date:20091115


b...@lysator.liu.se wrote:

John,


If a LORAN transmitter were destroyed by a terrorist team, a backup could
be in operation in hours. A damaged GPS system could easily take many
months or even years to fix.

-John


A LORAN site, with a several hundred meter high mast, a small house full
of transmitter, signal generation and Cs clock(s?)... on a remote
Norwegian island... would not be back online within a few hours after an
attack.


Regardless of location, it will take some time to restore functionality.
About a year maybe.

The LORAN-C station would reduce navigation in a certain area. However, 
since most interesting targets use GPS, it is a more interesting target.



GPS is supposed to work without _any_ terrestrial support for days or
weeks. I doubt that anyone can get something lethal for the SVs up in
orbit without making it very obvious who they are. GPS now has lots of hot
spare birds in orbit, that a instantly online with one or a few satellites
going bust.


The AutoNAV feature should keep it up for 180 days. It has never been 
used. Essentially, what if you wipe out the ground segment and needs to 
rebuild it. The ground segment points of GPS is fewer than the LORAN-C 
stations.


Firing rockets to down the birds is above the average terrorist budget 
and infrastructure. While not all 30 GPS birds needs to go down, a 
significant number of them needs to for a significant system impact. 
Downing a single of them is sufficient for the political effect, so that 
is more likely.


Using jammers is far more likely. It has been analyzed quite deeply.

It is not impossible to locate a GPS jammer. In Iraq, they had relative 
high power jammers and they where able to locate them and finally take 
them out.



That said, I think LORAN should be kept running as a backup, also with a
firm commitment that it WILL KEEP running for 10+ years, giving vendors a
reason to develop modern receivers.


The electronics needed to support LORAN-C and eLORAN is not very complex 
by todays measure. Could be integrated with a GPS receiver.


Cheers,
Magnus

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[time-nuts] FS HP103 Precision Crystal Reference

Nice looking, no mods.

$115 plus shipping from 75044.

Thank you!

Francesco Ledda
Garland, Texas




-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on
Behalf Of Magnus Danielson
Sent: Sunday, November 15, 2009 9:01 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] The Demise of LORAN (was Re: Reference
oscillator accuracy)


b...@lysator.liu.se wrote:
 John,

 If a LORAN transmitter were destroyed by a terrorist team, a backup could
 be in operation in hours. A damaged GPS system could easily take many
 months or even years to fix.

 -John

 A LORAN site, with a several hundred meter high mast, a small house full
 of transmitter, signal generation and Cs clock(s?)... on a remote
 Norwegian island... would not be back online within a few hours after an
 attack.

Regardless of location, it will take some time to restore functionality.
About a year maybe.

The LORAN-C station would reduce navigation in a certain area. However,
since most interesting targets use GPS, it is a more interesting target.

 GPS is supposed to work without _any_ terrestrial support for days or
 weeks. I doubt that anyone can get something lethal for the SVs up in
 orbit without making it very obvious who they are. GPS now has lots of hot
 spare birds in orbit, that a instantly online with one or a few satellites
 going bust.

The AutoNAV feature should keep it up for 180 days. It has never been
used. Essentially, what if you wipe out the ground segment and needs to
rebuild it. The ground segment points of GPS is fewer than the LORAN-C
stations.

Firing rockets to down the birds is above the average terrorist budget
and infrastructure. While not all 30 GPS birds needs to go down, a
significant number of them needs to for a significant system impact.
Downing a single of them is sufficient for the political effect, so that
is more likely.

Using jammers is far more likely. It has been analyzed quite deeply.

It is not impossible to locate a GPS jammer. In Iraq, they had relative
high power jammers and they where able to locate them and finally take
them out.

 That said, I think LORAN should be kept running as a backup, also with a
 firm commitment that it WILL KEEP running for 10+ years, giving vendors a
 reason to develop modern receivers.

The electronics needed to support LORAN-C and eLORAN is not very complex
by todays measure. Could be integrated with a GPS receiver.

Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

The bottom line is simple: the military don't need it, the FAA see no value
in it; the avionics industry has discontinued the manufacturing of LORAN
receivers years ago, the General Aviation community has bigger fish to fry
(fight user fees); the Europen talked in the past about using LORAN for
redundancy purposes, but never issued any concrete plans or requisitions.

For all above reasons, LORAN is going to go.

As a pilot, my personal experience about LORAN is mixed. Two times in heavy
IMC, using RNAV LORAN, the LORAN went out in crytical phases of flight. This
has never happened to me, with GPS.



-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on
Behalf Of Magnus Danielson
Sent: Sunday, November 15, 2009 9:01 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] The Demise of LORAN (was Re: Reference
oscillator accuracy)


b...@lysator.liu.se wrote:
 John,

 If a LORAN transmitter were destroyed by a terrorist team, a backup could
 be in operation in hours. A damaged GPS system could easily take many
 months or even years to fix.

 -John

 A LORAN site, with a several hundred meter high mast, a small house full
 of transmitter, signal generation and Cs clock(s?)... on a remote
 Norwegian island... would not be back online within a few hours after an
 attack.

Regardless of location, it will take some time to restore functionality.
About a year maybe.

The LORAN-C station would reduce navigation in a certain area. However,
since most interesting targets use GPS, it is a more interesting target.

 GPS is supposed to work without _any_ terrestrial support for days or
 weeks. I doubt that anyone can get something lethal for the SVs up in
 orbit without making it very obvious who they are. GPS now has lots of hot
 spare birds in orbit, that a instantly online with one or a few satellites
 going bust.

The AutoNAV feature should keep it up for 180 days. It has never been
used. Essentially, what if you wipe out the ground segment and needs to
rebuild it. The ground segment points of GPS is fewer than the LORAN-C
stations.

Firing rockets to down the birds is above the average terrorist budget
and infrastructure. While not all 30 GPS birds needs to go down, a
significant number of them needs to for a significant system impact.
Downing a single of them is sufficient for the political effect, so that
is more likely.

Using jammers is far more likely. It has been analyzed quite deeply.

It is not impossible to locate a GPS jammer. In Iraq, they had relative
high power jammers and they where able to locate them and finally take
them out.

 That said, I think LORAN should be kept running as a backup, also with a
 firm commitment that it WILL KEEP running for 10+ years, giving vendors a
 reason to develop modern receivers.

The electronics needed to support LORAN-C and eLORAN is not very complex
by todays measure. Could be integrated with a GPS receiver.

Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

2009-11-15 Thread Mike Monett

  J. Forster j...@quik.com wrote:

   I've read and heard from this forum as well as a number  of other
   sources that  GPS  can  be   easily  jammed.  What  makes  GPS so
   vulnerable? How can it be jammed?

   Signal strength.

   LORAN transmitters  put  out multi-hundred  KW  to  MegaWatt class
   pulses. Wiki  has a list. I would think a GPS bird  puts  out less
   than 100 Watts CW.

   Also, GPS  birds  are a LOT farther away,  especially  measured in
   wavelengths (much higher path loss)

   Those factors combine to make a huge difference in received power.

   It could well be over 100 dB.

   From what I've heard a GPS jammer smaller than a deck  of playing
   cards can  easily wipe out GPS w/in a mile or more for a  week or
   longer.

   John

  It should  be easy to locate a jammer. Go to the area where  the GPS
  signal is being jammed. Drive in some direction until the  signal is
  regained. Repeat to find three locations where the signal is lost.

  Three points define a circle. The diameter tells the strength of the
  jamming signal. The center defines the location.

  Once you are near the center, ordinary DF techniques  should quickly
  identify the source.

  For faster  response,  have  a number of  GPS  receivers  report the
  status of the GPS signal to a central location. This  would identify
  a moving jammer.

  It should also be possible to develop a GPS antenna with one or more
  nulls in the horizontal direction. Rotate the antenna until  the GPS
  signal is  regained.  The   null   points  to  the  jammer. Multiple
  receivers would  remove the ambiguity from antennas  with  more than
  one null.

  These techniques  should identify a jammer very quickly,  perhaps in
  hours or  minutes instead of weeks. I'm sure the  military  has some
  more advanced methods, as well as effective methods of  dealing with
  the threat.

  Mike Monett

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)


Francesco Ledda wrote:

The bottom line is simple: the military don't need it, the FAA see no value
in it; the avionics industry has discontinued the manufacturing of LORAN
receivers years ago, the General Aviation community has bigger fish to fry
(fight user fees); the Europen talked in the past about using LORAN for
redundancy purposes, but never issued any concrete plans or requisitions.

For all above reasons, LORAN is going to go.


The time for cutting the service will come eventually. While it has 
serviced us well, the use is not as heavy as previous years and it has 
essentially been replaced by GPS. It's sad to see it go, but in times 
when budget is tought good old systems gets killed. Eventually they need 
to. For those only having LORAN-C, the investment into a GPS receiver 
should not be too steep.


Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)


I guess the point you folks aren't getting is you can make a very
effective local GPS jammer that runs off of a 9V transistor radio battery,
and will last for several weeks.  It can be done for a total cost of
a few bucks per jammer search the web, the designs are out there.

Toss the GPS jammers indiscriminately around the landscape, and you put
GPS out of business for a very low cost.

-Chuck Harris

Mike Monett wrote:


  It should  be easy to locate a jammer. Go to the area where  the GPS
  signal is being jammed. Drive in some direction until the  signal is
  regained. Repeat to find three locations where the signal is lost.

  Three points define a circle. The diameter tells the strength of the
  jamming signal. The center defines the location.

  Once you are near the center, ordinary DF techniques  should quickly
  identify the source.



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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

 b...@lysator.liu.se wrote:
 John,

 If a LORAN transmitter were destroyed by a terrorist team, a backup
 could
 be in operation in hours. A damaged GPS system could easily take many
 months or even years to fix.

 -John

The military have air deployable radio trucks. A LORAN station could be
built into a few trailers, including generator, clocks, and transmitter.
There are also fielded deployable masts.

Such a station could be deployed rapidly. It would not have as powerful
signal as the original station, but would, IMO, be fully functional.

-John




 A LORAN site, with a several hundred meter high mast, a small house full
 of transmitter, signal generation and Cs clock(s?)... on a remote
 Norwegian island... would not be back online within a few hours after an
 attack.

 Regardless of location, it will take some time to restore functionality.
 About a year maybe.



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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

 John,

 If a LORAN transmitter were destroyed by a terrorist team, a backup could
 be in operation in hours. A damaged GPS system could easily take many
months or even years to fix.

 -John

 A LORAN site, with a several hundred meter high mast, a small house full
of transmitter, signal generation and Cs clock(s?)... on a remote
Norwegian island... would not be back online within a few hours after an
attack.

I think it'd still be a lot easier to replace quickly than GPS jammers
widely seeded.

What would happen if some rogue country started building mini-GPS jammers
and giving them to insurgents to randomly scatter around. A single donkey
could carry many hundreds?

Or suppose a jammer was built into a child's toy and ran intermittantly
off the toy's batteries and sold by the zillions at Walmart for Christmas?

 GPS is supposed to work without _any_ terrestrial support for days or
weeks. I doubt that anyone can get something lethal for the SVs up in
orbit without making it very obvious who they are. GPS now has lots of
hot spare birds in orbit, that a instantly online with one or a few
satellites going bust.

