E4000 front end chip that many of the inexpensive DVB-T devices do. Apparently Elonics is no longer in business and the inexpensive DVB-T devices using this chip are becoming less common. The DVB-T devises using the R820T chip are becoming the preferable versions when those with the E4000 cannot be found. I wonder if the Fun Cube Dongle will be likewise changed (perhaps it already has). Cheers, Graham ve3gtc -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of David J Taylor Sent: October-07-13 10:21 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] How hard is it to detect a GPS Jammer? Many scanners now go to that frequency e.g AOR AR-8600. (100kHz to 2GHz ) They are hardly state-of-the-art receivers but should be capable of detecting jammers driving past. However a new unit is quite pricey $1000 equivalent in the UK as little as $300 for a used version. Also the AMSAT FCD Pro+ USB SDR at $200 and free software. Alan G3NYK = Or even the DVB-T dongles at just a few pounds (and with a wider bandwidth), covers up to around 1.7 GHz, I have red. For example: UK Europe: https://www.cosycave.co.uk/product.php?id_product=288 US: http://www.nooelec.com/store/software-defined-radio/sdr-receivers/tv28tv2.html#.UlLDKRBE0a4 Admittedly, you aren't supporting AMSAT compared to the FUNcube Pro+, but for a quick experiment 73, David GM8ARV -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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. ___ 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] How hard is it to detect a GPS Jammer?
From: Collins, Graham [] I wonder if the Fun Cube Dongle will be likewise changed (perhaps it already has). Cheers, Graham ve3gtc = Yes, Graham, it already has been updated: http://www.funcubedongle.com/?page_id=1073 Adds more filtering and HF coverage, but also has a dead zone between ~240 and 420 MHz. 73, David GM8ARV -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] How hard is it to detect a GPS Jammer?
On 10/7/13 7:46 AM, Collins, Graham wrote: Indeed, the inexpensive DVB-T dongles are showing up in many places including as David noted, decoding GPS. The AMSAT Fun Cube Dongle is a very capable and interesting device. Interestingly it uses the same Elonics E4000 front end chip that many of the inexpensive DVB-T devices do. Apparently Elonics is no longer in business and the inexpensive DVB-T devices using this chip are becoming less common. The DVB-T devises using the R820T chip are becoming the preferable versions when those with the E4000 cannot be found. I wonder if the Fun Cube Dongle will be likewise changed (perhaps it already has). This illustrates is the fundamental problem with leveraging cheap consumer or government surplus gear. The hacker community moves much slower than the commercial one, so you wind up with projects requiring things that are no longer sold. It's particularly endemic in the amateur radio community where we are always repurposing something that hasn't been made for 30 years. But it makes it hard for the new entrant, who doesn't have a box full of old MASTR-II VHF radios or Bell 202 modems or whatever sitting around. But the existence of that gear in some folks's garages tends to ossify the development. How many Bell 202 modems are still in use? But VHF packet radio is 202 compatible, because every product made for the last 30 years was compatible with the 202. Not because it's inherently good, but because you want to be compatible with the other people, and there's a sort of rolling compatibility. (Amateur radio is not the only instance of this. The Scientific Spaceflight community is the same. We love to use spares from previous missions to reduce costs, but that brings along the need to be compatible with the interfaces of those spares. As a result, MIL-STD-1553B Notice 2 or Notice 4 is still used on spacecraft, even if it's not the most appropriate, lowest power, etc.) For a particularly interesting example, look at the plethora of versions of the WRT-54G WiFi router popular with hackers; there's about 50 versions listed on the DD-WRt website. Some of he versions are amenable to dropping in a new OS and/or software, others are not, and still others are modifiable (as in cutting traces, soldering, adding parts and/or connectors) to put in new software. ___ 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] How hard is it to detect a GPS Jammer?
On 10/7/13 8:01 AM, David J Taylor wrote: From: Collins, Graham [] I wonder if the Fun Cube Dongle will be likewise changed (perhaps it already has). Cheers, Graham ve3gtc = Yes, Graham, it already has been updated: http://www.funcubedongle.com/?page_id=1073 Adds more filtering and HF coverage, but also has a dead zone between ~240 and 420 MHz. So much for receiving signals from Transit at 400 MHz (grin) or from Mars (The rovers relay through the orbiters in the 400 MHz band) ___ 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] How hard is it to detect a GPS Jammer?
