“GPS testing”…or do they mean jamming?

Ben Ellison

Ben Ellison

Panbo editor, publisher & chief bottlewasher from 4/2005 until 8/2018, and now pleased to have Ben Stein as a very able publisher, webmaster, and editing colleague. Please don't regard him as an "expert"; he's getting quite old and thinks that "fadiddling fumble-putz" is a more accurate description.

39 Responses

  1. Ben Ellison Ben Ellison says:

    PS. Thanks to our friend Dan Corcoran for tipping me on the FAA Advisory, and to Henry Marx of Landfall Navigation for letting me know about the jammers-in-Jersey story.

  2. Bob Mueller says:

    Yes the U.S. was foolish to destroy LORAN. It was a great redundancy to GPS and much more difficult to jam. I am curious: how many Panbots can use a sextant? Although not practical for me to use for serious navigation where I cruise on inland lakes, it was very much fun to learn how to use the nav “gadget” of previous generations.

  3. John - gCaptain says:

    “Was the U.S. foolish to kill Loran and eLoran?”
    Umm…. YES!

  4. Jim Hebert Jim Hebert says:

    I suspect that the jamming involves interfering with reception of the L1 carrier frequency of the system. The L1 carrier is at 1575.42-MHz. If the source of the interfering signal is at or near sea level, the signal should be able to propagate only to the usual radio horizon, perhaps just a few miles. Aircraft at high altitude will be in line-of-sight of the source for much greater distances.
    With a height of 40,000 feet, an aircraft’s radio horizon distance would be
    d = 1.42 X h^0.5 where d is in miles and h is in feet.
    d = 1.42 x (40,000)^0.5
    d = 284-miles
    Since the warning refers to a range of 370-nautical-miles for aircraft at 40,000-feet, we may have to assume the source of the interference will also have some altitude. It would need to have a radio horizon of [(370×1.15)-284] miles or 141-miles. Solving for h
    h = (d/1.42)^2
    h = (141/1.42)^2
    h=9,860 feet
    We could surmise that the source of the interference will be from an aircraft operating about 10,000-feet.

  5. Jim Hebert Jim Hebert says:

    I also think the destruction of the LORAN system was a bad decision. There was solid engineering and reasoning to support LORAN with eLORAN enhancement as a back-up system.
    The decision to destroy the LORAN system appeared to me to be quite political. I’ll leave my political opinions about the decision unsaid; that sort of discussion never goes very far in a technical blog.

  6. Donald Joyce says:

    Your presentation indicates that all surface receivers within the jammer’s radius of 141 miles would be impacted. There is quite a lot of commercial traffic of the Florida/ Georgia line consisting of tugs/barges and fishing vessels, to say nothing of the tankers/container ships entering nearby harbors.
    Any thoughts on how one prevents impacting them?

  7. Ben Ellison Ben Ellison says:

    Thanks, Jim! Though now I feel a little dumb that I couldn’t visualize the area of interference as where the jamming signals intersect with the GPS signals. However, I’m going to guess that the jamming source is on a ship, and that’s why there aren’t any warnings (I can find) about GPS problems at sea level. That doesn’t mean that your math is wrong, but it may be that the FAA went with very generous ranges of possibility so as not to surprise anyone?
    At any rate, Jeff and Karen Siegel are shifting down to the mid South Carolina coast this weekend, and Jeff says he’ll monitor his GPS during the testing periods. According to the Advisory, a NOTAM will be published at least 24 hours before actual tests. I found the NOTAMs site, but nothing about a test, at least for ATL. Maybe someone understands the system better:

  8. Bob Etter says:

    LNTM for that area also notes GPS “testing”. It is fairly common there.

  9. Ben Ellison Ben Ellison says:

    Thanks, Bob! This warning seems to confirm Jim’s surmise of 141 mile range quite nicely. I’m surprised they’re not making a bigger deal of it if it really can mess up GPS sensors in that large circle.

  10. Bob Etter says:

    While I haven’t been down thataway for 2 years now, I used to take the boat to Florida every winter…for 3 years running there was notice that some GPS anomaly would exist, generally just North of the Straits and usually centered on Cape Canaveral. I never noticed any impact GPS-wise but as I was closing the coast at that point, “Old School” piloting was as much in use as GPS.

  11. Bob Mueller says:

    Too bad those coordinates are not in the Bermuda Triangle. That would really get people talking!

  12. Dan Corcoran (b393capt) says:

    I would think instead it is ship based, and someone has simply added 100 or more miles additional safety margin at every altitude, including sea level, onto what the laws of physics would already give as a worst case.