I've never suggested attacking the birds is a credible terrorist threat.
It is not, IMO.

 That said, I think LORAN should be kept running as a backup, also with a
firm commitment that it WILL KEEP running for 10+ years, giving vendors
a reason to develop modern receivers.

 --

Björn

IMO, GPS is much more vulnerable to a jamming attack and LORAN must be
maintained as a backup.

FWIW,
-John







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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

Thanks Chuck,

My point EXACTLY.

1. It's well within the capability of dozens of countries or organizations
or even individuals.

2. They are trivial to distribute widely, and could be piggy-backed onto
other things.

3. Given enough of them with random on-off cycles, you'd force a giant
game of Whak-A-Mole.

A guy in his basement could easily build 100 in a week given a design and
PCB layout. In another week he could scatter them all over a city, even if
travelling by bus. The whole operation would cost under a few thousand
dollars.

Furthermore, it would not be needed to kill all the GPS in an area, all
the time. Making it unreliable would likely be enough.

FWIW,
-John

==



 I guess the point you folks aren't getting is you can make a very
 effective local GPS jammer that runs off of a 9V transistor radio battery,
 and will last for several weeks.  It can be done for a total cost of
 a few bucks per jammer search the web, the designs are out there.

 Toss the GPS jammers indiscriminately around the landscape, and you put
 GPS out of business for a very low cost.

 -Chuck Harris

 Mike Monett wrote:

   It should  be easy to locate a jammer. Go to the area where  the GPS
   signal is being jammed. Drive in some direction until the  signal is
   regained. Repeat to find three locations where the signal is lost.

   Three points define a circle. The diameter tells the strength of the
   jamming signal. The center defines the location.

   Once you are near the center, ordinary DF techniques  should quickly
   identify the source.


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

2009-11-15 Thread Richard W. Solomon

After reading all the responses on this thread, all I can think
of is the numerous ideas you folks have given some whackjob out
there.

Keep up the good work.

73, Dick, W1KSZ

-Original Message-
From: Chuck Harris cfhar...@erols.com
Sent: Nov 15, 2009 9:51 AM
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Subject: Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator 
accuracy)

I guess the point you folks aren't getting is you can make a very
effective local GPS jammer that runs off of a 9V transistor radio battery,
and will last for several weeks.  It can be done for a total cost of
a few bucks per jammer search the web, the designs are out there.

Toss the GPS jammers indiscriminately around the landscape, and you put
GPS out of business for a very low cost.

-Chuck Harris

Mike Monett wrote:

   It should  be easy to locate a jammer. Go to the area where  the GPS
   signal is being jammed. Drive in some direction until the  signal is
   regained. Repeat to find three locations where the signal is lost.
 
   Three points define a circle. The diameter tells the strength of the
   jamming signal. The center defines the location.
 
   Once you are near the center, ordinary DF techniques  should quickly
   identify the source.


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

I just put jamming GPS into Google, and got about 348,000 hits.

-John




 After reading all the responses on this thread, all I can think
 of is the numerous ideas you folks have given some whackjob out
 there.

 Keep up the good work.

 73, Dick, W1KSZ

 -Original Message-
From: Chuck Harris cfhar...@erols.com
Sent: Nov 15, 2009 9:51 AM
To: Discussion of precise time and frequency measurement
 time-nuts@febo.com
Subject: Re: [time-nuts] The Demise of LORAN (was Re: Reference
 oscillator accuracy)

I guess the point you folks aren't getting is you can make a very
effective local GPS jammer that runs off of a 9V transistor radio
 battery,
and will last for several weeks.  It can be done for a total cost of
a few bucks per jammer search the web, the designs are out there.

Toss the GPS jammers indiscriminately around the landscape, and you put
GPS out of business for a very low cost.

-Chuck Harris

Mike Monett wrote:

   It should  be easy to locate a jammer. Go to the area where  the GPS
   signal is being jammed. Drive in some direction until the  signal is
   regained. Repeat to find three locations where the signal is lost.

   Three points define a circle. The diameter tells the strength of the
   jamming signal. The center defines the location.

   Once you are near the center, ordinary DF techniques  should quickly
   identify the source.


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

2009-11-15 Thread Scott A Sybert

Exposing vulnerabilities always make for a more secure product.  
 
Hiding known security risks or possible avenues of sabotage only creates a 
false sense of security.
 
I'd rather know how vulnerable GPS is and have paper maps  charts than have 
the false sense of security it's an untouchable system because it's high up in 
space or any other argument of redundancy, etc.
 
Bottom line is, talking about the possible vulnerabilities for technical 
purposes isn't giving the enemy any ideas they don't already have.
 
China shot down a weather satellite a few years ago testing a rocket.
 
You don't think there was an underlying message to that?  Believe me, The enemy 
has ideas AND capabilities we haven't even come close to covering.
 
And my opinion,  Maybe Obama should take one less flight to Europe talking down 
about his own nation and spend that 190M on supporting LORAN for the next 10 
years (obviously inflated flight costs but you get the picture)
 
Lets face it, the arugment about saving money shouldn't start on cancelling 
FUNCTIONAL and NECESSARY programs.
 
There's plenty of earmarks, bailouts and other waste that we could EASILY 
cancel to come up with the 190M required to keep this NAVIGATION system online 
another decade.
 
Just my two cents.
 
Regards,
Scott
CISSP.
 



From: time-nuts-boun...@febo.com on behalf of Richard W. Solomon
Sent: Sun 11/15/2009 12:26 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator 
accuracy)



After reading all the responses on this thread, all I can think
of is the numerous ideas you folks have given some whackjob out
there.

Keep up the good work.

73, Dick, W1KSZ

-Original Message-
From: Chuck Harris cfhar...@erols.com
Sent: Nov 15, 2009 9:51 AM
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Subject: Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator 
accuracy)

I guess the point you folks aren't getting is you can make a very
effective local GPS jammer that runs off of a 9V transistor radio battery,
and will last for several weeks.  It can be done for a total cost of
a few bucks per jammer search the web, the designs are out there.

Toss the GPS jammers indiscriminately around the landscape, and you put
GPS out of business for a very low cost.

-Chuck Harris

Mike Monett wrote:

   It should  be easy to locate a jammer. Go to the area where  the GPS
   signal is being jammed. Drive in some direction until the  signal is
   regained. Repeat to find three locations where the signal is lost.

   Three points define a circle. The diameter tells the strength of the
   jamming signal. The center defines the location.

   Once you are near the center, ordinary DF techniques  should quickly
   identify the source.


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)

Enough for what? To bug the heck out of a citizen suddenly unable to find his 
way to the movie theater?

Weapon systems and aircraft navigation  are unlikely to be affected by such a 
simple device on the ground, even if deployed in large quantity. Most of the 
stuff that really needs GPS has decent antennas that look up, not down.

Didier

 Sent from my BlackBerry Wireless thingy while I do 
other things... 

-Original Message-
From: J. Forster j...@quik.com
Date: Sun, 15 Nov 2009 09:23:12 
To: Discussion of precise time and frequency measurementtime-nuts@febo.com
Subject: Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator
 accuracy)

Thanks Chuck,

My point EXACTLY.

1. It's well within the capability of dozens of countries or organizations
or even individuals.

2. They are trivial to distribute widely, and could be piggy-backed onto
other things.

3. Given enough of them with random on-off cycles, you'd force a giant
game of Whak-A-Mole.

A guy in his basement could easily build 100 in a week given a design and
PCB layout. In another week he could scatter them all over a city, even if
travelling by bus. The whole operation would cost under a few thousand
dollars.

Furthermore, it would not be needed to kill all the GPS in an area, all
the time. Making it unreliable would likely be enough.

FWIW,
-John

==



 I guess the point you folks aren't getting is you can make a very
 effective local GPS jammer that runs off of a 9V transistor radio battery,
 and will last for several weeks.  It can be done for a total cost of
 a few bucks per jammer search the web, the designs are out there.

 Toss the GPS jammers indiscriminately around the landscape, and you put
 GPS out of business for a very low cost.

 -Chuck Harris

 Mike Monett wrote:

   It should  be easy to locate a jammer. Go to the area where  the GPS
   signal is being jammed. Drive in some direction until the  signal is
   regained. Repeat to find three locations where the signal is lost.

   Three points define a circle. The diameter tells the strength of the
   jamming signal. The center defines the location.

   Once you are near the center, ordinary DF techniques  should quickly
   identify the source.


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

In message 1078.12.6.201.222.1258304694.squir...@popacctsnew.quik.com, J. Fo
rster writes:

The military have air deployable radio trucks. A LORAN station could be
built into a few trailers, including generator, clocks, and transmitter.
There are also fielded deployable masts.

In fact, that is pretty much how the original LORAN was built...

There are some very good stories about this on:
http://www.loran-history.info/default.asp

Poul-Henning

-- 
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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

In message e1n9i6k-0005pl...@meow.febo.com, Mike Monett writes:

  It should  be easy to locate a jammer. Go to the area where  the GPS
  signal is being jammed. Drive in some direction until the  signal is
  regained. Repeat to find three locations where the signal is lost.

Experience has shown that this is far from as easy as that.

For one thing, you have no assurance that the jammer has isotropic
propagation and your local geometry  obstructions will determine
the subset of sats you have access to.

In military excercises, I have been told the average time to find
a jammer is on the order of many hours in an simulated urban
setting, due to propagation and access issues.

Poul-Henning

-- 
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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)


Chuck Harris wrote:

I guess the point you folks aren't getting is you can make a very
effective local GPS jammer that runs off of a 9V transistor radio battery,
and will last for several weeks.  It can be done for a total cost of
a few bucks per jammer search the web, the designs are out there.


We've known about it for years.


Toss the GPS jammers indiscriminately around the landscape, and you put
GPS out of business for a very low cost.


Exactly. You can manufacture hundreds of them and disperse them around.
Finding one of those is easy. Having many tens of them around makes it 
harder. Even if you find several of them, it will take the battery-time 
for the attack to go away completly. The strategy for such an attack and 
the strategy to deal with such an attack is a bit different.


A military receiver has about 40 dB better suppression just from the 
coding gain alone (30 dB for C/A and 70 dB for P(Y) if my memory serves 
me right). A number of other concerns also needs to be dealt with 
naturally, For obvious reasons alot of effort has been spent on covering 
this field, and if you are looking, there is alot of material out there.


The trouble is that civilian infrastructure does not have the 
countermeasures at the disposal to the military (US or allied forces).
If the civilian infrastructure was limited to a few handfull sites, the 
modern keying receivers intended for civilian usage would solve part of 
the problem, but there is a limit to how widely dispersed such receivers 
can be and also there is such a wide usage. Even lacking such 
counter-measures, the ability to just detect and warn about lacking 
reception conditions is less than acceptable in many systems. This 
details prohibits effective use of other reasnoble countermeasures.


Let's recall that interference also can be of non-intentional sort. 
Also, the huge use of GPS makes it a target for a certain operation, 
while unintentional targets may also suffer.


