Empathy List Archives

JG

John Green

Mon, Nov 16, 2009 3:17 PM

All the discussion regarding jamming GPS has been very interesting. Because
it is spread spectrum, I always assumed it would be difficult to jam GPS.
The Monterey Bay incident indicates that it is extremely easy to jam GPS.
So, as soon as another project is out of the way, I intend to do some
experiments, more of a practical than scientific nature. I have a Z3801 and
Tbolt to start with. I would also like to experiment with a hand held and a
GPS enabled cellphone. To prevent unintended interference, signal levels
will have to be carefully controlled and transmission time will have to be
kept short. I want to try CW as well as modulations of varying types. Any
suggestions as to the most effective modulation type to try?

All the discussion regarding jamming GPS has been very interesting. Because it is spread spectrum, I always assumed it would be difficult to jam GPS. The Monterey Bay incident indicates that it is extremely easy to jam GPS. So, as soon as another project is out of the way, I intend to do some experiments, more of a practical than scientific nature. I have a Z3801 and Tbolt to start with. I would also like to experiment with a hand held and a GPS enabled cellphone. To prevent unintended interference, signal levels will have to be carefully controlled and transmission time will have to be kept short. I want to try CW as well as modulations of varying types. Any suggestions as to the most effective modulation type to try?

LJ

Lux, Jim (337C)

Mon, Nov 16, 2009 3:22 PM

On 11/16/09 7:17 AM, "John Green" wpxs472@gmail.com wrote:

All the discussion regarding jamming GPS has been very interesting. Because
it is spread spectrum, I always assumed it would be difficult to jam GPS.
The Monterey Bay incident indicates that it is extremely easy to jam GPS.
So, as soon as another project is out of the way, I intend to do some
experiments, more of a practical than scientific nature. I have a Z3801 and
Tbolt to start with. I would also like to experiment with a hand held and a
GPS enabled cellphone. To prevent unintended interference, signal levels
will have to be carefully controlled and transmission time will have to be
kept short. I want to try CW as well as modulations of varying types. Any
suggestions as to the most effective modulation type to try?

Do you want to jam during acquisition or during track?

Your cellphone probably has what's called an "assisted GPS" receiver, where
the cell system tells the receiver in the phone initial estimates of code
phase as well as which satellites are in view. That is, a lot of the
initial acquisition steps are already done. (it reduces nanojoules/fix
dramatically, and that's important in a cellphone.. And it makes the
receiver cheaper and that's important too)

Most inexpensive receivers use a single bit quantizer, so they're quite
vulnerable to a CW signal at the right frequency, because that will dominate
over the received spread signal, especially before code acquisition.

On 11/16/09 7:17 AM, "John Green" <wpxs472@gmail.com> wrote: > All the discussion regarding jamming GPS has been very interesting. Because > it is spread spectrum, I always assumed it would be difficult to jam GPS. > The Monterey Bay incident indicates that it is extremely easy to jam GPS. > So, as soon as another project is out of the way, I intend to do some > experiments, more of a practical than scientific nature. I have a Z3801 and > Tbolt to start with. I would also like to experiment with a hand held and a > GPS enabled cellphone. To prevent unintended interference, signal levels > will have to be carefully controlled and transmission time will have to be > kept short. I want to try CW as well as modulations of varying types. Any > suggestions as to the most effective modulation type to try? > Do you want to jam during acquisition or during track? Your cellphone probably has what's called an "assisted GPS" receiver, where the cell system tells the receiver in the phone initial estimates of code phase as well as which satellites are in view. That is, a lot of the initial acquisition steps are already done. (it reduces nanojoules/fix dramatically, and that's important in a cellphone.. And it makes the receiver cheaper and that's important too) Most inexpensive receivers use a single bit quantizer, so they're quite vulnerable to a CW signal at the right frequency, because that will dominate over the received spread signal, especially before code acquisition.

PK

Poul-Henning Kamp

Mon, Nov 16, 2009 3:53 PM

In message abec162c0911160717i2475eb64qe10f2123929594e2@mail.gmail.com, John
Green writes:

Any suggestions as to the most effective modulation type to try?

Pseudo-random 50Hz FSK ?

