National Space Policy: NSDD-42 (issued on July 4th, 1982)

In article ,
Ian Stirling wrote:
The power over an entire hemisphere of the earth is some 50W.
It's trivial to swamp a reciever with some millions of times the nominal
signal.

One caveat: it's not quite as easy as one might think, because the GPS
signals are *already* below the noise floor with typical antennas, and the
digital correlation method used to hear them anyway is quite robust. Just
raising the noise level somewhat won't do much. You have to either raise
it a whole lot, or get clever.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

(Henry Spencer) wrote:

Ian Stirling wrote:

GPS is almost trivial to jam.
I could build a jammer to kill military/civilian GPS within 10Km for
under $10 or so.
$100 and a balloon maybe 150Km.

The power over an entire hemisphere of the earth is some 50W.
It's trivial to swamp a reciever with some millions of times the nominal
signal.

One caveat: it's not quite as easy as one might think, because the GPS
signals are *already* below the noise floor with typical antennas, and the
digital correlation method used to hear them anyway is quite robust. Just
raising the noise level somewhat won't do much. You have to either raise
it a whole lot, or get clever.

A nation at war (or about to go to war) could easily find the needed
resources to provide such jamming, though.

In sci.space.policy Peter Stickney wrote:
In article ,
"Scott M. Kozel" writes:
(Henry Spencer) wrote:

Ian Stirling wrote:

GPS is almost trivial to jam.
I could build a jammer to kill military/civilian GPS within 10Km for
under $10 or so.
$100 and a balloon maybe 150Km.

The power over an entire hemisphere of the earth is some 50W.
It's trivial to swamp a reciever with some millions of times the nominal
signal.

One caveat: it's not quite as easy as one might think, because the GPS
signals are *already* below the noise floor with typical antennas, and the
digital correlation method used to hear them anyway is quite robust. Just
raising the noise level somewhat won't do much. You have to either raise
it a whole lot, or get clever.

A nation at war (or about to go to war) could easily find the needed
resources to provide such jamming, though.

ANd thus provide a few zillion targetting beacons that will be
elimanated as the first course of business.

It's not at all as easy as you seem to think. Not only are the
signals hard to identify withing the noise, if you aren't a GPS
receiver, but, as far as the receiver is concerned, the signal's
highly directional. If it's not coming from above, and it doesn't
exhibit the propper doppler shifts, it's not a real signal, and can be
safely ignored.

Preceicely how does the receiver differentialte between signal coming
from the above vs. not? To differenctiate the source you need at least two
directional antennas. Not just that but air-balloons are cheap, increase
coverage abd would also be seen as being above by receivers.



--
Sander

+++ Out of cheese error +++

In sci.space.policy Henry Spencer wrote:
In article ,
Ian Stirling wrote:
The power over an entire hemisphere of the earth is some 50W.
It's trivial to swamp a reciever with some millions of times the nominal
signal.

One caveat: it's not quite as easy as one might think, because the GPS
signals are *already* below the noise floor with typical antennas, and the
digital correlation method used to hear them anyway is quite robust. Just
raising the noise level somewhat won't do much. You have to either raise
it a whole lot, or get clever.

I know.
I'm talking of raising the power recieved into a broadband reciever well
above the thousand or ten thousand times gain that the digital correlation
gives.
A 5W transmitter can hit a million times the power of a 50W global
transmitter at around a 4Km radius.
It will be very, very hard to generate a usable position even given
sharply directional antennas pointed at each satellite.

"Sander Vesik" wrote in message
...
Preceicely how does the receiver differentialte between signal coming
from the above vs. not? To differenctiate the source you need at least two
directional antennas. Not just that but air-balloons are cheap, increase
coverage abd would also be seen as being above by receivers.
And would be almost immediate targets for HARM missles.

In article ,
"Ami Silberman" wrote:

"Sander Vesik" wrote in message
...
Preceicely how does the receiver differentialte between signal coming
from the above vs. not? To differenctiate the source you need at least two
directional antennas. Not just that but air-balloons are cheap, increase
coverage abd would also be seen as being above by receivers.
And would be almost immediate targets for HARM missles.

I think Sander's point is that such balloons are MUCH cheaper than HARM
missiles, and likely to be more numerous for a well-equipped and
-trained foe.

