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Why does everyone switch their gps off?

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Why does everyone switch their gps off?
Post by Finn   » Fri Sep 18, 2015 11:20 am

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A GPS receiver is an entirely passive device, it receives signals transmitted by satellite but it doesn't transmit anything.

There are several instances of characters leaving radio receivers running but switching off gps. Does DW believe the myth that GPS devices transmit to satellites?
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Re: Why does everyone switch their gps off?
Post by Weird Harold   » Fri Sep 18, 2015 5:25 pm

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Finn wrote:...Does DW believe the myth that GPS devices transmit to satellites?


Irrelevant. The author doesn't necessarily believe the same thing as his characters, and the characters apparently do believe they can be tracked via their GPS units.

Of course, since we're talking about a fictional world, perhaps GPS units in DWs fictional world do interact with the satellites and/or are trackable. :o
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Re: Why does everyone switch their gps off?
Post by Garth 2   » Sat Sep 19, 2015 11:45 am

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or, since the Puppies start destroying the satellites its simply a battery saving exercise :?:
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Re: Why does everyone switch their gps off?
Post by Loren Pechtel   » Sun Sep 20, 2015 3:47 pm

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Garth 2 wrote:or, since the Puppies start destroying the satellites its simply a battery saving exercise :?:


Yeah, GPS is a battery-eater. I have a camera with GPS but it's only turned on when I want to use it to tag some pictures.
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Re: Why does everyone switch their gps off?
Post by Jonathan_S   » Mon Sep 21, 2015 12:44 pm

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Finn wrote:A GPS receiver is an entirely passive device, it receives signals transmitted by satellite but it doesn't transmit anything.

There are several instances of characters leaving radio receivers running but switching off gps. Does DW believe the myth that GPS devices transmit to satellites?

Well if the GPS receiver uses a heterodyne circuit it might unintentionally radiate on the heterodyne frequency. IIRC that's the same reason that the FAA wants you to shut off radio receivers (walkman, etc) on a flight.

Of course that's true of the other radio receivers as well; so I'm not sure why GPS would get priority to be shut off.
Maybe it was a risk reduction exercise; you might need to receive an emergency radio message so it was worth the minor risk to leave the receivers on, but you wouldn't receive an emergency signal over GPS so reduce your risk slightly by turning it off.
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Re: Why does everyone switch their gps off?
Post by Lord Skimper   » Mon Sep 28, 2015 1:39 am

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there was a text based thing that used gps to send emergency texts. http://www.findmespot.com/en/?cid=102
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Re: Why does everyone switch their gps off?
Post by Weird Harold   » Mon Sep 28, 2015 2:01 am

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Lord Skimper wrote:there was a text based thing that used gps to send emergency texts. http://www.findmespot.com/en/?cid=102


Nope.

Spot uses "satellites" to send text or emergency messages with GPS coordinates attached, but It does NOT send those messages through GPS Satellites.

Your link above wrote:Self Test: SPOT performs a self-test when you initially turn on your SPOT. If all visible lights flash red, the SPOT self-test has found a failure, and SPOT will not send a message. If the On/Off light, GPS light and Message Sending light all blink red, SPOT has a GPS failure, but SPOT may still be able to transmit an SOS or HELP message without your GPS location.
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Re: Why does everyone switch their gps off?
Post by Tenshinai   » Mon Sep 28, 2015 10:55 am

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Most GPS are not shielded from causing "echoes", and with GPS satellites constantly transmitting, there is a risk of causing a steady stream of such echoes.

Anyone who has no clue what i mean, look up how during WWII, the wallies used special gear to track German submarines by exploiting how their radar warning devices were VERY poorly shielded against causing echoes.

To the point where subs could be detected far beyond radar range, just by having some extra detectors listening for the echoes.
While forcing the subs to dive all the time because even weak radar pings could reveal them.
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Re: Why does everyone switch their gps off?
Post by Finn   » Tue Oct 06, 2015 2:54 am

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Tenshinai wrote:Most GPS are not shielded from causing "echoes", and with GPS satellites constantly transmitting, there is a risk of causing a steady stream of such echoes.


Wouldnt military grade GPS be shielded though? And isnt that also true of the 2way radios everyone was quite happy to leave running, especially if the puppies start transmitting to cause the echo?

The military personnel I would have expected to understand how GPS worked and the intricacies involved, so I dont really buy everyone believing the "GPS transmit to satellites" myth.

I just thought it really weird that everyone switched their GPS off without even an consideration of why they were doing it, but were quite happy to leave plenty of other radio receivers running. But then in some ways the capabilities of current day tech seemed really underutilised in the whole book, although I am in the "we could have stood up on our own merits without needing vampires" school.
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Re: Why does everyone switch their gps off?
Post by Tenshinai   » Tue Oct 06, 2015 2:06 pm

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Wouldnt military grade GPS be shielded though?


That reduces the quality and strength of the signal, not much but it isn´t desirable when the signals are already weak.

And isnt that also true of the 2way radios everyone was quite happy to leave running, especially if the puppies start transmitting to cause the echo?


They don´t use the same kind of antenna, because they use much higher transmit power, so it´s rarely an issue there.

I just thought it really weird that everyone switched their GPS off without even an consideration of why they were doing it, but were quite happy to leave plenty of other radio receivers running.


That does sound a bit weird yes. It can be explained as i did above, but to completely avoid the echo risk, you need the gps unit antenna covered up, while regular comradio doesn´t have that risk, any active transmission from it will be vastly more powerful and easier to intercept.

So, under specific conditions, it would be understandable, but only just.
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