  13. Mitch says:

    There are two separate warnings for BOTH coasts. Check out the FAA Public Notice site for their warning of 1/19 and 1/14 – the website can be found here:

  14. Ben Ellison Ben Ellison says:

    Thanks, Mitch! The West Coast test looks similar in terms of ranges, but its duration is shorter and the epicenter is on land…out in the desert, I think, but close to the route between LA and Vegas. That could be interesting 😉

  15. Jim Hebert Jim Hebert says:

    The notice for testing in California gives the LAT/LON as 355632N/1173458W
    If you look on GOOGLE EARTH at
    35 55.63 N, 117 37.55 W
    you will see a structure that appears to be either a drive-in movie screen, or perhaps some sort of large RADAR antenna array.

  16. Raul says:

    I believe that this lies within the the China Lake Naval Weapons Center restricted area. I used to do a lot of dirt bike riding north of this point and often would see pretty interesting aircraft flying around.

  17. Sandy Daugherty says:

    Our opinions on LORAN termination are as meaningful as gorilla poo. There is no putting it back.

  18. Anonymous says:

    This is all pretty normal stuff, see the link below:

  19. Jim Hebert Jim Hebert says:

    “Our opinions on LORAN termination are as meaningful as gorilla poo.”
    For people who think like that, that statement is true.

  20. Sandy Daugherty says:

    Thank you, Jim, for Continuous Wave, and the Northern Channel guide. It significantly enhanced a recent trip there, a truly wonderful place to sail.

  21. steverow says:

    This sort of thing happens intermittently here also.
    Usually it is confined to the North or NE of Scotland, basically because to do it in the south with the extremely busy shipping lanes would bring almost certain disaster of some sort, collisions etc etc.
    Anyone with more than two brain cells privately recognises that it is some form of EWF countermeasures under test, either Airborne or Vessel based, by UK US or another Nato power, or simply just a routine EWFC exercise or whatever. It has to be done, in case we need it for real guys. Time to get out the paper and compass, and brush up on those running fixes when it happens.

  22. Ben Ellison Ben Ellison says:

    Well, I stand confused. Is it just that warnings about potential GPS unreliability are “normal” or that actual GPS unreliability when warned is “normal”? I know there are various warnings like these two recent ones on the U.S. southeast and southwest coasts, but I think we’d hear about it if many regular GPS users in cars, planes, and boats were running into real problems.

  23. Arnold says:

    If you look on GOOGLE EARTH at
    35 55.63 N, 117 37.55 W
    Doh! no Google streetview available yet…

  24. SanderO says:

    This may be a bit political… but who “owns” the GPS system and owned the now defunct Loran system?
    The taxpayers paid for it and fund its maintenance.
    It is used for commercial navigation as well as military uses.
    So who gets to “control” these systems? And how are these decisions made?

  25. Sandy Daugherty says:

    For whatever motives, good or bad, scientific or political, Loran is dead. We may prefer to think it was murder, euthanasia, or kindness, but crying over spilt milk just prolongs the clean up.
    What does it accomplish to complain that we were unable to prevail when the decision was made? De we think that It can be restored? At what cost?
    Look forward. Where there is a need, technology finds a way. In fact, technology finds a way where there is no apparent need, and creates one! Look forward to the day that GPS is due for replacement; look for the next technology. How will we navigate ten years from now, or twenty?
    Lets not dwell on our tactical loses. Loran has gone the way of bonfire navigation for airmail routes, ADF approaches, and Omega navigation. While there will always be whiskered old salts fondling their sextants, WE should be scanning the scientific horizons for the next sunrise.

  26. John Hinckley says:

    Speaking of “GPS Testing”, I ran across these pages (with documents to d/l), from Agilent Instruments on GPS testing; some information more oriented towards their products, and some more “white papers”. A lot rather dense, and somewhat more oriented towards land gps devices, but some tidbits here and there.
    See following links:
    John Hinckley

  27. Dan Corcoran (b393capt) says:

    Sandy, Dead? “euthanasia or kindness”, you jest, yes? Ben wrote such a good explination of how valuable eLoran is.
    Hot on the heals of international commitments to eLoran, the USCG recognized that in eLoran they had a new born baby that needed nurturing (funding) by other agencies that would have been more suitable parents (electric grid syncronization/timing, wireless data communications syncronization, crytography, air traffic control modernization, etc.).
    Who would have guessed that rather than being accepted for adoption, this new born baby would be kicked to the curb as if Loran was a 98 yr old geezer unreasonably requesting a heart transplant while a 50 yr old drug addict was on the operating table and needed it more? After all, with the government growing at 24% over two years, why not fund eLoran also?
    Maybe because … if GPS & eLoran are used together, its harder to effectively “test”/jam GPS ?

  28. Ben Ellison Ben Ellison says:

    Thanks, Dan, but I tend to agree with Sandy that eLoran died along with Loran in the U.S., and I’ve heard nothing about a resurrection. It sure seemed like a dumb move to me, but I doubt it was done for nefarious reasons. The questions now are when will a real backup appear, and will there be some sort of major outage in the meantime.
    There may be something of interest here, if you can cut through the beauacratize:
    SanderO, check the organizational chart for a partial answer to the question who runs GPS. I say partial because I think our government is an expression of us whether we like what it does or not.

  29. Ben Ellison Ben Ellison says:

    Thanks, Dan, but I tend to agree with Sandy that eLoran died along with Loran in the U.S., and I’ve heard nothing about a resurrection. It sure seemed like a dumb move to me, but I doubt it was done for nefarious reasons. The questions now are when will a real backup appear, and will there be some sort of major outage in the meantime.
    There may be something of interest here, if you can cut through the beauacratize:
    SanderO, check the organizational chart for a partial answer to the question who runs GPS. I say partial because I think our government is an expression of us whether we like what it does or not.

  30. Dan Corcoran (b393capt) says:

    Interesting excerpt from: http://www.pnt.gov/
    “the Department of Defense is making prudent investments in alternative PNT technologies to supplement GPS in times when satellite services are unavailable.” — what do you think this could be ?

  31. Sandy Daugherty says:

    What an interesting site! Dan’s quote could be read to mean the Air Force is fronting some money for research outside DOD. While that should involve DARPA, it could also mean direct dealings with other reasearch and development entities outside the US.

  32. Donald Joyce says:

    The DOD routinely funds research performed by entities outside of the DOD as well as outside the US and has done so for a long long time with great success. DARPA represents a small fraction of the overall DOD research budget.

  33. Jeffrey Siegel says:

    I’m sitting at a marina on the coast of South Carolina in the inner zone. Been running an anchor alarm while tied up to the dock for a couple of nights now. Makes me feel sort of foolish – even worse, I’m using multiple alarms with very tight tolerances. So far, no alarms have gone off…

  34. Bob Etter says:

    Latest LNTM for District Seven with the GPS testing notices AND some interesting AIS testing in Govt Cut on pages 4/5
    Looks like both the USCG and the Navy are very busy this week. My take on this is that the GPS sky is NOT falling, these activities are well documented and a lot of the buzz on some other sites is perhaps a bit over-blown.

  35. Ben Ellison Ben Ellison says:

    Yipe! The email comment that came with this link reads, “The FCC has gone completely and utterly *MAD*”

  36. Derek says:

    Interesting reading on Lightsquared boss Philip A. Falcone

  37. JoeH says:

    Much of the spectrum Lightsquared is using in their broadband buildout has been leased from Inmarsat, and consequently there will be an impact to users of maritime and aeronautical Inmarsat terminals operating near these Lightsquared towers. We don’t yet know how great that impact will be; Inmarsat is doing tests now. The FCC did require Lightsquared give the Coast Guard six months notification of areas where maritime terminals could be affected. Since Lightsquared has to have at least part of their system operating by Feb 2012, we should have some idea in August. However, it may not be possible to test legacy Inmarsat equipment still in use, so we won’t know the impact for sure until the systems goes operational.
    Question: how much do mariners rely on Inmarsat when in cell range of shore? If not much, then that aspect of this Lightsquared buildout might not be too big a problem.

  38. TimT says:

    There’s some interesting stuff on the effects of GPS jamming done by the GLA – see http://www.gla-rrnav.org/radionavigation/gnss_dgnss/vulnerabilities.html
    Of course the same vulnerabilities apply to Glonass, Galileo, Compass etc as they come into use, so lose one, lose them all. This is a big vulnerability, and many countries are concerned about this.
    eLoran overcomes these problems, and looks likely to be rolled out across Europe, plus possibly Russia, Japan and the Gulf as follow-ons. The alternative is “hardened” GPS, but the GLA’s cost-benefit analysis showed this to be more expensive and not as good. I believe that there are still those in the US govt promoting eLoran.
    The Lightsquared issue will affect all GPS users, as the frequency they will use is part of the GPS frequency band. Inmarsat have this capability on their satellites for EGNOS in Europe (not sure if they are used for WAAS in the USA). It won’t affect users of Inmarsat voice/data comms, as these are on a different frequency.

  39. Anon Sailor says:

    Ben – the dates/location of this outage coincide with the final pre-deployment exercises of the USS George H.W. Bush Carrier Strike Group. Part of the exercise involves training to ships and aircraft to fight in a “GPS denied” environment. In my experience, the NOTAMS/NOTMARS greatly exaggerate the impacts of this “testing” in a big CYA kind of way.
    Did anyone along the ICW experience any troubles? I would be really surprised if they did.

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