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10-20-2020, 10:20 AM   #1
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Lack of GPS

Something peculiar happened to me about two weeks ago. I was in the mountains and a cousin came to visit. We went on a road trip which took us up to a 9000 foot mountain top which had a beautiful scenic view. I had my K-1 and snapped away. I wanted to know what the exact elevation was (no markers) and assumed my K-1 would record the elevation. After I got home, I pulled up the data on that shoot, and to my surprise, there was no GPS data for the mountain top. Each and every one of my shots there lacked GPS data though shots before I got there and shots afterwards had it intact.

At first, I thought it was my fault for not giving the K-1 enough time to lock but some of those shots were almost a minute after I had the camera turned on. Then came the realization that there was a forest service repeater on the mountain top close to where I had taken all those shots. I think now that it was responsible for the lack of GPS info and in some way was creating interference that disabled the GPS reception in that area. There were no microwave dishes, however, but something on the site had prevented my K-1 from getting the data.

I finally had to resort to using Google Earth which gave me the elevation for the location

Anyone familiar with forest service repeater sites that can fill me in??

10-20-2020, 10:34 AM   #2
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I wonder if you were below the repeater and had no signal?


Hang up and DRIVE!
10-20-2020, 12:17 PM   #3
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Sometime my phone loses GPS signals during driving. In mountains area that happens more often than on the flat. That and clouds on the sky is more probable cause in your case.
10-20-2020, 01:30 PM - 1 Like   #4
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QuoteOriginally posted by Bob 256 Quote
I think now that it was responsible for the lack of GPS info and in some way was creating interference that disabled the GPS reception in that area.
Seems like a long shot. The primary GPS bands are somewhat protected from other transmissions. How close were you to the repeater tower? 1/r-squared is your friend. Unless you were within a few 10s of meters, I wouldn't expect any such transmitter to overload the K-1 receiver (unless it's got really crappy filtering!). Are you sure you didn't bump the GPS on/off switch? Does the status of the GPS receiver show in EXIF?

I would guess that any repeaters like that are running at frequencies of a few hundred MHz at most, whereas the primary GPS frequency is at almost 1.6 GHz.

QuoteOriginally posted by jumbleview Quote
clouds on the sky is more probable cause
NO! Even the densest clouds will not significantly absorb at GPS frequencies (take it from a radio astronomer who has observed on very cloudy days!)

Being in a mountain valley with reduced sky coverage could make a difference - you need to have a good view of at least 3 and preferably 4 GPS satellites for a good position and time solution. Time and position (x,y,z) are 4 coordinates - you need data from 4 satellites to solve for all 4! Some receivers will try for a 3 parameter solution by assuming either that the receiver knows what time it is, or that you are at sea level.

10-20-2020, 01:54 PM   #5
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QuoteOriginally posted by Bob 256 Quote
At first, I thought it was my fault for not giving the K-1 enough time to lock but some of those shots were almost a minute after I had the camera turned on.
Based on my experience with K-1, a minute is quite a short time for getting a fix. Please keep in mind that K-1, as far as I know, does not use A-GPS, and as such needs to obtain data directly from GPS signal. Due to low bitrate of the latter, it takes a while, the more the longer you have not been using GPS.

Last edited by pentageek; 10-20-2020 at 02:05 PM. Reason: typo
10-20-2020, 01:59 PM - 2 Likes   #6
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Phones have spoiled us with agps. We expect instant lock. I still remember my dedicated external car gps from several years back taking 5 minutes or more to lock depending on the location and sky visibility. Ideally the k1 would ask the phone for agps days to jumpstart the location calculation.
10-20-2020, 02:47 PM   #7
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I know when driving through mountains I can lose satellite radio signals when close to the edge of a mountainside, but I would not think that would happen on top of the mountain.
10-20-2020, 04:06 PM   #8
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You need to turn on the GPS engine via the small button on the right side of the viewfinder hump, otherwise you will not get any GPS reception. Do you remember doing that?

10-20-2020, 04:24 PM   #9
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There is a spot in Scotland where the GPS signals simply go away. At least that is what happened in the Vauxhall Integra I was driving. Located at a three way split in the road.

No trees, not all that many peaks, clear skies once (driving down into Oban) cloudy driving from Oban to Loch Loman and back. Raining on the way back. Since I was driving, I did not look at the phone and the K-3II was in the rear. We did not stop, so I can't say if the K-3II could lock on.

