GPS Doesn't Fail

For once, Bugs might be onto something...

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I see NOTAMS for satellite outages all the time
 
Anyone notice the 50 ft is where the greatset influx of border crossings are?
 
The GPS isn't failing, it's being purposefully sabotaged by agents of the federal govt. If you don't know the diff, well that's a completely different discussion.
 
I think it borders on unacceptable that the govt. has so many of these outages. Seriously, why do they need to "test" whatever they're testing over and over again while interfering with what has become a vital service....?

At least do it at 3am, or over uninhabited ocean or something.
 
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Let's see... what is the backup for ADS-B...

M1 eyeball ...
 
I am planning to fly over El Paso heading west on Nov. 1. I will let you know if I end up in Mexico!!!:)
 
denverpilot said:
I can't find the thread with the "GPS Doesn't Fail" garbage this morning, but just thought I'd pass this along for posterity...

Note the length of time and the area affected.

https://www.faasafety.gov/files/notices/2014/Sep/WSMR_14-09_GPS_Flight_Advisory.pdf

We get one of these notices monthly around here, at least.

YMMV.
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I plugged the coordinates into Google Maps (assuming format is ddd.hh.mm.ss) and found Holloman AFB very close to the center. Turns our they are a dedicated GPS messer-upper:

http://www.holloman.af.mil/library/factsheets/factsheet_print.asp?fsID=5922&page=1

The 746th Test Squadron (TS), also known as the Central Inertial and GPS Test Facility (CIGTF), is the DoD's designated lead test organization chartered to test and evaluate Global Positioning System (GPS) user equipment (UE) and integrated GPS based guidance and navigation systems. To this end, the 746 TS manages the tri-service GPS Test Center of Expertise (COE) comprised of Army, Navy, and Air Force test agencies chartered to support GPS test and evaluation initiatives. With over 40 years of experience, CIGTF has established itself as a leader in Inertial, GPS, and blended GPS/Inertial component and system testing. In addition, CIGTF's inclusive ground, field, and flight-testing capabilities offer the customer a cost-effective means to evaluate their guidance and navigation systems.

Handy Customer Handbook of their services:
http://www.dtic.mil/dtic/tr/fulltext/u2/a471913.pdf
 
dans2992 said:
I think it borders on unacceptable that the govt. has so many of these outages. Seriously, why do they need to "test" whatever they're testing over and over again while interfering with what has become a vital service....?

At least do it at 3am, or over uninhabited ocean or something.
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The Air Force (and other armed forces) still view GPS as a military system that the rest of the world is mooching. They're probably testing to see how well their new receivers work in an area of jamming.

GPS III is supposed to have a safety of life signal (L5) that the Air Force will guarantee will not be tampered with.
 
COFlyBoy said:
The Air Force (and other armed forces) still view GPS as a military system that the rest of the world is mooching. They're probably testing to see how well their new receivers work in an area of jamming.

GPS III is supposed to have a safety of life signal (L5) that the Air Force will guarantee will not be tampered with.
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So, if they'll be an "untampered" signal, what would be the point of messing with the signal in the first place.

Note that if you have an iPhone/iPad with internal GPS, you can just use GLONASS instead. It seems to work during GPS outages.
 
dans2992 said:
So, if they'll be an "untampered" signal, what would be the point of messing with the signal in the first place.

Note that if you have an iPhone/iPad with internal GPS, you can just use GLONASS instead. It seems to work during GPS outages.
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haha remember the first nonaviation GPS handhelds had software that shut them off at 100 mph...
 
I will let you know if I end up in Mexico!!!:)
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Uh, probably not, Scott. If you are in Mexico, you will probably be in jail somewhere :).
 
Good thing they shut down LORAN, isn't it?
 
docmirror said:
The GPS isn't failing, it's being purposefully sabotaged by agents of the federal govt. If you don't know the diff, well that's a completely different discussion.
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Sorry Doc, you're probably wrong on this one.

There's a large GPS test facility in Alamagordo that simulates a full GPS cluster inside a big building built as a Farraday cage.

While this *particular* announcement may or may not be intentional jamming, it's centered on the building.

They've been issuing NOTAMs during large scale vendor interop tests in that building for many years. A friend was there a couple of years ago for interop testing of various APCO Project 25 radio systems that all had GPS capabilities.

Big room. Bunch of vendors standing around, mostly waiting for extremely detailed test results as the techs "mess with" the simulated GPS satellite cluster.

He mentioned that two vendor's receiver chipsets in particular would remain in a "gps signal ok" status and provide accurate readings many many dB of noise below everyone else's. All the other chipsets gave up and unlocked.

He shared who, but the tests are secret so I'm not saying.

Let's just say, stick with the big name brands if you want a receiver that'll pull out signals when you're in sub-basement 3 and your dispatcher is sending help.

OTOH, both Raytheon and someone else are both doing field trials of wide area jammers also. Raytheon's tests were in the Southeast south of Georgia.

The other company (I forget - Army contract - truck-based) used the area southeast of Colorado Springs. We had NOTAMs on that one, too. Haven't seen any more of those NOTAMs for a while now.

Anyway, point is, sometimes they're worried about the effects of testing leaking out of the NM test building and not meaning for it to intentionally do so.

Gotta test somewhere.

I don't think it has much to do with the border. But hell, maybe. Fire up the "test lab" giant cover story anytime you want to confuse the mules leading the group's?

Pretty far fetched. But certainly not beyond the stupidity of our government.
 
Jim Logajan said:
I plugged the coordinates into Google Maps (assuming format is ddd.hh.mm.ss) and found Holloman AFB very close to the center. Turns our they are a dedicated GPS messer-upper:

http://www.holloman.af.mil/library/factsheets/factsheet_print.asp?fsID=5922&page=1

The 746th Test Squadron (TS), also known as the Central Inertial and GPS Test Facility (CIGTF), is the DoD's designated lead test organization chartered to test and evaluate Global Positioning System (GPS) user equipment (UE) and integrated GPS based guidance and navigation systems. To this end, the 746 TS manages the tri-service GPS Test Center of Expertise (COE) comprised of Army, Navy, and Air Force test agencies chartered to support GPS test and evaluation initiatives. With over 40 years of experience, CIGTF has established itself as a leader in Inertial, GPS, and blended GPS/Inertial component and system testing. In addition, CIGTF's inclusive ground, field, and flight-testing capabilities offer the customer a cost-effective means to evaluate their guidance and navigation systems.

Handy Customer Handbook of their services:
http://www.dtic.mil/dtic/tr/fulltext/u2/a471913.pdf
Click to expand...


There you go. Now find photos of the test lab. They're pretty nifty. It's not a big secret.
 
denverpilot said:
Sorry Doc, you're probably wrong on this one.
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Well, lets review(I used to do testing like this on systems).

1. The GPS is not "failing".
2. It is indeed intentional.
3. Being conducted by people associated with the govt.
4. The actions are intended to disrupt, and/or distort GPS signals which is a form of sabotage - hence the need for a notam.

I will stick with my original statement. It is correct.
 
So they issue these notams even when testing in the "faraday cage" of a building?
 
brian];1568932 said:
Let's see... what is the backup for ADS-B...

M1 eyeball ...
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M1 eyeball still required, even when ADS-B is working. When ADS-B fails, the backup consists of primary and secondary radar, this is part of the reason you have to keep your transponder. Throughput may degrade, but safety is not affected in an outage.
 
I will say that since I added partial ADS-B traffic capability, I am a lot more diligent about using the M1 Eyeball. Even with the limited display capability, it has reinforced the need to look outside. Couple of examples:

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I've had my GPS take a dump mid-flight. Non event really. I was following along on a chart, just maintained my heading and used pilotage. If I felt that lost I'd have called up a radar facility and gotten vectors.
 
docmirror said:
Well, lets review(I used to do testing like this on systems).



1. The GPS is not "failing".

2. It is indeed intentional.

3. Being conducted by people associated with the govt.

4. The actions are intended to disrupt, and/or distort GPS signals which is a form of sabotage - hence the need for a notam.



I will stick with my original statement. It is correct.
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Not ever intentional to allow RF to leak out of the test facility.

dans2992 said:
So they issue these notams even when testing in the "faraday cage" of a building?
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Yes.
 
Given the ubiquity of solid-state gyros and accelerometers in every phone and tablet, it seems like it would not be hard to come up with a solid-state inertial nav device that could talk to a GPS to keep itself updated, and then take over navigation if the GPS signal becomes lost.

The system would probably degrade in accuracy over time, but it should be close enough for long enough to complete most flights.
 
dans2992 said:
They're really "crying wolf" then.
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Not really. Any engineer who is familiar with RF knows that there is no such thing as perfect shielding, and even if there were, there is always Murphy's Law.
 
Bottling RF is pretty much impossible. Why do you think they issue the notam?

duh...
 
Those NOTAMs are constant around here. Something to do with alien abductions/anal probing around Roswell. But if you have a TSO 146 navigator it will let you know if GPS integrity is lost.