I think that when a GPS chip reports that there are no satellites found then you got a jammer or a tunnel! At 07-10-2013, you wrote: Hi Anything that will receive up there should be able to tell you when a jammer comes by. The issue is that not a lot of gear is made for that band (other than GPS receivers). The easy approach would be to use a modern GPS module that puts out noise level / jamming information. Bob On Oct 7, 2013, at 12:59 AM, Hal Murray hmur...@megapathdsl.net wrote: The recent discussion of solar flares screwing up GPS timing was interesting. I just watched Todd Humphreys TED talk again. He's focused on location, but ___ 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] How hard is it to detect a GPS Jammer?
Hi Hal: Yes you can detect jammers driving by. There was a prior case of unintentional GPS jamming around Moss Landing harbor, Monterey Bay, California caused by a faulty (oscillating) active TV antenna on a boat that was powered 24/7. Military GPS receivers, like the DAGR or PLGR-II, include jamming detection. http://www.prc68.com/I/DAGR.shtml#P2APPS The patent Handheld GPS jammer locator https://www.google.com/patents/US7233284 Contains some interesting info plus detailed plans for the hardware including mfg model numbers, but not the Altera Model EPM7064STC44-10 FPGA code. I suspect the FPGA not only does what's required for the patent to work, but also some other stuff like switching the LO to other frequencies (maybe both hi and lo side) so that it works not just for L1, but also all the GNSS positioning frequencies. But you could use a micro controller to do the same thing for a one off unit. What was not mentioned in the TED talk was how a US UAV was captured pretty much intact by spoofing a military GPS receiver. Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Hal Murray wrote: The recent discussion of solar flares screwing up GPS timing was interesting. I just watched Todd Humphreys TED talk again. He's focused on location, but does mention time in terms of stock exchanges. Todd Humphreys: How to fool a GPS http://www.ted.com/talks/todd_humphreys_how_to_fool_a_gps.html He's got a good discussion of GPS jammers and spoofers, but no geeky details. What's the spectral/power output of the typical eBay GPS jammer? Suppose I lived near a major highway. Could I build a receiver that would count jammers driving by? Could I track them (at least somewhat) with a directional antenna on a rotator? Is this something semi-geeky amateurs could contribute to? What sort of gear has harmonics in the GPS band? -- I assume people are familiar with the trucker who jammed the FAA test in NJ. Here is a good story: http://www.insidegnss.com/node/3676 That article has a link to commercial gear targeted at this market. http://www.exelisinc.com/solutions/signalsentry/Pages/default.aspx The graphics shows 3 receivers is a port/harbor setting. ___ 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] How hard is it to detect a GPS Jammer?
On spacecraft hardware, even though something is a bit old, it does make sense to use it. Space qualifying a piece of hardware is very, very expensive, because it requires a lot of shake and bake plus thermal vaccuum and other things. Furthermore, there are always unknowns. Do YOU really want to see a Billion dollar mission go wrong, because you used a new, unproven, design of Cammand Receiver or Sequencer? In my view, if you are going into the unknown, you want to use the best available, tested and proven, stuff you can get whereever you can. Remember, many of the launch vehicles still used were made in the 1950s or 1960s, and sat in a missile silo somewhere, as ICBMs for 30+ years. Until fairly recently, the Atlas used sub-mini vacuum tubes. I'm not against inovation, but it's not necessarily about saving a few bucks when older gear is used. YMPV, -John === On 10/7/13 7:46 AM, Collins, Graham wrote: Indeed, the inexpensive DVB-T dongles are showing up in many places including as David noted, decoding GPS. The AMSAT Fun Cube Dongle is a very capable and interesting device. Interestingly it uses the same Elonics E4000 front end chip that many of the inexpensive DVB-T devices do. Apparently Elonics is no longer in business and the inexpensive DVB-T devices using this chip are becoming less common. The DVB-T devises using the R820T chip are becoming the preferable versions when those with the E4000 cannot be found. I wonder if the Fun Cube Dongle will be likewise changed (perhaps it already has). This illustrates is the fundamental problem with leveraging cheap consumer or government surplus gear. The hacker community moves much slower than the commercial one, so you wind up with projects requiring things that are no longer sold. It's particularly endemic in the amateur radio community where we are always repurposing something that hasn't been made for 30 years. But it makes it hard for the new entrant, who doesn't have a box full of old MASTR-II VHF radios or Bell 202 modems or whatever sitting around. But the existence of that gear in some folks's garages tends to ossify the development. How many Bell 202 modems are still in use? But VHF packet radio is 202 compatible, because every product made for the last 30 years was compatible with the 202. Not because it's inherently good, but because you want to be compatible with the other people, and there's a sort of rolling compatibility. (Amateur radio is not the only instance of this. The Scientific Spaceflight community is the same. We love to use spares from previous missions to reduce costs, but that brings along the need to be compatible with the interfaces of those spares. As a result, MIL-STD-1553B Notice 2 or Notice 4 is still used on spacecraft, even if it's not the most appropriate, lowest power, etc.) For a particularly interesting example, look at the plethora of versions of the WRT-54G WiFi router popular with hackers; there's about 50 versions listed on the DD-WRt website. Some of he versions are amenable to dropping in a new OS and/or software, others are not, and still others are modifiable (as in cutting traces, soldering, adding parts and/or connectors) to put in new software. ___ 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. ___ 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] How hard is it to detect a GPS Jammer?
