The company I work for makes GPS based clocks.  We care about Selective =
Availability because we are trying to get accuracy down near 10 or 20 =
nS.  Even with it on, it just brings the uncertainty in the time to +- =
200ns RMS or so.  I know I can't pick a P or S time anywhere near that =
accurately!  We watched to see if SA got turned on last week, but it =
didn't.  The current thinking in military circles is to use "regional =
jamming"  They just use standard electronic countermeasure techniques to =
jam the civilian portion of the GPS signal in the area they care about.  =
That way truckers in Ohio still know which parking spot they're in, even =
if there's a war going on in the Middle East.

    Keith

  ----- Original Message -----=20
  From: ChrisAtUpw@..........
  To: psn-l@.................
  Sent: Sunday, September 23, 2001 6:05 PM
  Subject: Re: War-time GPS


       Don't really see why the clocks should be off far enough to =
notice. More likely to be the random jitter on the position fixes which =
died out a couple of years ago. Also airliners are using it now, so it =
is unlikely to be seriously degraded. But do the Afghans use it? Would =
expect it to be operating at max. efficiency all the time. Won't it be =
needed for any air strikes? If it was turned on and off, wouldn't that =
give a warning to the other side? But 100 m at the speed of light is =
about 1/3 micro second --- don't think my seis equipment would know the =
difference.=20

        Regards,=20

        Chris Chapman=20







The company I work for makes GPS based=20
clocks.  We care about Selective Availability because we are trying =
to get=20
accuracy down near 10 or 20 nS.  Even with it on, it just brings =
the=20
uncertainty in the time to +- 200ns RMS or so.  I know I can't pick =
a P or=20
S time anywhere near that accurately!  We watched to see if SA got =
turned=20
on last week, but it didn't.  The current thinking in military =
circles is=20
to use "regional jamming"  They just use standard electronic =
countermeasure=20
techniques to jam the civilian portion of the GPS signal in the area =
they care=20
about.  That way truckers in Ohio still know which parking spot =
they're in,=20
even if there's a war going on in the Middle East.
 
    Keith
 

  
----- Original Message ----- 
  From:=20
  ChrisAtUpw@....... 
  
To: psn-l@.............. 
  
Sent: Sunday, September 23, =
2001 6:05=20
  PM
  
Subject: Re: War-time GPS
  

     Don't really see why the clocks =
should be=20
  off far enough to notice. More likely to be the random jitter on the =
position=20
  fixes which died out a couple of years ago. Also airliners are using =
it now,=20
  so it is unlikely to be seriously degraded. But do the Afghans use it? =
Would=20
  expect it to be operating at max. efficiency all the time. Won't it be =
needed=20
  for any air strikes? If it was turned on and off, wouldn't that give a =
warning=20
  to the other side? But 100 m at the speed of light is about 1/3 micro =
second=20
  --- don't think my seis equipment would know the difference.=20
  

      Regards,=20
  

      Chris Chapman=20