# GPS and navigation



## Willbridge (Apr 21, 2022)

Off thread a bit but relates to the issue of navigation. In this case

Land Navigation returns to Army education

It was one of the few parts of Basic Training that I was good at. It turns out that GPS isn't always available.


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## WWW (Apr 21, 2022)

Willbridge said:


> Off thread a bit but relates to the issue of navigation. In this case
> 
> Land Navigation returns to Army education
> 
> It was one of the few parts of Basic Training that I was good at. It turns out that GPS isn't always available.


Ah Ha the compass in your nose navigation - maps aways fascinated me - - - - - 
None of this Winnie the Pooh stuff walking in circles to find someone else walking the same circle and someone else joining each time around !
AND more importantly reading grid coordinates to drop ordinance on the target and not your own position ! LOL


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## Barb Stout (Apr 22, 2022)

Willbridge said:


> Off thread a bit but relates to the issue of navigation. In this case
> 
> Land Navigation returns to Army education
> 
> It was one of the few parts of Basic Training that I was good at. It turns out that GPS isn't always available.


Hmm, I wonder to what extent a GPS "device" can be jammed (as in the Russians jamming GPS signals in Ukraine). And where is the jam, at the satellite level or the receiver level? Would it affect non-targets since satellites orbit? So many technical questions. I know, I know, off-topic, but it does relate to the previous thread in my daily digest about determining where you are while riding a train.


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## UserNameRequired (Apr 22, 2022)

Barb Stout said:


> Hmm, I wonder to what extent a GPS "device" can be jammed (as in the Russians jamming GPS signals in Ukraine). And where is the jam, at the satellite level or the receiver level? Would it affect non-targets since satellites orbit? So many technical questions. I know, I know, off-topic, but it does relate to the previous thread in my daily digest about determining where you are while riding a train.


You can search what the FAA tells us about GPS outages, locations and radius, here is one place






Federal Aviation Administration: NOTAM Search







notams.aim.faa.gov





So, you can put in Location, Predefined Query, GPS NOTAMS, Search.

This is for instance how to decode these: 

!GPS 04/055 ZDV NAV GPS (NATLID GPS 22-01) (INCLUDING WAAS, GBAS, AND ADS-B) MAY NOT BE AVBL WI A 306NM RADIUS CENTERED AT 433430N1125830W (IDA260040) FL400-UNL, 257NM RADIUS AT FL250, 187NM RADIUS AT 10000FT, 189NM RADIUS AT 4000FT AGL, 160NM RADIUS AT 50FT AGL. DLY 1000-1500 2204221000-2204281500

The 433430N1125830W are coordinates and this particular one is west of Idaho Falls.
For ground level, 160NM RADIUS AT 50FT AGL gives us the radius of the outage, and AGL = Above Ground Level.
DLY=Daily
1000-1500 I beleive is the time range, in Zulu time!
2204221000-2204281500 is the dates, year 22, month 04, days 22-28.

And, "stop buzzer" is what you request from ATC if it is causing too much danger for you!

Large assumption=the different radius at different altitudes I think would give clues as to where the jamming originates for these? The way it cones up would lead me to guess this one is jammed from the surface up?


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## Willbridge (Apr 23, 2022)

Barb Stout said:


> Hmm, I wonder to what extent a GPS "device" can be jammed (as in the Russians jamming GPS signals in Ukraine). And where is the jam, at the satellite level or the receiver level? Would it affect non-targets since satellites orbit? So many technical questions. I know, I know, off-topic, but it does relate to the previous thread in my daily digest about determining where you are while riding a train.


It's been a long time since I was keeping up with radio technology. The clodhopper way would be to transmit a powerful signal on the same frequency in the area to be affected. The problem that results is that it affects all users, including perhaps the party doing the jamming.

If you own a satellite you could transmit a fake signal overpowering the official signal and then depending on the sophistication of the receiving equipment it might or might not be able to detect the fake.

GPS signals have all the usual problems with radio signals, such as being blocked by terrain, tall buildings, drifting signals of other transmitters, etc.


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## cirdan (Apr 23, 2022)

Alternatively , you could create an alternative and independent navigation and location system that your opponent does not know about or cannot use and then block GPS . This doesn’t need to be global or sophisticated. It just needs to be good enough for purpose within the local area


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## WWW (Apr 23, 2022)

Amazing all this navigation stuff GPS Satellites (and not the porta-p type) and YET trains can't navigate off the TRACKS at least not YET !

With trains you are bound to take where the tracks are laid out - with flight you can go like a sober or drunken crow from point to point.
YET (there I go and use that word again) when flight arrives at its destination you gotta land someplace - landing on railroad tracks is
not the best move and water without floats is not recommended either - OH and stay off the roads - look out for traffic - maybe best
to find a corn field to set down in - and what's this about an airport something like a depot in that corn field ! The best part about tracks
is that more in likely they will be in the center of town or business center - now about those corn field airports (depots) you need some
sort of transportation to that town center.

Amazing how far we have come in transportation - - - - - - - - - - science and technology !


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## west point (Apr 23, 2022)

Remember jamming of GPS affects PTC except for basic ACSES. Not well known but many of the airports with precision CAT =3C have local ground GPS transmitters that transmit local signals down to mm accuracy.
Partial description of what an approach is like. Localizer capture outside of outer marker point. all 3 auto pilots engaged. Glide slope capture at outer marker or before. radio altimeter call outs. 50, 30, 30, 10,5, . Then plane touches down on main gear, throttle retarded, nose lowers, nose touches down and you may see or may not see high intensity runway centerline lights. Reverse thrust and brake.

Then try to find runway turnoff lights and taxi lights. My most difficult experience took 20 - 25 minutes to find gate. Every airport different.

Note some airlines might operate these approaches slightly different.


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## jis (Apr 23, 2022)

west point said:


> Remember jamming of GPS affects PTC except for basic ACSES.


What aspect of any ACSES requires GPS? IOW what is the specific importance of the word "basic"?


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