OK so let's say you have a receiver and detect a certain about of power at the right frequency. How do you determine which of three cases you have (1) an actual GPS signal from a satellite. (2) a spoofer (who tries hard to look like #1) or (3) a jammer. You can't just go by the amount of power received because the spoofer/jammer can have any amount of power because they can be at any distance from you and the GPS satellites have variable power because of the distance from the horizon. I think you have to look at the signal itself. You can scan a directional antenna to determine direction but you will get many false positives when real GPS satellites are near the horizon. You would have to track the orbits of all of them. Spoofers are a real problem. A sophisticated spoofer tries very hard to look like the real thing. I think you would have to compare the position, velocity and time you get from GPS with your known position, velocity and time and if there is enough difference assume you are being spoofed. But again a good spoofer will create a subtle error. For example if the spoofer is protecting a building from GPS guided bombs it only needs to create a 200 yard position error. The spoofer may be tracking the location of the falling bomb and may start by transmitting a GPS signal with no error and then add more and more error so as to guide the falling bomb off target. This is actually how the some radar jammers work, they send out a signal designed to be believable so that the guidance system in the anti-air missile dose not detect that it is being jammed an simply goes off target. I think the only way to detect a sophisticated spoof is to have multiple receivers with known relative positions. A change in relative position would indicate a spoofed GPS signal. Jammers can be sophisticated as well the better ones will use a directional antenna aimed at the target and will adjust their power output based on distance to the target. A truck driver likely would not use such a device. A national military might deploy a very sophisticated GPS jammer as part of an air defense system. It would by design be hard to detect. So the easiest thing to detect would be a cheap, GSP jammer that is moving. You could use multiple receivers to triangulate the location and then determine it is not in orbit and is not a reflection from a metal roof or something.The problem is the jammer's very low power. These things are inteneded to only cover a tiny area On Mon, Oct 7, 2013 at 7:46 AM, Collins, Graham coll...@navcanada.cawrote: Indeed, the inexpensive DVB-T dongles are showing up in many places including as David noted, decoding GPS. For some details: This gets you to the start of their web site: http://gnss-sdr.org/ This is an interesting document they have published on their project: http://www.cttc.es/wp-content/uploads/2013/09/Turning_TV_into_GNSS_Rx1.pdf The AMSAT Fun Cube Dongle is a very capable and interesting device. Interestingly it uses the same Elonics E4000 front end chip that many of the inexpensive DVB-T devices do. Apparently Elonics is no longer in business and the inexpensive DVB-T devices using this chip are becoming less common. The DVB-T devises using the R820T chip are becoming the preferable versions when those with the E4000 cannot be found. I wonder if the Fun Cube Dongle will be likewise changed (perhaps it already has). Cheers, Graham ve3gtc -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of David J Taylor Sent: October-07-13 10:21 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] How hard is it to detect a GPS Jammer? Many scanners now go to that frequency e.g AOR AR-8600. (100kHz to 2GHz ) They are hardly state-of-the-art receivers but should be capable of detecting jammers driving past. However a new unit is quite pricey $1000 equivalent in the UK as little as $300 for a used version. Also the AMSAT FCD Pro+ USB SDR at $200 and free software. Alan G3NYK = Or even the DVB-T dongles at just a few pounds (and with a wider bandwidth), covers up to around 1.7 GHz, I have red. For example: UK Europe: https://www.cosycave.co.uk/product.php?id_product=288 US: http://www.nooelec.com/store/software-defined-radio/sdr-receivers/tv28tv2.html#.UlLDKRBE0a4 Admittedly, you aren't supporting AMSAT compared to the FUNcube Pro+, but for a quick experiment 73, David GM8ARV -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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. ___ time-nuts mailing list -- time
Re: [time-nuts] How hard is it to detect a GPS Jammer?
