GPS Loss Theory

Sinistar

Sinistar

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Brad
Okay, during a flight with @WannFly about a month ago we both lost GPS at the same time and our planes were maybe 3-4 miles apart.

On my recent trip out to KRAP and back I also lost GPS.

Both cases had one thing in common: Being fairly close to ADSB Ground Based Transmitters.

Could there be something about them, perhaps the ones for the higher altitudes that are somehow interfering with the GPS satellite signals?

Or maybe its the receiving circuitry on the ADSB In devices.

I have a Garmin GDL39 and @WannFly has a GDL50. So different devices but same vendor, same outage.
 
Actually, I lost GPS (G430) in my club's Skyhawk twice a few months ago, both times near ADS-B ground stations. It came back pretty quickly, maybe around 5-10 minutes? I haven't had any issues in any other similarly equipped aircraft though. So maybe the ADS-B ground stations are just a coincidence?
 
I wouldn't think an ADSB ground station would interfere with GPS, the frequencies used aren't that close together. If it happens in the future you may want to check https://sapt.faa.gov/default.php or applicable NOTAMS to see if there would have been an issue during your flight...
 
Maybe there is a "dirty" transmitter causing interference. We had one here this summer. We were picking up sporadic music on both CTAF and our local Center frequency for days. You only got brief shots of static with music, never enough to ID the song or station. The FAA and FCC had to work some magic to track down the offending transmitter.
 
I do from experience know that some of those personal locators like the Delorme In Reach, SPOT, etc. can cause interference/jamming with GPS receivers nearby, specifically your higher end mapping-quality GPS receivers. Isn't ADSB also tied in with Iridium satellites like those locators?

Or did you guys happen to have a locator in your pocket?
 
Todd82 said:
I do from experience know that some of those personal locators like the Delorme In Reach, SPOT, etc. can cause interference/jamming with GPS receivers nearby, specifically your higher end mapping-quality GPS receivers. Isn't ADSB also tied in with Iridium satellites like those locators?

Or did you guys happen to have a locator in your pocket?
Click to expand...
I usually fly with my SPOT locator on and tracking in the cockpit and never seems to affect the 530W/430, nor the Stratux talking to WingX.
 
GPS and ADS-B are hundreds of Mhz apart and FCC certified cockpit devices should not be interfering with anything. The ADS-B antenna could also have other antennas doing other things. It could have been a solar flare, I think you can look at solar history and see if there was anything going on that date and time.

I have a GPS with u-blox firmware, there's PC based software for it. It's really cool because if you lost signal you can dig through logs and find out exactly why. Without having those logs you may never know.
 
Just asking. Did you check RAIM? Also about a month or so ago, there was a NOTAM re: GPS outage. It was also in the local paper. (Pensacola area) Paper said that it was centered off the coast, S of Eglin AFB. Eglin is the home of the Armament Test Center. I assume that they test JDAMs there. I know that they tested the MOAB there. Not much of a leap to wonder if an unfriendly nation could cobble up a cheap GPS scrambler to counter the JDAM. Not much of a leap to wonder if the USAF would explore counter measures.
I just skimmed the NOTAM. Forgot most of it. It seemed to cover multiple locations for the outage.
Bob
 
Solar Flares...sure, but maybe like .001% chance given two different days and both losses near GBTs.

Obviously there are far apart on the frequency spectrum but it doesn't mean with absolute certainty there can't be interference.

Only thing in common so far is close proximity to GBTS and using Garmin portable ADSB in devices.

For the flight last month I didn't see any GPS NOTAMS. For the flight on Friday there were GPS notams...and I asked the briefer to give me all the locations in terms a human can understand. Basically in NV and NM. All flights were around 7500msl and in these parts that's 6500agl. No way those outages should reach that far (1400 miles) at our low altitude.

I was wondering if it has to do with the WAAS portion of GPS augmentation (or whatever you call it).
 
I missed the part about the second trip. How close are you flying to the ADS-B tower?
 
Sinistar said:
Okay, during a flight with @WannFly about a month ago we both lost GPS at the same time and our planes were maybe 3-4 miles apart.