The trouble is that GPS receivers works too well. Install and forget.
Awareness of risk or even the ability to identify what sub-systems even 
depend on it is limited.


Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

In message 11603302.1258306016911.javamail.r...@elwamui-hound.atl.sa.earthlink
.net, Richard W. Solomon writes:

After reading all the responses on this thread, all I can think
of is the numerous ideas you folks have given some whackjob out
there.

I don't think you are up to date, all the whack-jobs have GPS
jammers already.

The first one was documented along with schematics and all in 
2600 magazine 15 years ago or so...

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)

How about in the area surrounding a major airport that has frequent low
visibility?

It is not necessary to jam GPS 100% 24/7. Just enough to cause real
concern about it's reliability would do huge damage.

How many missiles would be fired by Predator drones if 5 or 10% went wonky
and did big colateral damage?

-John

===


 Enough for what? To bug the heck out of a citizen suddenly unable to find
 his way to the movie theater?

 Weapon systems and aircraft navigation  are unlikely to be affected by
 such a simple device on the ground, even if deployed in large quantity.
 Most of the stuff that really needs GPS has decent antennas that look up,
 not down.

 Didier

  Sent from my BlackBerry Wireless thingy while I
 do other things...

 -Original Message-
 From: J. Forster j...@quik.com
 Date: Sun, 15 Nov 2009 09:23:12
 To: Discussion of precise time and frequency
 measurementtime-nuts@febo.com
 Subject: Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator
  accuracy)

 Thanks Chuck,

 My point EXACTLY.

 1. It's well within the capability of dozens of countries or organizations
 or even individuals.

 2. They are trivial to distribute widely, and could be piggy-backed onto
 other things.

 3. Given enough of them with random on-off cycles, you'd force a giant
 game of Whak-A-Mole.

 A guy in his basement could easily build 100 in a week given a design and
 PCB layout. In another week he could scatter them all over a city, even if
 travelling by bus. The whole operation would cost under a few thousand
 dollars.

 Furthermore, it would not be needed to kill all the GPS in an area, all
 the time. Making it unreliable would likely be enough.

 FWIW,
 -John

 ==



 I guess the point you folks aren't getting is you can make a very
 effective local GPS jammer that runs off of a 9V transistor radio
 battery,
 and will last for several weeks.  It can be done for a total cost of
 a few bucks per jammer search the web, the designs are out there.

 Toss the GPS jammers indiscriminately around the landscape, and you put
 GPS out of business for a very low cost.

 -Chuck Harris

 Mike Monett wrote:

   It should  be easy to locate a jammer. Go to the area where  the GPS
   signal is being jammed. Drive in some direction until the  signal is
   regained. Repeat to find three locations where the signal is lost.

   Three points define a circle. The diameter tells the strength of the
   jamming signal. The center defines the location.

   Once you are near the center, ordinary DF techniques  should quickly
   identify the source.


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

In message 4b004084.5060...@rubidium.dyndns.org, Magnus Danielson writes:
Chuck Harris wrote:

The trouble is that civilian infrastructure [...]

That's actually not the biggest problem, the biggest problem is access.

If you put a jammer at the top of a tall building (by RC helicopter ?)
getting up there to pick it up is non trivial for the people hunting 
it, they may need court orders to get access to service stairs etc.

Strictly speaking here in Denmark, the police would not have authority
to kick in a door to stop a GPS jammer, until the PTT has found
it a spectrum violation, warned the owner of the premises, possibly
in writing, if it is a rental building.

It is not obvious that a signal strong enough to jam GPS would
necessarily be found to be a spectrum violation in the first place.

Poul-Henning

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

 Chuck Harris wrote:
 I guess the point you folks aren't getting is you can make a very
 effective local GPS jammer that runs off of a 9V transistor radio
 battery,
 and will last for several weeks.  It can be done for a total cost of
 a few bucks per jammer search the web, the designs are out there.

 We've known about it for years.

 Toss the GPS jammers indiscriminately around the landscape, and you put
 GPS out of business for a very low cost.

 Exactly. You can manufacture hundreds of them and disperse them around.
 Finding one of those is easy. Having many tens of them around makes it
 harder. Even if you find several of them, it will take the battery-time
 for the attack to go away completly. The strategy for such an attack and
 the strategy to deal with such an attack is a bit different.

Not so.

You can easily buy a 1F or more capacitor. Take a small box, like a juice
box, put a few  solar cells on it and a 1F cap and jammer with a pseudo 
random on-off timer inside and deploy.

Bingo...  a headache for years.

-John





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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)

In message 1135.12.6.201.222.1258308021.squir...@popacctsnew.quik.com, J. Fo
rster writes:

How about in the area surrounding a major airport that has frequent low
visibility?

Airports are different, most airports are allowed to do whatever
it takes to eliminate interference which is a threat to aviation.

They also have the necessary kit to find and identify the jamming
signals.

Poul-Henning

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)

2009-11-15 Thread bg

How about in the area surrounding a major airport that has frequent low
visibility?

 Airports are different, most airports are allowed to do whatever
 it takes to eliminate interference which is a threat to aviation.

 They also have the necessary kit to find and identify the jamming
 signals.

 Poul-Henning

Then look at the weather forecast, get a supply of weather ballons and
release at a random shedule, from a wind direction chosen point. Your
jammers now have a good vehicle, to be above the receiver antenna. Very
hard to track and take out... I guess the airport soon would make sure
non-GPS navaids are well supported.

--

   Björn


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)

In message 49937.87.227.52.225.1258312766.squir...@webmail.lysator.liu.se, bg
@lysator.liu.se writes:

Then look at the weather forecast, get a supply of weather ballons and
release at a random shedule, from a wind direction chosen point. Your
jammers now have a good vehicle, to be above the receiver antenna. Very
hard to track and take out... I guess the airport soon would make sure
non-GPS navaids are well supported.

I'm not saying that GPS isn't easy jam-able, I'm saying airports are
hard targets for it.

Poul-Henning

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

2009-11-15 Thread Majdi S. Abbas

On Sun, Nov 15, 2009 at 11:37:11AM -0500, Mike Monett wrote:
   It should  be easy to locate a jammer. Go to the area where  the GPS
   signal is being jammed. Drive in some direction until the  signal is
   regained. Repeat to find three locations where the signal is lost.
 
   Three points define a circle. The diameter tells the strength of the
   jamming signal. The center defines the location.

And if the jammer is attached to, saY a radiosonde balloon or 
other light aircraft and the footprint covers most of the US?

Stop thinking terrestrially.

73,

Majdi, N0RMZ

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

In message 20091115193126.gb5...@puck.nether.net, Majdi S. Abbas writes:
On Sun, Nov 15, 2009 at 11:37:11AM -0500, Mike Monett wrote:

   And if the jammer is attached to, saY a radiosonde balloon or 
other light aircraft and the footprint covers most of the US?

It doesn't.

Hint: http://blogs.techrepublic.com.com/geekend/?p=372

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)

That would be extremely effective, and over a broad area, but then they will 
probably not run for weeks.

Didier

 Sent from my BlackBerry Wireless thingy while I do 
other things... 

-Original Message-
From: Majdi S. Abbas m...@latt.net
Date: Sun, 15 Nov 2009 12:31:26 
To: Discussion of precise time and frequency measurementtime-nuts@febo.com
Subject: Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator
 accuracy)

On Sun, Nov 15, 2009 at 11:37:11AM -0500, Mike Monett wrote:
   It should  be easy to locate a jammer. Go to the area where  the GPS
   signal is being jammed. Drive in some direction until the  signal is
   regained. Repeat to find three locations where the signal is lost.
 
   Three points define a circle. The diameter tells the strength of the
   jamming signal. The center defines the location.

And if the jammer is attached to, saY a radiosonde balloon or 
other light aircraft and the footprint covers most of the US?

Stop thinking terrestrially.

73,

Majdi, N0RMZ

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)


Didier Juges wrote:

Enough for what? To bug the heck out of a citizen suddenly unable to find his 
way to the movie theater?

Weapon systems and aircraft navigation  are unlikely to be affected by such a 
simple device on the ground, even if deployed in large quantity. Most of the 
stuff that really needs GPS has decent antennas that look up, not down.


They are affected, it is well covered, but the difference is the 
distance from the jammer until affected. It's a fairly well-understood 
problem and the difference between civilian and military receivers lies 
in signals, keying for access, bootstrapping and testing and 
counter-measures such as IMU.


Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)

In message 4b006929.3010...@rubidium.dyndns.org, Magnus Danielson writes:

distance from the jammer until affected. It's a fairly well-understood 
problem and the difference between civilian and military receivers lies 
in signals, keying for access, bootstrapping and testing and 
counter-measures such as IMU.

Not to mention clocks:  The more stable clock a GPS receiver has, the
harder it is to jam it, because the unspread bandwidth can be
much tighter.

Somebody showed a specially tuned GPS receiver, clocked from Cs to
be pretty much invulnerable to randomised jamming.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)


Given that I learned the techniques from a bunch of wack-jobs, I don't
think I have upped the learning curve much.

-Chuck

Richard W. Solomon wrote:

After reading all the responses on this thread, all I can think
of is the numerous ideas you folks have given some whackjob out
there.

Keep up the good work.

73, Dick, W1KSZ


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)

2009-11-15 Thread Robert Atkinson

There is also the use of directional antennas. Difficult to put your jammer 
between the Rx and the sat. 

--- On Sun, 15/11/09, Magnus Danielson mag...@rubidium.dyndns.org wrote:

From: Magnus Danielson mag...@rubidium.dyndns.org
Subject: Re: [time-nuts] The Demise of LORAN (was Re: Reference 
oscillatoraccuracy)
To: did...@cox.net, Discussion of precise time and frequency measurement 
time-nuts@febo.com
Date: Sunday, 15 November, 2009, 20:48

Didier Juges wrote:
 Enough for what? To bug the heck out of a citizen suddenly unable to find his 
 way to the movie theater?

 Weapon systems and aircraft navigation  are unlikely to be affected by such a 
 simple device on the ground, even if deployed in large quantity. Most of the 
 stuff that really needs GPS has decent antennas that look up, not down.

They are affected, it is well covered, but the difference is the distance from 
the jammer until affected. It's a fairly well-understood problem and the 
difference between civilian and military receivers lies in signals, keying for 
access, bootstrapping and testing and counter-measures such as IMU.

Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)


Robert Atkinson wrote:
There is also the use of directional antennas. Difficult to put your jammer between the Rx and the sat. 


Actually, that doesn't help much in a multiple jammer scenario.

The directional antenna needs to have their directional lobes towards 
each sat being tracked. If you try put the nulls towards the jammers 
then you need to have a fair knowledge of where it is. If you direct the 
loop, the side-loobs needs to be sufficiently suppressed. A single 
jammer and a fair idea of the heading will work, but it becomes complex 
and in the end you need more and more antennas to handle more jammers.


Also, recall that you need good dynamics on all the antenna frontends.

You can handle it, but it isn't compact and neat as you are used to.

Directional antennas gives some additional gain, but to a limit. It 
comes at a price. A rather high price compared to many other 
countermeasures. It only fit some few uses.


Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)

2009-11-15 Thread Bruce Rahn


Magnus Danielson wrote:
The directional antenna needs to have their directional lobes towards 
each sat being tracked. If you try put the nulls towards the jammers 
then you need to have a fair knowledge of where it is. If you direct 
the loop, the side-loobs needs to be sufficiently suppressed. A single 
jammer and a fair idea of the heading will work, but it becomes 
complex and in the end you need more and more antennas to handle more 
jammers. 
Ah...you really don't need any a prori knowledge of the location of a 
jammer. 

A little reading on adaptive antenna technology as applied to GPS will 
throw light on my comment and is also some interesting reading.  This 
would be a starting point: 
http://www.raytheon.com/businesses/stellent/groups/sas/documents/content/cms04_022900.pdf  



Bruce, WB9ANQ

--
Bruce Rahn

Wisdom has two parts:
1.  having a lot to say; and
2.  not saying it!



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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

What makes you think it needs to be CW, and cannot be pulsed and
chirped?

All it has to do is confuse the receiver enough so that you can't
trust its readings.

-Chuck

Mike Monett wrote:

Chuck Harris cfhar...@erols.com wrote:

I guess the point you folks aren't getting is you can make a very
effective local GPS jammer that runs off of a 9V transistor radio
battery, and will last for several weeks. It can be done for a
total cost of a few bucks per jammer search the web, the
designs are out there.

Toss the GPS jammers indiscriminately around the landscape, and
you put GPS out of business for a very low cost.

-Chuck Harris

I'm not so sure that would be very effective. A typical 9v alkaline
contains about 900 milliamp/hours at low current drain.

Two weeks is 24 * 7 * 2 = 336 hrs. Assuming 100% efficiency, the
battery would supply 0.9 / 336 = 0.00267A, or 0.024 watt, not
including the drop in voltage after the first few dozen hours.

There are quite a few commercial jammers designed specifically to
jam GPS signals. These are extremely illegal, but they do give some
idea of the range that could be expected.

Below is a list of the specified range and power. I calculate the
highest ratio to get the meters per watt.

GMW12 Cellular GPS L1 Jammer

Block cellular signals and GPS L1 system in the same time

Jamming Range : Average 40 meters radius
Output Power : Total 6.5 Watt

ratio : 40/6.5 = 6.15 meters/watt

http://www.tayx.co.uk/gmw12-gps-mobile-jammer.html

KYG0014 Fixed Jammer

Output Power : 2000mw
Jamming Range : 15~20 meters

ratio : 20/2 = 10 meters/watt

http://www.alibaba.com/product-gs/204091726/Fixed_GPS_jammer.html

KYG0017 Powerful GPS signal jammer

Output power : 25W
Range: radius 100-300meters

ratio : 300 / 25 = 12 meters/watt

http://www.alibaba.com/product-gs/213377763/Powerful_GPS_signal_jammer.html

KYG0013 Car GPS jammer

Output power : 800mW
Range: radius 10-15 meters

ratio : 15 / 0.8 = 8.75 meters/watt

http://www.alibaba.com/product-gs/204037628/KYG0013_Car_GPS_jammer.html

KYP0050 Handheld GPS/GSM signal Jammer / blocker

output power : 300mw
jamming range : 2~10 meters

ratio : 10 / 0.3 = 33.33 meters/watt

http://www.alibaba.com/product-gs/206648711/KYP0050_Handheld_GPS_GSM_signal_Jammer_blocker.html

The average ratio is:

(33.33 + 8.75 + 8.75 + 12 + 10 + 6.15) / 6 = 13.16 meters/watt.

The highest claimed performance is the KYP0050, with 33 meters/watt.

Assuming the 9V battery jammer has 100% RF efficiency and equal
ratio, the jamming range would be 33.33 * 0.024 = 0.799 meters or
about 2.62 feet.

However, a jammer would require crystal control to stay on
frequency. There are no crystals for L1, so a multiplier would be
needed. The actual power output would be much lower, so the range
would be much less.

Another example, a 1500mAh rechargable pocket jammer has a 5 meter
range, and only lasts 2~3 hrs:

GMT04 Pocket GPS Jammer

Jaming Range : Average 5 meters radius
Current Voltage : 200mA DC12V / AC120~140V
Battery : 1,500mAh

battery life 2~3 hours, recharge needs 3~4 hours

http://www.tayx.co.uk/gmt04-pocket-gps-jammer.html

So a 9V transistor radio battery jammer doesn't seem like it would
present much of a danger.

Mike Monett

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Re: [time-nuts] The Demise of LORAN (was Re: Referenceoscillatoraccuracy)

2009-11-15 Thread phil


Didier Juges wrote:
Enough for what? To bug the heck out of a citizen suddenly unable to find 
his way to the movie theater?


Weapon systems and aircraft navigation are unlikely to be affected by such 
a simple device on the ground, even if deployed in large quantity. Most of 
the stuff that really needs GPS has decent antennas that look up, not 
down.


They are affected, it is well covered, but the difference is the distance 
from the jammer until affected. It's a fairly well-understood problem and 
the difference between civilian and military receivers lies in signals, 
keying for access, bootstrapping and testing and counter-measures such as 
IMU.


Cheers,
Magnus


Possibly the two largest threats are being overlooked in this discussion. 
The US, Russia, and now China has numerous, possibly in the hundreds of 
clandestine truck sized satellites. Allot thought to weigh in at 8 to 10 
thousand pounds and some such as launched by the space shuttle to weigh in 
at 50,000 pounds up there now. Are they for communications, super-duper 
eyeballs, overgrown pea-shooters/laser guns, jammers, another positioning 
technology, or all of the above? Perhaps the ability to take out the various 
gps and other satellite systems exists now with the push of a button.


Should systems go down under those circumstances, finding the nearest 
Starbucks using gps may be the least of our worries.


Second and perhaps the real threat is a series of unprecedented solar storms 
or other unknown space based threats. That could conceivably render most of 
the satellites useless. I would think that ground based backup of all 
satellite systems would be mandatory.


Phil


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)


Bruce Rahn wrote:

Magnus Danielson wrote:
The directional antenna needs to have their directional lobes towards 
each sat being tracked. If you try put the nulls towards the jammers 
then you need to have a fair knowledge of where it is. If you direct 
the loop, the side-loobs needs to be sufficiently suppressed. A single 
jammer and a fair idea of the heading will work, but it becomes 
complex and in the end you need more and more antennas to handle more 
jammers. 
Ah...you really don't need any a prori knowledge of the location of a 
jammer.
A little reading on adaptive antenna technology as applied to GPS will 
throw light on my comment and is also some interesting reading.  This 
would be a starting point: 
http://www.raytheon.com/businesses/stellent/groups/sas/documents/content/cms04_022900.pdf  


You can use different strategies yes. I was unclear on that.

Either you know the direction and then you can optimize for that or you 
just use the power of multiple antennas to create individual lobes for 
each receiver channels. You can balance lobe-gain to sat to that of the 
offender for best suppression. Setting lobes for each sat does not need 
the direction info on the jammer.


That link does not provide as much information as a number of online 
articles on directional antennas giving much more detail.


Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)


Chuck,

Chuck Harris wrote:

What makes you think it needs to be CW, and cannot be pulsed and
chirped?


May I roll in a noise jammer into the debate?


All it has to do is confuse the receiver enough so that you can't
trust its readings.


Depends on the goal. For some strategies, blackout is the goal, for some 
getting the readings go haywire every once in a while suffice.


Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

2009-11-15 Thread Mike Monett

Chuck Harris cfhar...@erols.com wrote:

Toss the GPS jammers indiscriminately around the landscape, and
you put GPS out of business for a very low cost.

-Chuck Harris

I'm not so sure that would be very effective. A typical 9v alkaline
contains about 900 milliamp/hours at low current drain.

Two weeks is 24 * 7 * 2 = 336 hrs. Assuming 100% efficiency, the
battery would supply 0.9 / 336 = 0.00267A, or 0.024 watt, not
including the drop in voltage after the first few dozen hours.

There are quite a few commercial jammers designed specifically to
jam GPS signals. These are extremely illegal, but they do give some
idea of the range that could be expected.

Below is a list of the specified range and power. I calculate the
highest ratio to get the meters per watt.

GMW12 Cellular GPS L1 Jammer

Block cellular signals and GPS L1 system in the same time

Jamming Range : Average 40 meters radius
Output Power : Total 6.5 Watt

ratio : 40/6.5 = 6.15 meters/watt

http://www.tayx.co.uk/gmw12-gps-mobile-jammer.html

KYG0014 Fixed Jammer

Output Power : 2000mw
Jamming Range : 15~20 meters

ratio : 20/2 = 10 meters/watt

http://www.alibaba.com/product-gs/204091726/Fixed_GPS_jammer.html

KYG0017 Powerful GPS signal jammer

Output power : 25W
Range: radius 100-300meters

ratio : 300 / 25 = 12 meters/watt

http://www.alibaba.com/product-gs/213377763/Powerful_GPS_signal_jammer.html

KYG0013 Car GPS jammer

Output power : 800mW
Range: radius 10-15 meters

ratio : 15 / 0.8 = 8.75 meters/watt

http://www.alibaba.com/product-gs/204037628/KYG0013_Car_GPS_jammer.html

KYP0050 Handheld GPS/GSM signal Jammer / blocker

output power : 300mw
jamming range : 2~10 meters

ratio : 10 / 0.3 = 33.33 meters/watt

http://www.alibaba.com/product-gs/206648711/KYP0050_Handheld_GPS_GSM_signal_Jammer_blocker.html

The average ratio is:

(33.33 + 8.75 + 8.75 + 12 + 10 + 6.15) / 6 = 13.16 meters/watt.

The highest claimed performance is the KYP0050, with 33 meters/watt.

Assuming the 9V battery jammer has 100% RF efficiency and equal
ratio, the jamming range would be 33.33 * 0.024 = 0.799 meters or
about 2.62 feet.

Another example, a 1500mAh rechargable pocket jammer has a 5 meter
range, and only lasts 2~3 hrs:

GMT04 Pocket GPS Jammer

Jaming Range : Average 5 meters radius
Current Voltage : 200mA DC12V / AC120~140V
Battery : 1,500mAh

battery life 2~3 hours, recharge needs 3~4 hours

http://www.tayx.co.uk/gmt04-pocket-gps-jammer.html

So a 9V transistor radio battery jammer doesn't seem like it would
present much of a danger.

Mike Monett

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)

In message 4b00796d.6030...@rubidium.dyndns.org, Magnus Danielson writes:
Robert Atkinson wrote:

The directional antenna needs to have their directional lobes towards 
each sat being tracked. If you try put the nulls towards the jammers 
then you need to have a fair knowledge of where it is.

The phased array antennas does not operate in CW mode.

Once you have sat lock, you can operate the antennas in time-gate
mode, and only sampling each bird in a very narrow time window 
frequency band around the code-sign-change event and doppler
frequency.

That still does not reduce your antenna to a single beam, certainly
not if you only have 7 elements in 2D config, but for any moving
platform, that will make the 'sidelopes' swinging all over the
place, thus attenuating the jammer but not the intended bird.

And yes, this is not simple, but 97W ought to do it.