Yes, there is equipment out there today that can be used: UBlox offers jamming detection and level. We incorporated that into the later JLT products, and even made a special board for a customer that displays the GPS spectrum in real time showing the jammers in the frequency domain. Bye, Said Sent From iPhone On Oct 6, 2013, at 21:59, Hal Murray hmur...@megapathdsl.net wrote: The recent discussion of solar flares screwing up GPS timing was interesting. I just watched Todd Humphreys TED talk again. He's focused on location, but does mention time in terms of stock exchanges. Todd Humphreys: How to fool a GPS http://www.ted.com/talks/todd_humphreys_how_to_fool_a_gps.html He's got a good discussion of GPS jammers and spoofers, but no geeky details. What's the spectral/power output of the typical eBay GPS jammer? Suppose I lived near a major highway. Could I build a receiver that would count jammers driving by? Could I track them (at least somewhat) with a directional antenna on a rotator? Is this something semi-geeky amateurs could contribute to? What sort of gear has harmonics in the GPS band? -- I assume people are familiar with the trucker who jammed the FAA test in NJ. Here is a good story: http://www.insidegnss.com/node/3676 That article has a link to commercial gear targeted at this market. http://www.exelisinc.com/solutions/signalsentry/Pages/default.aspx The graphics shows 3 receivers is a port/harbor setting. -- These are my opinions. I hate spam. ___ 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. ___ 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] How hard is it to detect a GPS Jammer?
From: Jim Lux Yes, Graham, it already has been updated: http://www.funcubedongle.com/?page_id=1073 Adds more filtering and HF coverage, but also has a dead zone between ~240 and 420 MHz. So much for receiving signals from Transit at 400 MHz (grin) or from Mars (The rovers relay through the orbiters in the 400 MHz band) == Jim, Just get a FUNcube Dongle Pro (original version) instead! There's a Yahoo group where we often see those sold and bought. Or use one of the DVB-T dongles perhaps with a suitable pre-amp and filter. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] How hard is it to detect a GPS Jammer?
On 10/7/13 10:44 AM, David J Taylor wrote: From: Jim Lux Yes, Graham, it already has been updated: http://www.funcubedongle.com/?page_id=1073 Adds more filtering and HF coverage, but also has a dead zone between ~240 and 420 MHz. So much for receiving signals from Transit at 400 MHz (grin) or from Mars (The rovers relay through the orbiters in the 400 MHz band) == Jim, Just get a FUNcube Dongle Pro (original version) instead! There's a Yahoo group where we often see those sold and bought. Or use one of the DVB-T dongles perhaps with a suitable pre-amp and filter. Cheers, David Well, Transit is dead, as far as I know.. And the last person I know who recorded the UHF signals from Mars used the 100meter antenna at Green Bank. Good to know though.. ___ 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] How hard is it to detect a GPS Jammer?
On 10/7/13 8:31 AM, Chris Albertson wrote: OK so let's say you have a receiver and detect a certain about of power at the right frequency. How do you determine which of three cases you have (1) an actual GPS signal from a satellite. (2) a spoofer (who tries hard to look like #1) or (3) a jammer. The jammers put out many milliwatts and have enormous signals that are obvious on a spectrum analyzer. GPS signals are invisible on a spectrum analyzer, normally. IN fact, most GPS receivers don't work very well if there are signals above the noise floor: they depend on the noise to make them work with their mighty 1 bit quantizers. Spoofers are a real problem. I doubt anyone is selling spoofers on eBay. Sure, one can probably find some code to run on a USRP from some grad student's project. So the easiest thing to detect would be a cheap, GSP jammer that is moving. You could use multiple receivers to triangulate the location and then determine it is not in orbit and is not a reflection from a metal roof or something.The problem is the jammer's very low power. These things are inteneded to only cover a tiny area They are not designed with coverage area in mind. They are basically whatever power the VCO puts out coupled to the antenna From a jamming standpoint, they're not very sophisticated. As a result they dump out something like +10dBm. So running a quick Friis formula link budget, and assuming you want to have a Prec of around -100dBm (10 MHz BW, kTB) 110 = 32+ 20*log10(1575) + 20*log10(d) 110-32 - 25 = 20*log10(d) d = 400 km... This is why they are such a problem ___ 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] How hard is it to detect a GPS Jammer?