The K-3II and my phone would lose - or better - not obtain GPS signals while on most trains in Germany, Czech Republic, Slovenia, Austria and Poland. Trains are very good GPS faraday cages.
10-21-2020, 11:23 AM   #10
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QuoteOriginally posted by AstroDave Quote
Seems like a long shot. The primary GPS bands are somewhat protected from other transmissions. How close were you to the repeater tower? 1/r-squared is your friend. Unless you were within a few 10s of meters, I wouldn't expect any such transmitter to overload the K-1 receiver (unless it's got really crappy filtering!). Are you sure you didn't bump the GPS on/off switch? Does the status of the GPS receiver show in EXIF?

I would guess that any repeaters like that are running at frequencies of a few hundred MHz at most, whereas the primary GPS frequency is at almost 1.6 GHz.



NO! Even the densest clouds will not significantly absorb at GPS frequencies (take it from a radio astronomer who has observed on very cloudy days!)

Being in a mountain valley with reduced sky coverage could make a difference - you need to have a good view of at least 3 and preferably 4 GPS satellites for a good position and time solution. Time and position (x,y,z) are 4 coordinates - you need data from 4 satellites to solve for all 4! Some receivers will try for a 3 parameter solution by assuming either that the receiver knows what time it is, or that you are at sea level.
I was confused too because I didn't think any communication frequencies were in the GPS range. I was about 40 feet away when the first GPS failure occurred and it happened at a range of about 200 feet from the repeater also. No clouds in the sky and when I got back to my cabin, the camera was registering GPS data in the cabin which has a metal roof!!, so I know the GPS receiver was working fine. The GPS was definitely on the whole trip. Here's what I got about a half-mile away from the site (header and data) and at the site (the latter in red - header only). At this point, I'm back to thinking it was lock time, since I had turned the camera off between shots, but it's peculiar to just those shots and not others which I didn't treat any differently. Maybe a government "black site" - I have pictures of it???
Attached Images
 

Last edited by Bob 256; 10-21-2020 at 11:33 AM.
10-21-2020, 11:47 AM - 1 Like   #11
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QuoteOriginally posted by Bob 256 Quote
Something peculiar happened to me about two weeks ago. I was in the mountains and a cousin came to visit. We went on a road trip which took us up to a 9000 foot mountain top which had a beautiful scenic view. I had my K-1 and snapped away. I wanted to know what the exact elevation was (no markers) and assumed my K-1 would record the elevation. After I got home, I pulled up the data on that shoot, and to my surprise, there was no GPS data for the mountain top. Each and every one of my shots there lacked GPS data though shots before I got there and shots afterwards had it intact.

At first, I thought it was my fault for not giving the K-1 enough time to lock but some of those shots were almost a minute after I had the camera turned on. Then came the realization that there was a forest service repeater on the mountain top close to where I had taken all those shots. I think now that it was responsible for the lack of GPS info and in some way was creating interference that disabled the GPS reception in that area. There were no microwave dishes, however, but something on the site had prevented my K-1 from getting the data.

I finally had to resort to using Google Earth which gave me the elevation for the location

Anyone familiar with forest service repeater sites that can fill me in??
Highly unlikely that repeater is working on the frequency range of GPS. That would violate FCC rules and would be found quickly as it would interfere with aviation who would quickly notice.

It's possible there's a gap in the ephemeris file for the satellites (position locations) in that location (on the camera) or maybe a GPS jamming event if you have any military bases within a few hundred miles. The past few years they've been doing significant testing on GPS jamming equipment (Russia is really good at GPS jamming).

When it's the ephemeris file it's usually an outage in a small or sometimes large area for a few minutes to maybe 30 minutes. Or it could have been space weather blocking the GPS signal for a period of time.
https://www.swpc.noaa.gov/

FAA will GPS NOTAM an area if the military is testing. Those can be found linked below.

KZLC is Salt Lakes region. There is GPS outages notams within 400ish miles at the moment, possible in the timeframe you mentioned as well.

https://www.navcen.uscg.gov/pdf/gps/gpsnotices/GPS_Interference.pdf

10/120 (A0359/20) - NAV GPS (WSMRNM GPS 20-11) (INCLUDING WAAS, GBAS,
AND ADS-B) MAY NOT BE AVBL WI A 437NM RADIUS CENTERED AT
332930N1062835W (TCS059042) FL400-UNL,
392NM RADIUS AT FL250,
317NM RADIUS AT 10000FT,
311NM RADIUS AT 4000FT AGL,
294NM RADIUS AT 50FT AGL. 24 OCT 06:00 2020 UNTIL 24 OCT 12:00 2020. CREATED:
21 OCT 01:42 2020