For a fixed location receiver, Pos-Hold mode is pretty efficient,
in particular if running of a known stable clock.

Poul-Henning

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@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.

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)


Magnus Danielson wrote:

Chuck,

Chuck Harris wrote:

What makes you think it needs to be CW, and cannot be pulsed and
chirped?


May I roll in a noise jammer into the debate?


Absolutely!  They can be extremely power efficient.  Raise the noise
floor in the vicinity of the receiver, and it is all done.

Probably the easiest solution would be to take a PN source and use it
to drive a pulser that pulses a chirp oscillator.  If you are feeling
really polite, you could put a bandpass filter on the thing to protect
other services.


All it has to do is confuse the receiver enough so that you can't
trust its readings.


Depends on the goal. For some strategies, blackout is the goal, for some 
getting the readings go haywire every once in a while suffice.


Agreed!

My 9V battery suggestion was for a localized blackout device.  You only
have to make the receiver question each satellite's signal often enough
for it to rule it out.  No way is CW necessary, or even desirable.

As John suggested, someone (say the Chinese) could put these things in
battery operated stuffed animals, and set them up to jam a little bit
now and then.  After Xmas, the GPS landscape would be littered with these
little stealth jammers, and willing supplicants to replace their batteries.

-Chuck

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

Or even into MP3 players, iPods, laptops, or cell phones. Then they'd
wander all over the place too. With the latter two hosts, they could even
be controlled remotely and even be fairly powerful. Would you notice
having to recharge your battery a bit more often?

-John

===


 Magnus Danielson wrote:
 Chuck,

 Chuck Harris wrote:
 What makes you think it needs to be CW, and cannot be pulsed and
 chirped?

 May I roll in a noise jammer into the debate?

 Absolutely!  They can be extremely power efficient.  Raise the noise
 floor in the vicinity of the receiver, and it is all done.

 Probably the easiest solution would be to take a PN source and use it
 to drive a pulser that pulses a chirp oscillator.  If you are feeling
 really polite, you could put a bandpass filter on the thing to protect
 other services.

 All it has to do is confuse the receiver enough so that you can't
 trust its readings.

 Depends on the goal. For some strategies, blackout is the goal, for some
 getting the readings go haywire every once in a while suffice.

 Agreed!

 My 9V battery suggestion was for a localized blackout device.  You only
 have to make the receiver question each satellite's signal often enough
 for it to rule it out.  No way is CW necessary, or even desirable.

 As John suggested, someone (say the Chinese) could put these things in
 battery operated stuffed animals, and set them up to jam a little bit
 now and then.  After Xmas, the GPS landscape would be littered with these
 little stealth jammers, and willing supplicants to replace their
 batteries.

 -Chuck

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)


Considering that the GPS antenna in aircrafts is mounted on top of fuselage,
and that its radiation pattern is upward, it seems that a ground jammer will
have an uphill battle.


-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on
Behalf Of J. Forster
Sent: Sunday, November 15, 2009 6:28 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] The Demise of LORAN (was Re: Reference
oscillator accuracy)


Or even into MP3 players, iPods, laptops, or cell phones. Then they'd
wander all over the place too. With the latter two hosts, they could even
be controlled remotely and even be fairly powerful. Would you notice
having to recharge your battery a bit more often?

-John

===


 Magnus Danielson wrote:
 Chuck,

 Chuck Harris wrote:
 What makes you think it needs to be CW, and cannot be pulsed and
 chirped?

 May I roll in a noise jammer into the debate?

 Absolutely!  They can be extremely power efficient.  Raise the noise
 floor in the vicinity of the receiver, and it is all done.

 Probably the easiest solution would be to take a PN source and use it
 to drive a pulser that pulses a chirp oscillator.  If you are feeling
 really polite, you could put a bandpass filter on the thing to protect
 other services.

 All it has to do is confuse the receiver enough so that you can't
 trust its readings.

 Depends on the goal. For some strategies, blackout is the goal, for some
 getting the readings go haywire every once in a while suffice.

 Agreed!

 My 9V battery suggestion was for a localized blackout device.  You only
 have to make the receiver question each satellite's signal often enough
 for it to rule it out.  No way is CW necessary, or even desirable.

 As John suggested, someone (say the Chinese) could put these things in
 battery operated stuffed animals, and set them up to jam a little bit
 now and then.  After Xmas, the GPS landscape would be littered with these
 little stealth jammers, and willing supplicants to replace their
 batteries.

 -Chuck

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)


Chuck Harris wrote:

Magnus Danielson wrote:

Chuck,

Chuck Harris wrote:

What makes you think it needs to be CW, and cannot be pulsed and
chirped?


May I roll in a noise jammer into the debate?


Absolutely!  They can be extremely power efficient.  Raise the noise
floor in the vicinity of the receiver, and it is all done.

Probably the easiest solution would be to take a PN source and use it
to drive a pulser that pulses a chirp oscillator.  If you are feeling
really polite, you could put a bandpass filter on the thing to protect
other services.


The schematic out there is a PN source feeding an OCXO and then 
amplified. Crystal loop to keep fairly centered. More or less the same 
as personalized phone jammers do. Very simple design.



All it has to do is confuse the receiver enough so that you can't
trust its readings.


Depends on the goal. For some strategies, blackout is the goal, for 
some getting the readings go haywire every once in a while suffice.


Agreed!

My 9V battery suggestion was for a localized blackout device.  You only
have to make the receiver question each satellite's signal often enough
for it to rule it out.  No way is CW necessary, or even desirable.


True.


As John suggested, someone (say the Chinese) could put these things in
battery operated stuffed animals, and set them up to jam a little bit
now and then.  After Xmas, the GPS landscape would be littered with these
little stealth jammers, and willing supplicants to replace their batteries.


Well, then you have to consider what the potential gain would be from 
such an attack. I fail to see the upside of that particular scenario. It 
would draw the attention over to them and in a field I think they rather 
stay calm about. Their ability to pull it off as such should not be 
doubted, but their resoning for it. Rather inefficient actually.


Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

Even 10 KM is pretty useful. If the thing were solar powered with a
supercap battery it could easly transmit for say 2 minutes per hour w/
significant power. It'd be hard to find if the on times were generated by
a multiple fedback CMOS shift register.

-John

Mike

Instead of relying on the dubious claims of those marketing an extremely
inefficient jammer it would be better to actually do some simple
calculations.

Typical commercial receivers stop tracking with a Jam to signal ratio of
not more than 60dB or so:
http://www.gpsworld.com/gps/jamming-gps-778

The input signal level at the receiver input is around -160dBW.

A 1W ERP source with an isotropic hemispheric radiation pattern will
exceed the the required jamming signal strength for distances less than
several tens of kilometers.

This estimate is consistent with the fact that LO parasitic radiation
from TV systems on boats have been known to jam GPS for distances of
several kilometers.

Bruce

Mike Monett wrote:
Chuck Harriscfhar...@erols.com wrote:

Toss the GPS jammers indiscriminately around the landscape, and
you put GPS out of business for a very low cost.

-Chuck Harris

I'm not so sure that would be very effective. A typical 9v alkaline
contains about 900 milliamp/hours at low current drain.

Two weeks is 24 * 7 * 2 = 336 hrs. Assuming 100% efficiency, the
battery would supply 0.9 / 336 = 0.00267A, or 0.024 watt, not
including the drop in voltage after the first few dozen hours.

There are quite a few commercial jammers designed specifically to
jam GPS signals. These are extremely illegal, but they do give some
idea of the range that could be expected.

Below is a list of the specified range and power. I calculate the
highest ratio to get the meters per watt.

GMW12 Cellular GPS L1 Jammer

Block cellular signals and GPS L1 system in the same time

Jamming Range : Average 40 meters radius
Output Power : Total 6.5 Watt

ratio : 40/6.5 = 6.15 meters/watt

http://www.tayx.co.uk/gmw12-gps-mobile-jammer.html

KYG0014 Fixed Jammer

Output Power : 2000mw
Jamming Range : 15~20 meters

ratio : 20/2 = 10 meters/watt

http://www.alibaba.com/product-gs/204091726/Fixed_GPS_jammer.html

KYG0017 Powerful GPS signal jammer

Output power : 25W
Range: radius 100-300meters

ratio : 300 / 25 = 12 meters/watt

http://www.alibaba.com/product-gs/213377763/Powerful_GPS_signal_jammer.html

KYG0013 Car GPS jammer

Output power : 800mW
Range: radius 10-15 meters

ratio : 15 / 0.8 = 8.75 meters/watt

http://www.alibaba.com/product-gs/204037628/KYG0013_Car_GPS_jammer.html

KYP0050 Handheld GPS/GSM signal Jammer / blocker

output power : 300mw
jamming range : 2~10 meters

ratio : 10 / 0.3 = 33.33 meters/watt

http://www.alibaba.com/product-gs/206648711/KYP0050_Handheld_GPS_GSM_signal_Jammer_blocker.html

The average ratio is:

(33.33 + 8.75 + 8.75 + 12 + 10 + 6.15) / 6 = 13.16 meters/watt.

The highest claimed performance is the KYP0050, with 33 meters/watt.

Assuming the 9V battery jammer has 100% RF efficiency and equal
ratio, the jamming range would be 33.33 * 0.024 = 0.799 meters or
about 2.62 feet.

Another example, a 1500mAh rechargable pocket jammer has a 5 meter
range, and only lasts 2~3 hrs:

GMT04 Pocket GPS Jammer

Jaming Range : Average 5 meters radius
Current Voltage : 200mA DC12V / AC120~140V
Battery : 1,500mAh

battery life 2~3 hours, recharge needs 3~4 hours

http://www.tayx.co.uk/gmt04-pocket-gps-jammer.html

So a 9V transistor radio battery jammer doesn't seem like it would
present much of a danger.

Mike Monett

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

2009-11-15 Thread Mike Monett

Chuck Harris cfhar...@erols.com wrote:

What makes you think it needs to be CW, and cannot be pulsed and
chirped?

All it has to do is confuse the receiver enough so that you can't
trust its readings.

-Chuck

I said nothing about the type of modulation. The equipment I listed is
designed specifically to disrupt GPS. Presumably they use whatever
modulation method that gives the best results.

However, GPS is spread-spectrum, so it  inherently rejects noise that is
not correlated with the satellite signal. This means effective jamming
requires a lot more power than is available from a 9V transistor radio
battery, and even then, the range is only a few meters.

I made an error in calculating the average range per watt. The original
shows 8.75 meters/watt twice:

  (33.33 + 8.75 + 8.75 + 12 + 10 + 6.15) / 6 = 13.16 meters/watt.

It should be
  
  (33.33 + 8.75 + 12 + 10 + 6.15) / 5 = 14.046 meters/watt.

This does not affect the conclusion, which is it takes a lot more power to
disrupt GPS than it first appears. Putting jammers in Christmas toys would
accomplish little except to drain the batteries faster.

Mike Monett

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

2009-11-15 Thread Hal Murray

  Jamming Range : Average 40 meters radius
  Output Power  : Total 6.5 Watt

  ratio : 40/6.5 = 6.15 meters/watt

Isn't received power 1/R-squared?