That being said, since most weapons equipped with GPS have alternate
guidance systems, and as others have pointed out, degrading GPS signals
in the vicinity of the target may make little or no difference.

--
Herb Schaltegger, B.S., J.D.
Reformed Aerospace Engineer
Columbia Loss FAQ:
http://www.io.com/~o_m/columbia_loss_faq_x.html

Sander Vesik wrote in message ...
In sci.space.policy Peter Stickney wrote:
In article ,
"Scott M. Kozel" writes:
(Henry Spencer) wrote:

Ian Stirling wrote:

GPS is almost trivial to jam.
I could build a jammer to kill military/civilian GPS within 10Km for
under $10 or so.
$100 and a balloon maybe 150Km.

The power over an entire hemisphere of the earth is some 50W.
It's trivial to swamp a reciever with some millions of times the nominal
signal.

One caveat: it's not quite as easy as one might think, because the GPS
signals are *already* below the noise floor with typical antennas, and the
digital correlation method used to hear them anyway is quite robust. Just
raising the noise level somewhat won't do much. You have to either raise
it a whole lot, or get clever.

A nation at war (or about to go to war) could easily find the needed
resources to provide such jamming, though.

ANd thus provide a few zillion targetting beacons that will be
elimanated as the first course of business.

It's not at all as easy as you seem to think. Not only are the
signals hard to identify withing the noise, if you aren't a GPS
receiver, but, as far as the receiver is concerned, the signal's
highly directional. If it's not coming from above, and it doesn't
exhibit the propper doppler shifts, it's not a real signal, and can be
safely ignored.

Preceicely how does the receiver differentialte between signal coming
from the above vs. not? To differenctiate the source you need at least two
directional antennas. Not just that but air-balloons are cheap, increase
coverage abd would also be seen as being above by receivers.

The receiver uses data from multiple sats and an internal table to determine
where it is. I don't think it can tell where the sat is in space so much
as it uses look-up tables on the assumption that the sat is where it is
supposed to be. However, I doubt you could fool a reciever into thinking your
baloons are sats since they would be too close to each other... unless
you also could modify the look-up table in the receiver remotely but that'd
probably only work well in a situation where the receiver can't see any
of the real sats.. like say inside of a cave.

My guess.

-McDaniel

I once heard a USAF general describe GPS data as being like air....both
sides on the battlefield have the use of it.

Perhaps he said this to obfuscate the secret balloon plan.

In sci.space.policy Herb Schaltegger wrote:
In article ,
"Ami Silberman" wrote:

"Sander Vesik" wrote in message
...
Preceicely how does the receiver differentialte between signal coming
from the above vs. not? To differenctiate the source you need at least two
directional antennas. Not just that but air-balloons are cheap, increase
coverage abd would also be seen as being above by receivers.
And would be almost immediate targets for HARM missles.

I think Sander's point is that such balloons are MUCH cheaper than HARM
missiles, and likely to be more numerous for a well-equipped and
-trained foe.

Yes, and easily replaceable. And also redirects the use of HARM missiles
from say targeting radars. Nobody has an infinite supply of HARM missiles
and they take real time money and effort to transport.


That being said, since most weapons equipped with GPS have alternate
guidance systems, and as others have pointed out, degrading GPS signals
in the vicinity of the target may make little or no difference.


Yes - but with reduced capability, you will have a larger number of
misses (and say Tomahawk, a rather expensive toy has a pretty good track
record of missing even with GPS available) which translates into
increased costs and increased logistics hurdles and more missions by
planes. It also affects ground operations.

--
Sander

+++ Out of cheese error +++

In article ,
Ian Stirling wrote:
I'm talking of raising the power recieved into a broadband reciever well
above the thousand or ten thousand times gain that the digital correlation
gives.

Bear in mind that some of the smarter military GPS receivers can alter
their antenna pattern to point a deep null at a jammer (maybe even more
than one). Noise jammers are really easy for a smart receiver to spot.

Now, meaconing is another story. (Meaconing is lousing up time-based
radio navigation systems by receiving the legitimate signal, running it
through a time delay, and rebroadcasting it at somewhat higher power.)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |