[aprssig] Terrestrial Threat to GPS Has Now Hit The Mainstream Media

[Brian Webster]

Bernard,

                Light Squared is planning on deploying a cellular type
network of high powered transmitters in spectrum that was previously
designated for satellite services which is why it is right next to the GPS
band. They will be high power directional antennas designed to deliver high
speed internet services. Make no doubt that they will run high power and do
so over channels that will be from 5 to 20 MHz wide. Signals like this have
a high potential to swamp the GP receiver that are sensitive down to -158
dBm! I work in this wireless ISP industry. They will deploy the cheapest
radios they can to keep the cost of deployment down. My fear is that this
cheap radios will not have enough filtering in them to keep from splattering
signal in to the GPS band. While this level of signal won't be an issue for
a radio that can only hear down to -90 dBm or so, those GPS receivers at
-158 will have a hard time rejecting those signal especially when it becomes
a cumulative problem with hundreds of these towers deployed all over. These
wireless internet networks are design to offer residential broadband
service. They will be almost continuous duty cycles from the tower side.

 

Thank You,

Brian N2KGC

www.wirelessmapping.com

www.Broadband-Mapping.com

 

From: aprssig-bounces at tapr.org [mailto:aprssig-bounces at tapr.org] On Behalf
Of Bernard Van Haecke
Sent: Sunday, April 10, 2011 1:53 PM
To: TAPR APRS Mailing List
Subject: Re: [aprssig] Terrestrial Threat to GPS Has Now Hit The Manstream
Media

 

This is a non issue unless the jammer is sitting on a sat or airplane.

If terrestrial and uses high power, he will be DF'ed in no time.

Otherwise, this story is a joke.

Bernard

Sent from my EVO android phone

On Apr 10, 2011 10:44 AM, "Alex Carver" <kf4lvz at yahoo.com> wrote:
> 
>> From: "Rahn Abbott" 
>> 
>> Ummmm, you do know that that US Military GPS units and your
>> Garmin Etrex are
>> not listening to the same radio signals right? You do know
>> military and US
>> government GPS runs on a completely different system? 
> 
> 
> No, the military listens to both L1 at 1.57542 GHz (the "civilian" GPS
signal) and L2 at 1.22760 GHz, the military-only GPS signal. They use both
signals in order to determine delays caused by the ionosphere which improves
the accuracy of the military GPS receivers. If interference is caused to the
L1 signal it will affect both civilian and military users.
> 
> A military GPS receiver and a civilian GPS receiver both listen to L1 but
they each use a different chipping code (civilian uses unencrypted C/A and
military uses both unencrypted C/A and encrypted P). Only the military GPS
receiver listens to L2 at the same time.
> 
> Later on there will be new codes (L1C and M) as new satellites are put in
orbit but they will still have both civilian and military codes sitting on
L1. In addition, civilians will soon have access to L2 in the form of a
civilian code on L2 (L2C) which will allow for some basic ionospheric
corrections to improve accuracy and reduce drift. It won't be as accurate as
the military receivers but better than the current L1-only receivers.
> 
> _______________________________________________
> aprssig mailing list
> aprssig at tapr.org
> https://www.tapr.org/cgi-bin/mailman/listinfo/aprssig

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.tapr.org/pipermail/aprssig_lists.tapr.org/attachments/20110412/6a2380da/attachment.html>