I think those calculations should be radius-squared/watts


I find it interesting that the products designed as jammers have ranges of 
only a few 10s of meters while a recent message here said 1/2 mile from a 
digital-radio link that was transmitting on 315 MHz.  (aka designed for 
something else rather than as a jammer)

Similarly, the Monterey Bay jammer wasn't trying to be a jammer, and it wiped 
out a huge area.



-- 
These are my opinions, not necessarily my employer's.  I hate spam.




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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

2009-11-15 Thread Bruce Griffiths

Mike

Instead of relying on the dubious claims of those marketing an extremely
inefficient jammer it would be better to actually do some simple
calculations.

Typical commercial receivers stop tracking with a Jam to signal ratio of
not more than 60dB or so:

http://www.gpsworld.com/gps/jamming-gps-778

The input signal level at the receiver input is around -160dBW.

A 1W ERP source with an isotropic hemispheric radiation pattern will
exceed the the required jamming signal strength for distances less than
several tens of kilometers.

This estimate is consistent with the fact that LO parasitic radiation
from TV systems on boats have been known to jam GPS for distances of
several kilometers.

Bruce

Mike Monett wrote:

Chuck Harriscfhar...@erols.com wrote:

Toss the GPS jammers indiscriminately around the landscape, and
you put GPS out of business for a very low cost.

-Chuck Harris

I'm not so sure that would be very effective. A typical 9v alkaline
contains about 900 milliamp/hours at low current drain.

Two weeks is 24 * 7 * 2 = 336 hrs. Assuming 100% efficiency, the
battery would supply 0.9 / 336 = 0.00267A, or 0.024 watt, not
including the drop in voltage after the first few dozen hours.

There are quite a few commercial jammers designed specifically to
jam GPS signals. These are extremely illegal, but they do give some
idea of the range that could be expected.

Below is a list of the specified range and power. I calculate the
highest ratio to get the meters per watt.

GMW12 Cellular GPS L1 Jammer

Block cellular signals and GPS L1 system in the same time

Jamming Range : Average 40 meters radius
Output Power : Total 6.5 Watt

ratio : 40/6.5 = 6.15 meters/watt

http://www.tayx.co.uk/gmw12-gps-mobile-jammer.html

KYG0014 Fixed Jammer

Output Power : 2000mw
Jamming Range : 15~20 meters

ratio : 20/2 = 10 meters/watt

http://www.alibaba.com/product-gs/204091726/Fixed_GPS_jammer.html

KYG0017 Powerful GPS signal jammer

Output power : 25W
Range: radius 100-300meters

ratio : 300 / 25 = 12 meters/watt

http://www.alibaba.com/product-gs/213377763/Powerful_GPS_signal_jammer.html

KYG0013 Car GPS jammer

Output power : 800mW
Range: radius 10-15 meters

ratio : 15 / 0.8 = 8.75 meters/watt

http://www.alibaba.com/product-gs/204037628/KYG0013_Car_GPS_jammer.html

KYP0050 Handheld GPS/GSM signal Jammer / blocker

output power : 300mw
jamming range : 2~10 meters

ratio : 10 / 0.3 = 33.33 meters/watt

http://www.alibaba.com/product-gs/206648711/KYP0050_Handheld_GPS_GSM_signal_Jammer_blocker.html

The average ratio is:

(33.33 + 8.75 + 8.75 + 12 + 10 + 6.15) / 6 = 13.16 meters/watt.

The highest claimed performance is the KYP0050, with 33 meters/watt.

Assuming the 9V battery jammer has 100% RF efficiency and equal
ratio, the jamming range would be 33.33 * 0.024 = 0.799 meters or
about 2.62 feet.

Another example, a 1500mAh rechargable pocket jammer has a 5 meter
range, and only lasts 2~3 hrs:

GMT04 Pocket GPS Jammer

Jaming Range : Average 5 meters radius
Current Voltage : 200mA DC12V / AC120~140V
Battery : 1,500mAh

battery life 2~3 hours, recharge needs 3~4 hours

http://www.tayx.co.uk/gmt04-pocket-gps-jammer.html

So a 9V transistor radio battery jammer doesn't seem like it would
present much of a danger.

Mike Monett

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

See my earlier post. Briefly:

Antennas do not have an infinite front-to-back ratio. (40 dB)

The path loss from a surface jammer to a plane (10 miles) is many, many dB
less than from plane to bird (15,000 miles).

-John





 Considering that the GPS antenna in aircrafts is mounted on top of
 fuselage,
 and that its radiation pattern is upward, it seems that a ground jammer
 will
 have an uphill battle.


 -Original Message-
 From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on
 Behalf Of J. Forster
 Sent: Sunday, November 15, 2009 6:28 PM
 To: Discussion of precise time and frequency measurement
 Subject: Re: [time-nuts] The Demise of LORAN (was Re: Reference
 oscillator accuracy)


 Or even into MP3 players, iPods, laptops, or cell phones. Then they'd
 wander all over the place too. With the latter two hosts, they could even
 be controlled remotely and even be fairly powerful. Would you notice
 having to recharge your battery a bit more often?

 -John

 ===


 Magnus Danielson wrote:
 Chuck,

 Chuck Harris wrote:
 What makes you think it needs to be CW, and cannot be pulsed and
 chirped?

 May I roll in a noise jammer into the debate?

 Absolutely!  They can be extremely power efficient.  Raise the noise
 floor in the vicinity of the receiver, and it is all done.

 Probably the easiest solution would be to take a PN source and use it
 to drive a pulser that pulses a chirp oscillator.  If you are feeling
 really polite, you could put a bandpass filter on the thing to protect
 other services.

 All it has to do is confuse the receiver enough so that you can't
 trust its readings.

 Depends on the goal. For some strategies, blackout is the goal, for
 some
 getting the readings go haywire every once in a while suffice.

 Agreed!

 My 9V battery suggestion was for a localized blackout device.  You only
 have to make the receiver question each satellite's signal often enough
 for it to rule it out.  No way is CW necessary, or even desirable.

 As John suggested, someone (say the Chinese) could put these things in
 battery operated stuffed animals, and set them up to jam a little bit
 now and then.  After Xmas, the GPS landscape would be littered with
 these
 little stealth jammers, and willing supplicants to replace their
 batteries.

 -Chuck

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)


Hal Murray wrote:

cfhar...@erols.com said:

What makes you think it needs to be CW, and cannot be pulsed and
chirped?



All it has to do is confuse the receiver enough so that you can't
trust its readings. 


Why is pulse or chirp likely to be more confusing per W of jamming power?


I thought the GPS signal was spread spectrum so I wouldn't expect any simple 
pulse or chirp to be better at jamming than noise over the appropriate 
bandwidth.


If you know the spread spectrum details (which must be public or the receiver 
can't listen to the signal), then you might be able to mimic a satellite 
signal.  I think that needs the time, so you probably need to listen to the 
signal you are jamming.


Am I on the right track?  Is there a trick I'm missing?  (If so, how 
complicated is it?)


I think you are running into the jamming/spoofing definition of the 
problem. When you are jamming, you are transmitting a signal which just 
overshadows the propper signal but when you are spoofing you try to send 
a signal which looks like the propper signal.


A spoofing attack is a different story altogether. For a spoofer to 
confuse a receiver, it either needs to be there when the receiver turns 
on or the spoofer needs to transmitt signals having a position so near 
the receivers current signals that it can't discriminate them and then 
track onto the wrong signals.


The counter-measure towards spoofers is to used a keyed signal, in which 
case only delayed signal is available to the attacker, but for most 
cases the receiver should be able to handle that.


For jamming I think chirps or phase-noise transmitters is effective 
since they select no particular feature of the spreading code, but 
induces error into both the weak and strong features, which is then 
shifted by the expected doppler frequency. The sensitivity of jamming 
energy for various offsets from the carrier for a pseudo-random sequence 
can be retrieved by Fourier-transform (DFT).


Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)


J. Forster wrote:

Or even into MP3 players, iPods, laptops, or cell phones. Then they'd
wander all over the place too. With the latter two hosts, they could even
be controlled remotely and even be fairly powerful. Would you notice
having to recharge your battery a bit more often?


There is one report in which the laptops of ambulances had CPU 
frequencies in the neighborhood (1,5 GHz or 1,6 GHz if I recall 
correctly) of the GPS band and the GPS receiver lost tracking so they 
essentially lost functionality.


Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)


Francesco Ledda wrote:

Considering that the GPS antenna in aircrafts is mounted on top of fuselage,
and that its radiation pattern is upward, it seems that a ground jammer will
have an uphill battle.


Not all GPS receivers is sitting on flying airplanes. Far from it.

Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)


Mike,

A defective TV antenna preamp (oscillating in an uncontrolled manner),
on board a boat in California wiped out GPS for several kilometers!
Because it only wiped it out when the owner was watching TV, the
interferrence went on for months.  This is well documented.  Do a
google search and you will find the report from the guys that found
the jammer.

When a modern high sensitivity GPS receiver cannot get a fix through
the shingled roof of a house, you have to understand that the signals
are really weak.

The folks selling commercial GPS jammers are being rather brutish with their
methods.  They are using sledge hammers where a little tack hammer would
do nicely.

-Chuck

Mike Monett wrote:

Chuck Harris cfhar...@erols.com wrote:

What makes you think it needs to be CW, and cannot be pulsed and
chirped?

All it has to do is confuse the receiver enough so that you can't
trust its readings.

-Chuck


I said nothing about the type of modulation. The equipment I listed is
designed specifically to disrupt GPS. Presumably they use whatever
modulation method that gives the best results.

However, GPS is spread-spectrum, so it  inherently rejects noise that is
not correlated with the satellite signal. This means effective jamming
requires a lot more power than is available from a 9V transistor radio
battery, and even then, the range is only a few meters.


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

GPS receivers have considerable coding gain, which makes it possible for
them to detect such low signals in the first place. The jamming signal will
not benefit from the coding gain because it does not have the right coding
and will be uncorrelated to the actual spread-spectrum signals the receiver
is tracking.

This is probably 30 dB or more.

Also, you assume that your jammer has a similar antenna gain and radiation
efficiency as the GPS transmitter on the satellite, that is unlikely.

Bottom line, it is unlikely that a jammer running off a 9V battery, even on
a baloon will jam the entire US for weeks.

Can we go back to timing now? My 9V battery is running out...

Didier

 -Original Message-
 From: time-nuts-boun...@febo.com 
 [mailto:time-nuts-boun...@febo.com] On Behalf Of J. Forster
 Sent: Sunday, November 15, 2009 6:51 PM
 To: Discussion of precise time and frequency measurement
 Subject: Re: [time-nuts] The Demise of LORAN (was Re: 
 Reference oscillator accuracy)
 
 See my earlier post. Briefly:
 
 Antennas do not have an infinite front-to-back ratio. (40 dB)
 
 The path loss from a surface jammer to a plane (10 miles) is 
 many, many dB less than from plane to bird (15,000 miles).
 
 -John
 
 
 


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)


Magnus Danielson wrote:

Well, then you have to consider what the potential gain would be from 
such an attack. I fail to see the upside of that particular scenario. It 
would draw the attention over to them and in a field I think they rather 
stay calm about. Their ability to pull it off as such should not be 
doubted, but their resoning for it. Rather inefficient actually.


The Chinese seem to have a difficulty worrying about the ethics of some
of the things they do towards others.  Some simple examples would be the
lead in paints and plastics used in toys, melamine powder in milk, and pet
food, pork flavored cardboard in frozen dumplings, tainted raw ingredients
for heprin, the list goes on and on.

It may not be in the nation's political interests to jam our GPS signals
through toys, or other devices, but ... from what I have seen thus far,
you could easily find several dozen manufacturers in China that would be
willing to turn a blind eye to such a trojan payload in return for a few
bucks.

-Chuck Harris

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

Maybe, but what happens if the GPS in a large metropolitan area that is
overflown by a mix including General Aviation goes wonky? LA comes to mind
because there is a lot of north-south traffic directly over LAX.

-John

===

 The one the counts ARE! ;)

 -Original Message-
 From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
 Behalf Of Magnus Danielson
 Sent: Sunday, November 15, 2009 7:03 PM
 To: Discussion of precise time and frequency measurement
 Subject: Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator
 accuracy)

 Francesco Ledda wrote:
 Considering that the GPS antenna in aircrafts is mounted on top of
 fuselage,
 and that its radiation pattern is upward, it seems that a ground jammer
 will
 have an uphill battle.

 Not all GPS receivers is sitting on flying airplanes. Far from it.

 Cheers,
 Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

Not all GPSs are on airplanes, but those I am really worried about are.

I don't care if the GPS receiver in my cell phone stops working in some
locations, it does not work everywhere to begin with (like in the house, I
can't use it to find the bathroom in the dark...), but I worry that the one
guiding a missile or a fighter plane might not work. I also worry that the
one abord a large passenger aircraft might not work. Most of those that are
stationary or move on the ground or on water, I am not too worried about.

For instance, the local garbage pickup people use GPS to locate the houses
of customers who have unusual (large or unsafe, or possibly contaminating)
garbage to pickup. I have had a dead TV on the side of my house for 3 weeks,
three times I called and 3 times they missed it because the GPS guided them
to my front door (my normal mailing address), but I live on a corner lot and
the garbage pickup is on the side of the house, by the garage. If that
particular GPS receiver stopped working and forced the employees to look
around, it would not bother me (the TV ended up in the trash can. After 3
times and 3 weeks, I assumed I had done a reasonable attempt at avoiding
putting too much lead in the garbage, and it had to go.)

Didier 

 -Original Message-
 From: time-nuts-boun...@febo.com 
 [mailto:time-nuts-boun...@febo.com] On Behalf Of Magnus Danielson
 Sent: Sunday, November 15, 2009 7:03 PM
 To: Discussion of precise time and frequency measurement
 Subject: Re: [time-nuts] The Demise of LORAN (was Re: 
 Reference oscillator accuracy)
 
 Francesco Ledda wrote:
  Considering that the GPS antenna in aircrafts is mounted on top of 
  fuselage, and that its radiation pattern is upward, it seems that a 
  ground jammer will have an uphill battle.
 
 Not all GPS receivers is sitting on flying airplanes. Far from it.
 
 Cheers,
 Magnus
 
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 go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

2009-11-15 Thread Bruce Rahn


Hal Murray wrote:

cfhar...@erols.com said:
  

What makes you think it needs to be CW, and cannot be pulsed and
chirped?



  

All it has to do is confuse the receiver enough so that you can't
trust its readings. 



Why is pulse or chirp likely to be more confusing per W of jamming power?


Perhaps this reference will answer some of the questions present here:

http://www.navcomtech.com/Support/Download/Sapphire%20Jamming%20Test%20Report%208%20Jan%202007v3.pdf

One factor I have not seen anyone address is the effectiveness of 
jamming as a function of the receiver state.  A GPS receiver will be 
much more susceptible to jamming when it is trying to acquire and lock 
onto a satellite signal than it is after lock and tracking has been 
achieved. 


Bruce, WB9ANQ

--
Bruce Rahn

Wisdom has two parts:
1.  having a lot to say; and
2.  not saying it!



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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

The one the counts ARE! ;)

-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Magnus Danielson
Sent: Sunday, November 15, 2009 7:03 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator
accuracy)

Francesco Ledda wrote:
 Considering that the GPS antenna in aircrafts is mounted on top of
fuselage,
 and that its radiation pattern is upward, it seems that a ground jammer
will
 have an uphill battle.

Not all GPS receivers is sitting on flying airplanes. Far from it.

Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

2009-11-15 Thread Justin Pinnix

Contrary to popular belief, us pilots do know how to fly without GPS.  I
have never seen an IFR aircraft with a GPS that didn't also have a VOR
receiver.  Any VFR aircraft can be navigated using the Mk I eyeball.

IFR certified GPSes have integrity monitoring.  So, if the signal gets
jammed or there is another system failure, the approach should be aborted
and the flight switched to another navigation means.

This LORAN debate is all well and good, but most of the general aviation
fleet does not have LORAN receivers.  They haven't been manufactured in
years.

On Sun, Nov 15, 2009 at 8:33 PM, Didier Juges did...@cox.net wrote:

 Not all GPSs are on airplanes, but those I am really worried about are.

 I don't care if the GPS receiver in my cell phone stops working in some
 locations, it does not work everywhere to begin with (like in the house, I
 can't use it to find the bathroom in the dark...), but I worry that the one
 guiding a missile or a fighter plane might not work. I also worry that the
 one abord a large passenger aircraft might not work. Most of those that are
 stationary or move on the ground or on water, I am not too worried about.

 For instance, the local garbage pickup people use GPS to locate the houses
 of customers who have unusual (large or unsafe, or possibly contaminating)
 garbage to pickup. I have had a dead TV on the side of my house for 3
 weeks,
 three times I called and 3 times they missed it because the GPS guided them
 to my front door (my normal mailing address), but I live on a corner lot
 and
 the garbage pickup is on the side of the house, by the garage. If that
 particular GPS receiver stopped working and forced the employees to look
 around, it would not bother me (the TV ended up in the trash can. After 3
 times and 3 weeks, I assumed I had done a reasonable attempt at avoiding
 putting too much lead in the garbage, and it had to go.)

 Didier

  -Original Message-
  From: time-nuts-boun...@febo.com
  [mailto:time-nuts-boun...@febo.com] On Behalf Of Magnus Danielson
  Sent: Sunday, November 15, 2009 7:03 PM
  To: Discussion of precise time and frequency measurement
  Subject: Re: [time-nuts] The Demise of LORAN (was Re:
  Reference oscillator accuracy)
 
  Francesco Ledda wrote:
   Considering that the GPS antenna in aircrafts is mounted on top of
   fuselage, and that its radiation pattern is upward, it seems that a
   ground jammer will have an uphill battle.
 
  Not all GPS receivers is sitting on flying airplanes. Far from it.
 
  Cheers,
  Magnus
 
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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)


Mike,

Mike Monett wrote:

I said nothing about the type of modulation. The equipment I listed is
designed specifically to disrupt GPS. Presumably they use whatever
modulation method that gives the best results.

However, GPS is spread-spectrum, so it  inherently rejects noise that is
not correlated with the satellite signal. This means effective jamming
requires a lot more power than is available from a 9V transistor radio
battery, and even then, the range is only a few meters.


The power of de-correlation is related to the length of the 
pseudo-random sequence. This relates back to the codes auto-correlation 
shape.


The C/A code has a length of 1023 chips, giving a correlation gain of 
about 30 dB.


The P code has a length of 7*86400*10,23E6 chips (a GPS week) but only 
fraction of that can be used for de-correlation.


Looking at the detailed codes, the vunerability of C/A codes is worse, 
for PRN 1 the suppression is only -22,71 dB at 42 kHz sideband.


But these coding gains comes to no use if the input is saturated for 
most of the times. Simple AGC strategies would allow the AGC to be 
captured by the CW signal for instance. Lack of filtering would allow 
out-of-bandwidth signals to infect the input etc. etc.


Pre-digitalization code de-correlation is less sensitive to jamming, but 
comes at the price of 3 times number of channels analog decorrelators 
and integrators. Then again, it only solves part of the problem.


The tracking threshold of the particular receiver in its environment has 
a huge effect. Support systems such as clock, movement sensors etc. can 
allow for tighter loop filters and thus allow the channels having a 
lower threshold and that would aid in the jamming resistance too.


Regardless, the code-lengths isn't a particular good measure on the 
resistance to jamming. The P(Y) code is only about 10 dB better than C/A 
code in that respect, and M code gives another dB or so.


Cheers,
Magnus

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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

The commercial jammers referred to in an earlier post advertise 10 to 45m or
so range, with significant power levels and battery life measured in a few
hours. Considering that these devices are illegal to begin with, I have to
assume that these figures are probably optimistic (optimistic advertisement
is probably the least of their concern.)

If I were a pilot, I would probably be more worried about the kid playing
with his Nintendo in 15A (or his father trying to retrieve his email with
his GSM smart phone) during approach than a jammer on the ground.

Didier

 -Original Message-
 From: time-nuts-boun...@febo.com 
 [mailto:time-nuts-boun...@febo.com] On Behalf Of J. Forster
 Sent: Sunday, November 15, 2009 6:38 PM
 To: Discussion of precise time and frequency measurement
 Subject: Re: [time-nuts] The Demise of LORAN (was Re: 
 Reference oscillator accuracy)
 
 Even 10 KM is pretty useful. If the thing were solar powered 
 with a supercap battery it could easly transmit for say 2 
 minutes per hour w/ significant power. It'd be hard to find 
 if the on times were generated by a multiple fedback CMOS 
 shift register.
 
 -John
 


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

2009-11-15 Thread Bruce Griffiths


Didier

As jammers those devices are extremely inefficient.
They may well rely on the inefficient generation and radiation of a very 
high order harmonic of the clock of an unshielded legal device.


A commercial GPS receiver may require a signal as small as 60dB (depends 
on the operating mode, and receiver design) above the GPS signal at the 
receiver input.

An ERP of a few microwatts should suffice to achieve the claimed range.

Bruce

Didier Juges wrote:

The commercial jammers referred to in an earlier post advertise 10 to 45m or
so range, with significant power levels and battery life measured in a few
hours. Considering that these devices are illegal to begin with, I have to
assume that these figures are probably optimistic (optimistic advertisement
is probably the least of their concern.)

If I were a pilot, I would probably be more worried about the kid playing
with his Nintendo in 15A (or his father trying to retrieve his email with
his GSM smart phone) during approach than a jammer on the ground.

Didier

   

-Original Message-
From: time-nuts-boun...@febo.com
[mailto:time-nuts-boun...@febo.com] On Behalf Of J. Forster
Sent: Sunday, November 15, 2009 6:38 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] The Demise of LORAN (was Re:
Reference oscillator accuracy)

Even 10 KM is pretty useful. If the thing were solar powered
with a supercap battery it could easly transmit for say 2
minutes per hour w/ significant power. It'd be hard to find
if the on times were generated by a multiple fedback CMOS
shift register.

