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PA2AGA > HDDIG 11.04.00 09:52l 150 Lines 6130 Bytes #-9514 (0) @ EU
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Subj: HamDigitalDigest 2000/97D
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European system but it will not be deployed before SA has gone away.
There are presently experiments underway that utilize some new features of
the GPS system to allow control of SA in different regions. The intent
appears to be to allow SA to be selectively applied where the DOD needs it
while removing it from the rest of the world. It may be a while though as
it may require the latest version of the satellites.
I will agree the encryption policy is bizarre. Never let cops set policy.
Jim
>.
Gary Coffman <ke4zv@bellsouth.net> wrote in message
news:ipsmesg5in00i682dmh0j0jrn3j7fbk8kr@4ax.com...
> On Wed, 05 Apr 2000 09:21:11 -0500, W6RCecilA <Cecil.A.Moore@IEEE.org>
wrote:
> >Is it true that there is a deliberate designed-in error to
> >keep our enemies from using GPS for precision military tracking
> >purposes?
>
> Yes, its is called Selective Availability. It is a dither added to the
> information transmitted by the GPS constellation. There is a way
> to cancel this deliberate error if your receiver can receive the second
> channel transmitted by the satellites, and has the decryption key to
> make use of the information. Ironically, however, the times our forces
> have actually been in conflicts, SA has been disabled. That's because
> our military doesn't have sufficient military GPS equipment which can
> nullify the SA limitations, and has been forced to use civilian GPS
> receivers in combat.
>
> A good indication that US forces are about to go adventuring
> has been that your civilian GPS receiver suddenly starts giving
> more accurate position information. That happened just prior
> to the Gulf War for example.
>
> Besides, our enemies can just purchase receivers that use the
> Russian constellation of positioning satellites, which have never
> used a SA dither to reduce their accuracy. It is an absurd situation
> when the only ones locked out of better technology are the ones
> who paid for it (ie the taxpayers).
>
> Meanwhile, while the DOD is dithering our GPS satellites, the
> FAA is busy installing DGPS transmitters to undo the damage
> so that our civilian aircraft can accurately navigate. If that isn't
> an absurd situation, I don't know what is.
>
> There is a similar situation with regard to satellite photo
> reconnaissance. Our government is trying to prevent us
> (John Q Public) from buying from Russian and French
> sources imagery better than it is willing to sell from its
> own satellites. That isn't denying our enemies anything,
> unless the government fears that its enemies are its
> own citizens.
>
> Another similar situation exists with regard to encryption
> technology. The strongest encryption systems can now
> only be obtained from foreign sources. That's because
> our government's absurd policies with regard to encryption
> have forced development to be moved off shore. Again it is
> obvious that the government sees its enemies as being its
> own citizens. Either that, or the government is stupid
> beyond belief. (The latter can't be totally discounted.)
>
> Gary
> Gary Coffman KE4ZV | You make it |mail to ke4zv@bellsouth.net
> 534 Shannon Way | We break it |
> Lawrenceville, GA | Guaranteed |
------------------------------
Date: Wed, 5 Apr 2000 16:13:36 -0700
From: "Jim Donohue" <jim_donohue@computer.org>
Subject: Will a GPS provide continuous, accurate altitude measurements?
It is not so. The GPS errors are worse if anything when moving. You may
not notice as much and some of the programs cheat - they place you on the
road if you are near it - but the actual accuracy is driven by the
deliblerate lies about where the satellites are (SA) combined with the
physical errors inherent in the system.
There is some degradation at the poles do to the placement of the satellite
orbits but other than that the accuracy is much the same everywhere.
Jim
Bill Gunshannon <bill@cs.uofs.edu> wrote in message
news:8cfe7n$13rj$2@info.cs.uofs.edu...
> In article <20000404135227.19705.00000812@ng-fx1.aol.com>,
hrbcrb@aol.com.goaway (KF6HHS) writes:
> |> GPS altitude is not very accurate, it will change at least +/-200 feet
while
> |> sitting in the same location.
>
> The same is true of latitude and longitude. If I use my GPS and laptop
> map software and sit in one place the spot moves all over the place. I
> have seen my house move as far as 2 blocks. GPS seems to be fairly good
> for tracking the location of moving objects, but almost useless for
> staionary ones. I would expect that altitude would be come more accurate
> just as lat/long does when moving and thus providing a greater selection
> of different triangulation data from the satellites.
>
> bill
>
> --
> Bill Gunshannon | de-moc-ra-cy (di mok' ra see) n. Three wolves
> bill@cs.uofs.edu | and a sheep voting on what's for dinner.
> University of Scranton |
> Scranton, Pennsylvania | #include <std.disclaimer.h>
------------------------------
Date: Wed, 5 Apr 2000 20:33:06 -0400
From: "Bob Lewis" <aa4pb@erols.com>
Subject: Will a GPS provide continuous, accurate altitude measurements?
> GPS seems to be fairly good for tracking the location of
> moving objects, but almost useless for staionary ones
The accuracy is the same moving or stationary - you just don't notice
the error so much when you're moving. GPS with a differential receiver
and sitting at a fixed location for a period of time is often used by
surveyors to fix a point within millimeters.
------------------------------
End of Ham-Digital Digest V2000 #97
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