On Mon, Oct 07, 2013 at 08:02:13AM -0700, Jim Lux wrote: On 10/7/13 7:46 AM, Collins, Graham wrote: The AMSAT Fun Cube Dongle is a very capable and interesting device. Interestingly it uses the same Elonics E4000 front end chip that many of the inexpensive DVB-T devices do. Apparently Elonics is no longer in business and the inexpensive DVB-T devices using this chip are becoming less common. The DVB-T devises using the R820T chip are becoming the preferable versions when those with the E4000 cannot be found. I wonder if the Fun Cube Dongle will be likewise changed (perhaps it already has). This illustrates is the fundamental problem with leveraging cheap consumer or government surplus gear. The hacker community moves much slower than the commercial one, so you wind up with projects requiring things that are no longer sold. It's particularly endemic in the amateur radio community where we are always repurposing something that hasn't been made for 30 years. But it makes it hard for the new entrant, who doesn't have a box full of old MASTR-II VHF radios or Bell 202 modems or whatever sitting around. This is also rather a sin of the marketing driven innovation economy - product life cycles are so terribly short that by the time someone spots a device that can be re-purposed in an interesting way it is usually already EOL and unavailable in traditional new product channels. It takes time to do the reverse engineering (schematics, source code, FPGA VHDL - what is that and why should we give it to you ?) and time to figure out how to re-purpose and make the thing work and usually this is part time and one or two people and not a whole staff. And then there is time to write it up and publish articles and plans, and time for folks to try it and discover it works... But as many on this list know all too well, even in reasonably well funded new product development the old story is hey that is a really neat chip that does just what I need only to hear Sorry too low demand, or design or production problems, or ROHS or something, not available in the future - or maybe just vaporware to assess interest and never really available. Or you design it in, the company is bought by someone else, the chip abandoned and now YOUR product is EOL early. But the existence of that gear in some folks's garages tends to ossify the development. How many Bell 202 modems are still in use? But VHF packet radio is 202 compatible, because every product made for the last 30 years was compatible with the 202. Not because it's inherently good, but because you want to be compatible with the other people, and there's a sort of rolling compatibility. But that is not all bad, if you just need a modem that works. Choosing something state of the art that DID NOT become a major defacto standard (and there are dozens of examples in the modem world alone) means you only can expect to use the original device and maybe one or two subsequent versions before it becomes unavailable and completely obscure and rare and totally incompatible. And then your design has to be incompatibly upgraded with no backwards interoperability support where if you had used some moldy oldy but goody you probably could buy modern DSP based hardware that does that standard (you can for 202s) among many other useful ones...and support both higher performance and backwards compatibility modes at low cost and with high performance. Obviously the problem then becomes convincing enough old pharte holdouts to upgrade when it truly becomes a nightmare to support the old. And that is not always easy. -- Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, Mass 02493 An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either. ___ 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] How hard is it to detect a GPS Jammer?
Yes, these specific jammers do, but someone asked the general question how to detect a jammer and a sophisticated jammer will use no more power than is requires so as to avoid detection. Could it be that there are such devices and they are successful at avoiding detection?Likely not as at present no one cares if they are detected. But if they start getting hunted out things will change. About spoofers, yes thay are not available on eBay. But I was thinking about military applications. Can you know when you are being spoofed? On Mon, Oct 7, 2013 at 6:11 PM, Jim Lux jim...@earthlink.net wrote: The jammers put out many milliwatts and have enormous signals that are obvious on a spectrum analyzer. GPS signals are invisible on a spectrum analyzer, normally. IN fact, most GPS receivers don't work very well if there are signals above the noise floor: they depend on the noise to make them work with their mighty 1 bit quantizers. Spoofers are a real problem. I doubt anyone is selling spoofers on eBay. Sure, one can probably find some code to run on a USRP from some grad student's project. -- Chris Albertson Redondo Beach, California ___ 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] How hard is it to detect a GPS Jammer?
