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#263232 - 09/04/13 11:25 AM Re: 911 Calls [Re: chaosmagnet]
WB2QGZ Offline
Newbie

Registered: 03/01/03
Posts: 25
Loc: FN30gq Long Island, NY
Originally Posted By: chaosmagnet
Originally Posted By: WB2QGZ
Cellular E911 uses handset GPS on most CDMA networks (which can not be disabled by the user)


Are you sure that's right? I believe that whether GPS can be disabled is determined by the handset, not the network. Some handsets do not permit disabling GPS, while others do.

73 de chaosmagnet


I have never seen a CDMA handset not provide GPS info to the PSAP as long as it was not in a bad position for a fix, including iPhones on the metroPCS and Sprint networks. I have no experience testing on Verizon. I was always advised from the beginning of the phase 1 hi res location rollout that the 911 location function was not able to be defeated in the handset through normal means. Considering the gyrations the carriers have to go through to insure proper configuration and continual verification of the 911 location system it wouldn't make sense, IMO, to allow handsets on the network that allow you to disable location on the system. It's kind of a big deal to carriers when a PSAP can't obtain location info from the handset in a 911 call, and if they get a few of them the places near me are usually initiating troubleshooting with the carrier and location service vendor.

There may be some handsets somewhere I have not seen that let you turn it off.

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#263233 - 09/04/13 11:28 AM Re: 911 Calls [Re: hikermor]
Quietly_Learning Offline
Member

Registered: 05/29/12
Posts: 164
E911cannot be turned off. It is required by the fcc:

http://www.fcc.gov/guides/wireless-911-services:

I searched to see if there was a hack to turn it off, very unwise if you have an emergency and can't get help, and you can't short of using a tin foil hat.

I use a find my phone app that if you text a code word will return your gps coordinates and the street address for the police. I use it to send my last known address when I'm playing in the woods. If you have a signal to make a call you can text yourself first or during the call to get more detailed info of where you are. It is also important to download the google map of where you are traveling so the street address can be found if you lose data.

This is my 100th post!!! After over 10 years of reading the forum I'm now officially a "member" :-)
Mods where should I send my address for my free toaster?

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#263237 - 09/04/13 12:23 PM Re: 911 Calls [Re: Quietly_Learning]
chaosmagnet Offline
Sheriff
Carpal Tunnel

Registered: 12/03/09
Posts: 3842
Loc: USA
Originally Posted By: Quietly_Learning
E911cannot be turned off. It is required by the fcc:

http://www.fcc.gov/guides/wireless-911-services


I don't think that the FCC regulations state that -- it appears to me that the provider must have the capability.

The only modern phone I know much about is the AT&T iPhone, and I'm pretty confident that when Location Services is turned completely off that the GPS chip is turned completely off. If I'm right about that, iPhone users who do that would be left with the network's location-finding ability rather than the handset's onboard reporting of location.

Originally Posted By: wikipedia
The U.S. Federal Communications Commission (FCC) has several requirements applicable to wireless or mobile telephones:
Basic 911: All 911 calls must be relayed to a call center, regardless of whether the mobile phone user is a customer of the network being used.
E911 Phase 1: Wireless network operators must identify the phone number and cell phone tower used by callers, within six minutes of a request by a PSAP.
E911 Phase 2:
95% of a network operator's in-service phones must be E911 compliant ("location capable") by December 31, 2005. (Several carriers missed this deadline, and were fined by the FCC.)
Wireless network operators must provide the latitude and longitude of callers within 300 meters, within six minutes of a request by a PSAP. Accuracy rates must meet FCC standards on average within any given participating PSAP service area by September 11, 2012 (deferred from September 11, 2008).
Location information is not only transmitted to the call center for the purpose of sending emergency services to the scene of the incident, it is used by the wireless network operator to determine to which PSAP to route the call.


Let me be clear that I do not advocate turning this feature off when calling 911!

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#263238 - 09/04/13 12:40 PM Re: 911 Calls [Re: hikermor]
JPickett Offline
Enthusiast

Registered: 08/03/12
Posts: 264
Loc: Missouri
"Mods where should I send my address for my free toaster?"
Just stand outside in shorts on a sunny day. As soon as enough satellites are clustered overhead, the toasting will commence. =^P

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#263240 - 09/04/13 01:51 PM Re: 911 Calls [Re: Pete]
Glock-A-Roo Offline
Old Hand

Registered: 04/16/03
Posts: 1076
Originally Posted By: Pete
My GPS puts out degrees, minutes, decimal minutes.
I've got no problem passing that on to a dispatcher. but what words exactly do I say to them ...

