Re: Detecting IEDs...


"Randy Poe" <poespam-trap@xxxxxxxxx> wrote in message
news:1193506941.518926.196160@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Oct 27, 10:45 am, "Tom Potter" <tdp1...@xxxxxxxxx> wrote:
"Randy Poe" <poespam-t...@xxxxxxxxx> wrote in message

news:1193418747.110413.215770@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Oct 26, 12:26 pm, "Tom Potter" <tdp1...@xxxxxxxxx> wrote:

"Sam Wormley" <sworml...@xxxxxxxxx> wrote in message

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Tom Potter wrote:
"Sam Wormley" <sworml...@xxxxxxxxx> wrote in message
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Tom Potter wrote:

GPS signals can be jammed locally
as the pseudo-random codes used to
identify the satellites are known.
Satellite pseudo-random codes are not required
to jam GPS receivers, Potter. It doesn't take much
of a signal to saturate the RF sections of the
sensitive GPS receivers at the L-band frequencies.

Sammy, if I were trying to jam nearby GPS receivers,
I might use a transmitter tuned to the GPS band
to "saturate the RF sections",

L1 and L2 Navigation satellite Signal Power Budget

Parameter L1 P-Code L1 C/A-Code L2
P-Code





-----------------------------------------------------------------------
User minimum received power -163.0 dBw -160.0 dBw -166.0
dBw
Users linear antenna gain 3.0 dB 3.0 dB 3.0
dB
Free-space propagation loss 184.4 dB 184.4 dB 182.3
dB
Total atmospheric loss 2.0 dB 2.0 dB 2.0
dB
Polarization mismatch loss 3.4 dB 3.4 dB 4.4
dB
Required satellite EIRP +23.8 dBw +26.8 dBw +19.7
dBw
Satellite Antenna gain at 14.3° 13.5 dB 13.4 dB 11.5
dB
worst case Block II off-axis angle
Required minimum satellite antenna +10.3 dBw +13.4 dBw +8.2
dBw
input power 10.72W 21.88W
6.61W

Potter, since the signal is so weak at the GPS receiver antenna, a
single
small transmitter can "render unusable" all receivers over a large
area
(many hundreds of square km).

Here is one of the latest attempts to solve the GPS jamming problem.

==============================
United States Patent 7,250,903
McDowell July 31, 2007

GPS spoofer and repeater mitigation system using digital spatial nulling

* No, it's an attempt to solve a problem of GPS
* spoofing and repeating. See title.
*
* Exercise to Potter: What's the difference between
* "spoofing" and "jamming"?
*
* - Randy

Good point Randy.
The folks who got this patent
comprehend that digital communications systems
are extremely immune from "jamming",

* No, they aren't. As others are pointing out, it wouldn't
* take much power to jam the signal. GPS jamming
* is a major concern for DoD (US Dept of Defense).
*
* I'm just pointing out that this patent is not about
* jamming, but about spoofing which takes a weaker
*signal, designed to mimic the satellite's signal.

- Randy

Randy! Randy!
Do you read these references?

Excerpt from the patent.
================
"Description of the Related Art

In recent years, multi-element antenna systems have proven themselves to be
extremely effective at protecting GPS receivers from high power jamming.
High dynamic range systems with digital back-end processing, such as those
developed at Rockwell Collins, Inc., are capable of spatially nulling
jamming signals by as much as 60 dB while simultaneously maintaining good
antenna gain to desired signal sources.

Recently, however, there has been renewed interest in C/A code spoofers and
repeaters (meaconers). A spoofer is a broadcast signal intended to look like
a GPS satellite signal."

Randy, note that proper techniques are
"extremely effective at protecting GPS receivers from high power jamming",

but that there is a
"renewed interest in C/A code spoofers and repeaters (meaconers)."

An ad for a commercial "jammer" is listed below.
Note that it takes 1000 Milliwatts ( One watt)
of RF power to jam receivers about 50 feet away.

And note that the power spreads out as a function of
the square of the distance, so it would take
4 watts to jam a receiver 100 feet away,
16 watts to jam a receiver 200 feet away,
64 watts to jam a receiver 400 feet away, etc.

Ad for a GPS Jammer.
==============================
Big Power GPS Jammer
Description:
Total Output Power: 1000 Milliwatts
Effective distance: 0 to 15 metres (in optimum conditions)
===================

--
Tom Potter

http://home.earthlink.net/~tdp
http://notsocrazyideas.blogspot.com/




.

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