I have never had a loss of GPS position integrity, but it could happen. They have tomissue those NOTAMs any time their testing even has the possibility to interfere with GPS integrity. It doesn't necessarily mean the signal definitely will be lost.
 
Palmpilot said:
Not really. Any engineer who is familiar with RF knows that there is no such thing as perfect shielding, and even if there were, there is always Murphy's Law.
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Edsel Murphy is my patron saint. As an EMC engineer I depend on things going wrong to stay employed. :D

docmirror said:
Bottling RF is pretty much impossible. Why do you think they issue the notam?

duh...
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Not really, but the question is - how much RF can you tolerate leaking out? And how much are you willing to spend to contain it? I can work with MEs to come up with a box that won't leak RF, but it won't be cheap and you sure as heck won't want to mass produce them. We built a few that way when I worked in aerospace over 30 years ago, but we don't even consider it in the computer world.

Now, that Faraday cage (shielded room) that they are using has failure modes that won't necessarily be obvious to the users when they occur, but if they occur while the jamming transmitters are active people using GPS equipment outside the chamber may very well be made aware of the problem. Hence the NOTAM. A cautious approach.
 
dans2992 said:
So they issue these notams even when testing in the "faraday cage" of a building?
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Faraday cage? May not be one. There is this claim on the Holloman AFB page (I've underlined the part that seems to imply no cages may be used in some of their tests):

Antenna Test Range

  • Conducts multi-element GPS antenna testing using multiple jammers in a controlled, open-air environment
  • Covers the middle ground between laboratory and flight test capabilities and offers an additional environment to satisfy customer test requirements
 
Jim Logajan said:
Faraday cage? May not be one. There is this claim on the Holloman AFB page (I've underlined the part that seems to imply no cages may be used in some of their tests):

Antenna Test Range

  • Conducts multi-element GPS antenna testing using multiple jammers in a controlled, open-air environment
  • Covers the middle ground between laboratory and flight test capabilities and offers an additional environment to satisfy customer test requirements
Click to expand...

:rofl::rofl::rofl::rofl::rofl::rofl::rofl:

No,,, we have been reliably informed that the notam is 'just in case', that the testing isn't going to cause any problems with GPS signal.

Sure - yup - trust us, we're from the govt and we are here to help. :lol:
 
Ghery said:
Edsel Murphy is my patron saint. As an EMC engineer I depend on things going wrong to stay employed. :D



Not really, but the question is - how much RF can you tolerate leaking out? And how much are you willing to spend to contain it? I can work with MEs to come up with a box that won't leak RF, but it won't be cheap and you sure as heck won't want to mass produce them. We built a few that way when I worked in aerospace over 30 years ago, but we don't even consider it in the computer world.

Now, that Faraday cage (shielded room) that they are using has failure modes that won't necessarily be obvious to the users when they occur, but if they occur while the jamming transmitters are active people using GPS equipment outside the chamber may very well be made aware of the problem. Hence the NOTAM. A cautious approach.
Click to expand...

In addition to the problems involved with making doors etc. RF-tight, I was thinking about the equation for skin effect, which seems to imply that no matter how thick the sheet metal, in the absence of a perfect conductor, there will always be some trace of RF current on the outside. However, I'm not sure what happens when it gets down to the level where quantum effects become important.

Regarding working with mechanical engineers, I have found that one sometimes has to explain to them that slots can make dandy antennas under the right conditions. :)
 
Palmpilot said:
In addition to the problems involved with making doors etc. RF-tight, I was thinking about the equation for skin effect, which seems to imply that no matter how thick the sheet metal, in the absence of a perfect conductor, there will always be some trace of RF current on the outside. However, I'm not sure what happens when it gets down to the level where quantum effects become important.

Regarding working with mechanical engineers, I have found that one sometimes has to explain to them that slots can make dandy antennas under the right conditions. :)
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While the sheet metal may not be perfect, it typically is "close enough for government work". 100 dB isn't hard to obtain at all. Heck, our modular rooms at work give us that (or did the last time they were tested).

Sometimes those MEs make fantastic antennas without even trying. :D
 
dans2992 said:
So, if they'll be an "untampered" signal, what would be the point of messing with the signal in the first place.
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Because the govt still owns it and therefore can always shut it off when national security requires it.

Same with the Differential GPS that was created back when we intentionally scrambled GPS signal to reduce accuracy for non-military users.
 
My GPSMap 296 lost signal for the last ten or fifteen minutes of flight yesterday. I fiddled with antenna placement and flexed the cable to look for a bad connection, but no luck. After landing, I regained signal by cycling the power.
 
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