On my recent trip out to KRAP and back I also lost GPS.

Both cases had one thing in common: Being fairly close to ADSB Ground Based Transmitters.

Could there be something about them, perhaps the ones for the higher altitudes that are somehow interfering with the GPS satellite signals?

Or maybe its the receiving circuitry on the ADSB In devices.

I have a Garmin GDL39 and @WannFly has a GDL50. So different devices but same vendor, same outage.
Click to expand...

To add to that I lost lost gps on my panel mounted so called bullet proof 480
 
Todd82 said:
I do from experience know that some of those personal locators like the Delorme In Reach, SPOT, etc. can cause interference/jamming with GPS receivers nearby, specifically your higher end mapping-quality GPS receivers. Isn't ADSB also tied in with Iridium satellites like those locators?

Or did you guys happen to have a locator in your pocket?
Click to expand...

I carry a plb on me, but if that was the cause, I would never have GPS. Then it will be a question of getting lost vs survive
 
To answer a few other questions:

I think I was within 20 miles in both cases. Also, I want to think in both cases it was a pair of GBTS near each other too. I don't know the adsb system that well but in case of two near each other, is one broadcasting a cone for higher altitudes and one for lower and maybe it's something about that?

I don't have a spot or inreach. I do have a handheld but is always off. We have a DME but it's pulled. And then a pair of Kx155s to round out anything that can transmit.
 
You are aware of the intentional GPS jamming being conducted in several states, yes?
 
IK04 said:
You are aware of the intentional GPS jamming being conducted in several states, yes?
Click to expand...
See post # 10, the NOTAM'd GPS outages were for 1000+ miles away. In both cases I was at 6500agl, not nearly high enough for those jamming/disruptions to effect something that low.

Also, why only when very near GBTs? (admittedly sample size 2, but 2 different aircraft)
 
Here in Norway, in the last few months have been complaints that the Russians are actually "jamming" the GPS system while doing war games, etc.

The articles on it didn't go into very technical details, so I'm not sure if the GPS was unuseable, or if it was just "off" by a bit.
Norway I think has complained to Russia about this, but not sure what status it is now.
 
Sinistar said:
To answer a few other questions:

I think I was within 20 miles in both cases. Also, I want to think in both cases it was a pair of GBTS near each other too. I don't know the adsb system that well but in case of two near each other, is one broadcasting a cone for higher altitudes and one for lower and maybe it's something about that?

I don't have a spot or inreach. I do have a handheld but is always off. We have a DME but it's pulled. And then a pair of Kx155s to round out anything that can transmit.
Click to expand...
Did you report it to the FAA? Especially if it's consistent, they'll want to investigate.
 
were you over or near an interstate highway? I have seen cases of temporary jamming that the best we could tell was from a semi truck driving underneath, jamming his gps tracking device.
 
tonycondon said:
were you over or near an interstate highway? I have seen cases of temporary jamming that the best we could tell was from a semi truck driving underneath, jamming his gps tracking device.
Click to expand...

He mentioned it happened in the same place at different times so one could assume it is a stationary source.

This article is pretty informative. It even mentions an airport plagued by a truck with a jammer driving by. https://www.gpsworld.com/gnss-systeminnovation-know-your-enemy-12475/

Regardless of the source, if you're able to reproduce the results it is probably worth reporting.
 
Sinistar said:
Okay, during a flight with @WannFly about a month ago we both lost GPS at the same time and our planes were maybe 3-4 miles apart.

On my recent trip out to KRAP and back I also lost GPS.

Both cases had one thing in common: Being fairly close to ADSB Ground Based Transmitters.

Could there be something about them, perhaps the ones for the higher altitudes that are somehow interfering with the GPS satellite signals?

Or maybe its the receiving circuitry on the ADSB In devices.

I have a Garmin GDL39 and @WannFly has a GDL50. So different devices but same vendor, same outage.
Click to expand...
 
Its on again. Today's AOPA Aviation Brief led off with a report that "military jamming" will be conducted in the SE US feb 7-10. Expected to cause GPS and ADS/B outage.
 
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