In general, we expect a jammer to be involved in criminal activity. What about a wilderness guide whose reputation is built on finding the best spots to view Nature's wonders. Should he or she be happy to let people in the guided group save the coordinates of those spots in order to compete with the guide or avoid guide's services in the future? Or would that be a justifiable use of jamming? Hypothetically speaking, of course. Bill Hawkins ___ 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] How hard is it to detect a GPS Jammer?
On 10/7/13 9:30 PM, Bill Hawkins wrote: In general, we expect a jammer to be involved in criminal activity. What about a wilderness guide whose reputation is built on finding the best spots to view Nature's wonders. Should he or she be happy to let people in the guided group save the coordinates of those spots in order to compete with the guide or avoid guide's services in the future? or the favorite fishing hole.. Way back when, one of the applications of frequency hopping radios was for fishermen (ocean) so that they couldn't be DFed. They had already done the scrambler thing. Or would that be a justifiable use of jamming? No. It's that same moral thing.. Should you allow cellphone jammers in movie theaters? In my mind, these are all hacks to solve a more fundamental social question about appropriate use. cellphone jammers are a sort of passive aggressive way for a business owner to not have to confront paying customers about their misuse of cellphones. At the Athaeneum, the faculty club at CalTech, cellphone use is not permitted. Pull out a cellphone, and the staff politely tells you Sir, we would prefer you not use that here, would you like to step outside. At the Austin Drafthouse theater, they're a bit more confrontational. Anyone can buy a chainsaw or sledge hammer. There is potential for misuse, but common decency mitigates against those uses. Hypothetically speaking, of course. Bill Hawkins ___ 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. ___ 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] How hard is it to detect a GPS Jammer?
On Mon, Oct 07, 2013 at 11:30:57PM -0500, Bill Hawkins wrote: In general, we expect a jammer to be involved in criminal activity. What about a wilderness guide whose reputation is built on finding the best spots to view Nature's wonders. Should he or she be happy to let people in the guided group save the coordinates of those spots in order to compete with the guide or avoid guide's services in the future? Or would that be a justifiable use of jamming? No. Jamming can potentially impact a much wider area and safety of life critical uses of GPS, and very few wilderness guides are expert enough to understand, control and mitigate this risk. And even if one particular one was, how is this to be reliably ensured ? Should he or she be licensed and certified and regulated as to how and when he might jam safely - we don't current issue GPS denial licenses (except maybe to LightSquared) ? And even with someone suitably trained and licensed and certified there is a balance between the slight risk that his jamming harm something important or critical that society relies upon and his own personal interest in denying GPS to his customers that I am not sure we as a society have quite figured out. Should private businesses be allowed to deny GPS (or for that matter cellphone access) to folks nearby or their customers - is this a legitimate interference with a public resource ? Obviously if the answer is yes, businesses should be allowed to jam cellphones or GPS - then what are the limits - eventually all those private jammers will make such services MUCH less useful - as they will be unpredictably unreliable at apparently random times and places which makes it very hard to trust them for anything important. We will in other words have allowed the private interests of certain folks to destroy a commons, something we are getting increasingly good at BTW. I suppose it is SOMEWHAT justified for a guide to search his customers for GPSes, or have a strict policy of dropping them off at the nearest road if they are found to be using one, or even to use a GPS detector to ID GPSes in use... but an active attack seems wrong given the risks involved. And anything more nuanced in a policy on such invites various low life scumbags to push the limits and use blatantly excessive power, dangerous antenna locations, and generally horrid engineering that puts important uses and users of the technology at serious risk for very selfish personal reasons - perhaps in some cases just buying some cheapo jammer instead of a proper licensed and limited one managed and installed by someone who knows what he is doing. Finally of course, who is to say that I cannot use my cellphone for important messages - perhaps life critical (my wife is a doctor and does this from time to time when she is on call)... or my GPS to locate a store somewhere... perhaps if the jamming ONLY worked in a completely private space owned or controlled by the jammer and not at all outside of it would this begin to be marginally acceptable but it certainly isn't in public spaces. And I believe there should be mandatory readily visible notices saying that jamming is use... allowing someone who truly needs access to know what is happening. As for the wilderness case specifically there are any number of strategies to defeat short range jamming of that sort - just announce you have to go as the group leaves the scenic knoll and go back and take a bearing (maybe automatically from a concealed GPS you already have in you backpack) while peeing on the special rock... Inverse square law applies here of course... hard to radiate enough power to deny over a long enough distance without being completely unsafe for other users. -- Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, Mass 02493 An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either. ___ 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.