"here are my coordinates.
I'm giving you degrees, minutes, and decimal minutes.
do you understand over?"

WILL this conversation make sense to them?
Or do I describe the system some other way??


I explored this kind of thing with some local agencies. My chief concern was which horizontal datum they used.

Funny conversation I had with a medical transport helicopter pilot:

G-A-R: "What datum does your onboard GPS nav system use?"

pilot: "Degrees, minutes, fractions of minutes."

G-A-R: "OK, thanks..." <shakes head>

While land-based people often switch their GPS unit's horizontal datum between NAD27 (or other local datum) and WGS84 to jive with the paper maps they have, aviation and naval assets almost always stick with WGS84. Of course I am quite open to correction on this, I know we have some solid SMEs on the forum.

Regardless, I would always include the horizontal datum when reporting coordinates. If the people on the other end of the line have the knowhow to use that info, great; if they don't then it won't hurt them to hear the info.

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#263242 - 09/04/13 02:15 PM Re: 911 Calls [Re: Quietly_Learning]
chaosmagnet Offline
Sheriff
Carpal Tunnel

Registered: 12/03/09
Posts: 3842
Loc: USA
Originally Posted By: Quietly_Learning

Mods where should I send my address for my free toaster?


Unfortunately with the ETS forum budget cuts we can only send out a cookie. The good news is that we've already delivered it to you. If you are using Firefox on Windows, look in the %APPDATA%\Mozilla\Firefox\Profiles\ directory, open your Firefox profile, and look inside the cookies.sqlite file. If you're using some other OS/browser combo, let me know which one and I'll help you find your cookie.

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#263247 - 09/04/13 02:28 PM Re: 911 Calls [Re: hikermor]
gonewiththewind Offline
Veteran

Registered: 10/14/08
Posts: 1517
Those cookies don't taste very good.

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#263248 - 09/04/13 03:06 PM Re: 911 Calls [Re: chaosmagnet]
WB2QGZ Offline
Newbie

Registered: 03/01/03
Posts: 25
Loc: FN30gq Long Island, NY
Not 100% sure about at&t, but the GSM network I currently service uses TDOA, or automated differential time of arrival at 4 or 5 sites to determine location. Accuracy to 3 m or better, similar to GPS. Not sure if there's a technical reason that you can't use GPS over the GSM like you can on CDMA though. Considering that at&t handsets can be configured for the network I'm at I'd guess they might also use TDOA in which case GPS doesn't matter.

Anyone else know for sure how at&t does 911 location?

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#263249 - 09/04/13 03:20 PM Re: 911 Calls [Re: Pete]
AKSAR Offline
Veteran

Registered: 08/31/11
Posts: 1233
Loc: Alaska
Originally Posted By: Pete
My GPS puts out degrees, minutes, decimal minutes.
I've got no problem passing that on to a dispatcher. but what words exactly do I say to them ...
I would do it like the following example:

"My location is six one degrees, one one point six nine three minutes North, and one four nine degrees, five four point three five six minutes West, WGS84. Please read that back to me to confirm."

Speak slowly and clearly, and say each digit separately (say "six one", not "sixty one").

(That location (61° 11.693'N and 149° 54.356'W) is in the parking lot in front of the Anchorage REI store. smile )
_________________________
"Toto, I've a feeling we're not in Kansas any more."
-Dorothy, in The Wizard of Oz

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#263250 - 09/04/13 03:26 PM Re: 911 Calls [Re: Glock-A-Roo]
AKSAR Offline
Veteran

Registered: 08/31/11
Posts: 1233
Loc: Alaska
Originally Posted By: Glock-A-Roo

While land-based people often switch their GPS unit's horizontal datum between NAD27 (or other local datum) and WGS84 to jive with the paper maps they have, aviation and naval assets almost always stick with WGS84.
Modern nautical charts are now in WGS84, and scaled in degrees, minutes, and tenths of minutes. I believe aviation charts are likewise.

Note that one minute of latitude equals one nautical mile.
_________________________
"Toto, I've a feeling we're not in Kansas any more."
-Dorothy, in The Wizard of Oz

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