10/103 (A0354/20) - NAV GPS (NTTR GPS 20-13) (INCLUDING WAAS, GBAS, AND
ADS-B) MAY NOT BE AVBL WI A 466NM RADIUS CENTERED AT 371934N1154249W
(BTY041059) FL400-UNL,
417NM RADIUS AT FL250,
340NM RADIUS AT 10000FT,
298NM RADIUS AT 4000FT AGL,
228NM RADIUS AT 50FT AGL. 23 OCT 06:00 2020 UNTIL 23 OCT 08:00 2020. CREATED:
19 OCT 05:34 2020

10/099 (A0353/20) - NAV GPS (WSMRNM GPS 20-11) (INCLUDING WAAS, GBAS,
AND ADS-B) MAY NOT BE AVBL WI A 437NM RADIUS CENTERED AT
332930N1062835W (TCS059042) FL400-UNL,
392NM RADIUS AT FL250,
317NM RADIUS AT 10000FT,
311NM RADIUS AT 4000FT AGL,
294NM RADIUS AT 50FT AGL. 23 OCT 08:00 2020 UNTIL 23 OCT 12:00 2020. CREATED:
19 OCT 02:37 2020

10/088 (A0352/20) - NAV GPS (WSMRNM GPS 20-11) (INCLUDING WAAS, GBAS,
AND ADS-B) MAY NOT BE AVBL WI A 437NM RADIUS CENTERED AT
332930N1062835W (TCS059042) FL400-UNL,
392NM RADIUS AT FL250,
317NM RADIUS AT 10000FT,
311NM RADIUS AT 4000FT AGL,
294NM RADIUS AT 50FT AGL.
DLY 0600-1200. 21 OCT 06:00 2020 UNTIL 22 OCT 12:00 2020. CREATED: 17 OCT 22:56
2020

https://www.notams.faa.gov/dinsQueryWeb/

Defense Internet NOTAM Service

Last edited by LeeRunge; 10-21-2020 at 12:00 PM.
10-21-2020, 12:27 PM   #12
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QuoteOriginally posted by LeeRunge Quote
... space weather blocking the GPS signal for a period of time. ...
That a lot of useful info in your post. May you elaborate a little more about "space weather"? What the physics behind this term?
10-21-2020, 02:15 PM - 2 Likes   #13
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QuoteOriginally posted by jumbleview Quote
That a lot of useful info in your post. May you elaborate a little more about "space weather"? What the physics behind this term?
NOAA can probably explain better than I can.

Basically, solar activity can affect GPS causing outages.

Space Weather and GPS Systems | NOAA / NWS Space Weather Prediction Center


The actual GPS signal isn't very strong from the satellites.

For those who don't know how it works, basically it triangulates your position by finding the length of distance from the satellite (position in ephemeris file) by measuring the time the signal left the satellite to when it arrives at your receiver. This is done with the use of atomic clocks. As the radio signal speed is known the length can be accurately calculated. You need 3 satellites for position and 4 for position and altitude.

Nothing is transmitted from a GPS receiver. It's all downlink from the satellite constellation.


Prior to this another system on land called LORAN (used for maritime navigation) was common and may again be used in the E-LORAN format in the future.

Aircraft used ADF or VOR navigation aids prior to GPS. Basically directional radio signals similar to a spoked wheel each with a radial bearing. ADF was essentially an AM radio transmitter and a receiver that pointed you in the direction of it.

Going even further back the use of Sextants (WW1 and 2 as well) was the state of the art from I think the 1700's onward until radio was invented. It works in a similar way to GPS by triangulating your location based on the known location and travel of the stars.
10-21-2020, 02:32 PM   #14
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The GPS frequencies are entirely free from other legitimate communication signals. The keyword here is legitimate. It is easy for faulty or poorly maintained transmitters to emit unintended frequencies that interfere with GPS. These unintended frequencies would be much weaker than the intended signal but if you are close to the transmitter it is enough to block the GPS signal. The standard GPS signal is actually very easy to block, whether intentionally or otherwise as it is very weak and not spread very widely across the spectrum. Being close to radio transmitting stations, PMR repeaters or anything else that transmits in VHF and UHF will easily block it.

Depending on where you are you could even be experiencing deliberate jamming. In Libya for instance last year jamming was used extensively and its effect was felt far beyond the intended area blocking GPS receivers on high ground even as far away as Malta and Sicily.
10-22-2020, 03:20 AM   #15
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QuoteOriginally posted by Bob 256 Quote
At this point, I'm back to thinking it was lock time, since I had turned the camera off between shots
Assuming that you had a fix shortly before the blackout, issues with long lock time are highly unlikely, as the camera obtained virtually all data already, and its biggest chunk (i.e. ephemeris and almanac) has quite long expiration date. Very mysterious case:/

Last edited by pentageek; 10-22-2020 at 03:22 AM. Reason: clarification
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