--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

In message <abec162c0911160717i2475eb64qe10f2123929594e2@mail.gmail.com>, John Green writes: >Any suggestions as to the most effective modulation type to try? Pseudo-random 50Hz FSK ? -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.

J

jmfranke@cox.net

Mon, Nov 16, 2009 5:36 PM

For testing, I would suggest using a directional coupler in the antenna lead to reduce the chances for unwanted radiation.

John WA4WDL

---- John Green wpxs472@gmail.com wrote:

All the discussion regarding jamming GPS has been very interesting. Because
it is spread spectrum, I always assumed it would be difficult to jam GPS.
The Monterey Bay incident indicates that it is extremely easy to jam GPS.
So, as soon as another project is out of the way, I intend to do some
experiments, more of a practical than scientific nature. I have a Z3801 and
Tbolt to start with. I would also like to experiment with a hand held and a
GPS enabled cellphone. To prevent unintended interference, signal levels
will have to be carefully controlled and transmission time will have to be
kept short. I want to try CW as well as modulations of varying types. Any
suggestions as to the most effective modulation type to try?

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For testing, I would suggest using a directional coupler in the antenna lead to reduce the chances for unwanted radiation. John WA4WDL ---- John Green <wpxs472@gmail.com> wrote: > All the discussion regarding jamming GPS has been very interesting. Because > it is spread spectrum, I always assumed it would be difficult to jam GPS. > The Monterey Bay incident indicates that it is extremely easy to jam GPS. > So, as soon as another project is out of the way, I intend to do some > experiments, more of a practical than scientific nature. I have a Z3801 and > Tbolt to start with. I would also like to experiment with a hand held and a > GPS enabled cellphone. To prevent unintended interference, signal levels > will have to be carefully controlled and transmission time will have to be > kept short. I want to try CW as well as modulations of varying types. Any > suggestions as to the most effective modulation type to try? > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

RA

Robert Atkinson

Mon, Nov 16, 2009 9:31 PM

Bit older but an interesting Thesis on jamming.
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA361736&Location=U2&doc=GetTRDoc.pdf
or google "Analysis of Radio Frequency Interference Effects on a Modern Coarse Acquisition Code Global Positioning System"

Robert G8RPI.

--- On Mon, 16/11/09, John Green wpxs472@gmail.com wrote:

From: John Green wpxs472@gmail.com
Subject: [time-nuts] Jamming GPS
To: time-nuts@febo.com
Date: Monday, 16 November, 2009, 15:17

All the discussion regarding jamming GPS has been very interesting. Because
it is spread spectrum, I always assumed it would be difficult to jam GPS.
The Monterey Bay incident indicates that it is extremely easy to jam GPS.
So, as soon as another project is out of the way, I intend to do some
experiments, more of a practical than scientific nature. I have a Z3801 and
Tbolt to start with. I would also like to experiment with a hand held and a
GPS enabled cellphone. To prevent unintended interference, signal levels
will have to be carefully controlled and transmission time will have to be
kept short. I want to try CW as well as modulations of varying types. Any
suggestions as to the most effective modulation type to try?

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Bit older but an interesting Thesis on jamming. http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA361736&Location=U2&doc=GetTRDoc.pdf or google "Analysis of Radio Frequency Interference Effects on a Modern Coarse Acquisition Code Global Positioning System" Robert G8RPI. --- On Mon, 16/11/09, John Green <wpxs472@gmail.com> wrote: From: John Green <wpxs472@gmail.com> Subject: [time-nuts] Jamming GPS To: time-nuts@febo.com Date: Monday, 16 November, 2009, 15:17 All the discussion regarding jamming GPS has been very interesting. Because it is spread spectrum, I always assumed it would be difficult to jam GPS. The Monterey Bay incident indicates that it is extremely easy to jam GPS. So, as soon as another project is out of the way, I intend to do some experiments, more of a practical than scientific nature. I have a Z3801 and Tbolt to start with. I would also like to experiment with a hand held and a GPS enabled cellphone. To prevent unintended interference, signal levels will have to be carefully controlled and transmission time will have to be kept short. I want to try CW as well as modulations of varying types. Any suggestions as to the most effective modulation type to try? _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

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Jamming GPS