-John

 


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

I think the problem with the Monterey Bay jammer was that he was jamming the
DGPS correction signal, not the GPS signal itself. The DGPS correction
signal is sent over the UHF band. Most marine GPS are DGPS because they need
the better resolution it provides, particularly to find buoys and channel
markers in the fog. The DGPS correction signal does not benefit from the
spread-spectrum modulation and associated jamming resistance of the GPS
signal itself.

Didier

 -Original Message-
 From: time-nuts-boun...@febo.com 
 [mailto:time-nuts-boun...@febo.com] On Behalf Of Hal Murray
 Sent: Sunday, November 15, 2009 6:30 PM
 To: Discussion of precise time and frequency measurement
 Subject: Re: [time-nuts] The Demise of LORAN (was Re: 
 Reference oscillator accuracy)
 
   Jamming Range : Average 40 meters radius  Output Power  : 
 Total 6.5 
  Watt
 
   ratio : 40/6.5 = 6.15 meters/watt
 
 Isn't received power 1/R-squared?
 
 I think those calculations should be radius-squared/watts
 
 
 I find it interesting that the products designed as jammers 
 have ranges of only a few 10s of meters while a recent 
 message here said 1/2 mile from a digital-radio link that was 
 transmitting on 315 MHz.  (aka designed for something else 
 rather than as a jammer)
 
 Similarly, the Monterey Bay jammer wasn't trying to be a 
 jammer, and it wiped out a huge area.
 


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

2009-11-15 Thread David I. Emery

On Sun, Nov 15, 2009 at 08:22:50PM -0600, Didier Juges wrote:
 I think the problem with the Monterey Bay jammer was that he was jamming the
 DGPS correction signal, not the GPS signal itself. The DGPS correction
 signal is sent over the UHF band. Most marine GPS are DGPS because they need
 the better resolution it provides, particularly to find buoys and channel
 markers in the fog. The DGPS correction signal does not benefit from the
 spread-spectrum modulation and associated jamming resistance of the GPS
 signal itself.

That is the first I've heard of a UHF DGPS correction transmission
can you provide a frequency and modulation mode ?Most I know of are
re purposed LF NDBs or similar transmitters in the 200 to 400 KHz or
so range that transmit a PSK'd carrier with the DGPS data at fairly low
speed on it.

I have heard of cases of wide area GPS outages noted by many
folks with NON DGPS receivers (DGPS receivers  mostly will just indicate
no DGPS available and still show a pretty good position) that were
caused by UHF signals on the L2 frequency... though I am sure there are
incidents of accidental interference to LF or other distribution of
DGPS.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either.


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)

I was shooting from the hip, I thought the DGPS signals were sent at UHF,
but maybe not, but that's not the point. The point is that you can
significantly affect DGPS operation without having to jam the GPS signal
itself. 

I found a reference saying the Monterey Bay jammer was jamming the DGPS
station, rather than the DGPS signal. I have not found the original article
I was looking for about it, but I think I remember that the boaters and
Coast Guards were the most affected, as you should expect because they rely
on and need the additional accuracy of the DGPS system.

Didier

 -Original Message-
 From: time-nuts-boun...@febo.com 
 [mailto:time-nuts-boun...@febo.com] On Behalf Of David I. Emery
 Sent: Sunday, November 15, 2009 8:30 PM
 To: Discussion of precise time and frequency measurement
 Subject: Re: [time-nuts] The Demise of LORAN (was Re: 
 Reference oscillatoraccuracy)
 
 
   That is the first I've heard of a UHF DGPS correction 
 transmission
 can you provide a frequency and modulation mode ?Most I 
 know of are
 re purposed LF NDBs or similar transmitters in the 200 to 400 
 KHz or so range that transmit a PSK'd carrier with the DGPS 
 data at fairly low speed on it.
 
   I have heard of cases of wide area GPS outages noted by 
 many folks with NON DGPS receivers (DGPS receivers  mostly 
 will just indicate no DGPS available and still show a pretty 
 good position) that were caused by UHF signals on the L2 
 frequency... though I am sure there are incidents of 
 accidental interference to LF or other distribution of DGPS.
 


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

Bruce,

I agree with your calculation and conclusion, as far as commercial consumer
GPS receivers are concerned.

A data sheet that was linked in a previous post for an aviation-grade
commercial GPS receiver indicated resistance to signals -30dBm at the
receiver input. That is quite considerable, and much better than the
hand-held consumer units (by 30dB?)

I would expect planes and other potential high value targets to have
receivers of similar performance.

I don't disagree that it would be fairly easy to disrupt the consumer
devices, but other than a few missed appointments and frustrated gadget
freaks, and the occasional emergency vehicle not finding its way to the
scene of an accident, that would be more of a problem) I am not too worried
about the consequences of that.

The thread started with the loss of the LORAN system, and nobody (maybe I am
going out on a limb here) ever used a LORAN receiver in his car to find the
nearest restaurant :)

I think the people who should complain the most about the loss of LORAN are
the boaters, but they are the one who embrassed GPS the first and are it's
biggest advocates!!! I know, I live on the coast of Florida.

Didier

 -Original Message-
 From: time-nuts-boun...@febo.com 
 [mailto:time-nuts-boun...@febo.com] On Behalf Of Bruce Griffiths
 Sent: Sunday, November 15, 2009 8:21 PM
 To: Discussion of precise time and frequency measurement
 Subject: Re: [time-nuts] The Demise of LORAN (was Re: 
 Reference oscillator accuracy)
 
 Didier
 
 As jammers those devices are extremely inefficient.
 They may well rely on the inefficient generation and 
 radiation of a very high order harmonic of the clock of an 
 unshielded legal device.
 
 A commercial GPS receiver may require a signal as small as 
 60dB (depends on the operating mode, and receiver design) 
 above the GPS signal at the receiver input.
 An ERP of a few microwatts should suffice to achieve the 
 claimed range.
 
 Bruce
 
 Didier Juges wrote:
  The commercial jammers referred to in an earlier post 
 advertise 10 to 
  45m or so range, with significant power levels and battery life 
  measured in a few hours. Considering that these devices are 
 illegal to 
  begin with, I have to assume that these figures are probably 
  optimistic (optimistic advertisement is probably the least of their 
  concern.)
 
  If I were a pilot, I would probably be more worried about the kid 
  playing with his Nintendo in 15A (or his father trying to 
 retrieve his 
  email with his GSM smart phone) during approach than a 
 jammer on the ground.
 
  Didier
 
 
  -Original Message-
  From: time-nuts-boun...@febo.com
  [mailto:time-nuts-boun...@febo.com] On Behalf Of J. Forster
  Sent: Sunday, November 15, 2009 6:38 PM
  To: Discussion of precise time and frequency measurement
  Subject: Re: [time-nuts] The Demise of LORAN (was Re:
  Reference oscillator accuracy)
 
  Even 10 KM is pretty useful. If the thing were solar 
 powered with a 
  supercap battery it could easly transmit for say 2 
 minutes per hour 
  w/ significant power. It'd be hard to find if the on times were 
  generated by a multiple fedback CMOS shift register.
 
  -John
 
   
 
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Re: [time-nuts] The Demise of LORAN (was Re: Referenceoscillatoraccuracy)

2009-11-15 Thread jmfranke


For the marina story, see:
http://www.gpsworld.com/gps/system-challenge/the-hunt-rfi-776

The L1 signal was unintentionally jammed.

John  WA4WDL

--
From: Didier Juges did...@cox.net
Sent: Sunday, November 15, 2009 9:55 PM
To: 'Discussion of precise time and frequency measurement' 
time-nuts@febo.com
Subject: Re: [time-nuts] The Demise of LORAN (was Re: 
Referenceoscillatoraccuracy)



I was shooting from the hip, I thought the DGPS signals were sent at UHF,
but maybe not, but that's not the point. The point is that you can
significantly affect DGPS operation without having to jam the GPS signal
itself.

I found a reference saying the Monterey Bay jammer was jamming the DGPS
station, rather than the DGPS signal. I have not found the original 
article

I was looking for about it, but I think I remember that the boaters and
Coast Guards were the most affected, as you should expect because they 
rely

on and need the additional accuracy of the DGPS system.

Didier


-Original Message-
From: time-nuts-boun...@febo.com
[mailto:time-nuts-boun...@febo.com] On Behalf Of David I. Emery
Sent: Sunday, November 15, 2009 8:30 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] The Demise of LORAN (was Re:
Reference oscillatoraccuracy)


That is the first I've heard of a UHF DGPS correction
transmission
can you provide a frequency and modulation mode ?Most I
know of are
re purposed LF NDBs or similar transmitters in the 200 to 400
KHz or so range that transmit a PSK'd carrier with the DGPS
data at fairly low speed on it.

I have heard of cases of wide area GPS outages noted by
many folks with NON DGPS receivers (DGPS receivers  mostly
will just indicate no DGPS available and still show a pretty
good position) that were caused by UHF signals on the L2
frequency... though I am sure there are incidents of
accidental interference to LF or other distribution of DGPS.




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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

My first contact with LORAN was at the bankrupcy of a local company that
supplied tracking and location services for trucking companies. The trucks
had a receiver that sent data back to home base via two-way radio and home
pbase computed positions. I was only nteresteed in buying their mimis.

In the early 80s I was playing around with uP (8085) based LORAN receivers
(Made by Appelco/Raytheon). One version read out time differences and a
more advanced (w/ 2x 8085s) version read out Lat  Long directly. Either
would pinpoint my location to 100' class. It was accurate navigation in a
two-way radio sized box.

There were, of course, no map or chart displays. Imagine what 20+ years of
development would have brought.

-John

=


 Bruce,

 I agree with your calculation and conclusion, as far as commercial
 consumer
 GPS receivers are concerned.

 A data sheet that was linked in a previous post for an aviation-grade
 commercial GPS receiver indicated resistance to signals -30dBm at the
 receiver input. That is quite considerable, and much better than the
 hand-held consumer units (by 30dB?)

 I would expect planes and other potential high value targets to have
 receivers of similar performance.

 I don't disagree that it would be fairly easy to disrupt the consumer
 devices, but other than a few missed appointments and frustrated gadget
 freaks, and the occasional emergency vehicle not finding its way to the
 scene of an accident, that would be more of a problem) I am not too
 worried
 about the consequences of that.

 The thread started with the loss of the LORAN system, and nobody (maybe I
 am
 going out on a limb here) ever used a LORAN receiver in his car to find
 the
 nearest restaurant :)

 I think the people who should complain the most about the loss of LORAN
 are
 the boaters, but they are the one who embrassed GPS the first and are it's
 biggest advocates!!! I know, I live on the coast of Florida.

 Didier



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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)

2009-11-15 Thread Bill Hawkins

Ahh, must jump into feeding frenzy . . .

Here we find the limitations of the 3 pound (1.5 kilogram) human brain.

One must become a specialist to become informed on a particular field,
because the scope of that field increases exponentially with time (the
subject of this group).

Not everyone keeps up, and not everyone who looks at the bleeding edge
thinks that past experience and knowledge has been included. And so we enter
an alternative universe similar to the discussion of politics or religion.
Think about why all of these diverse opinions exist.

The brain can't comprehend something for which it has no comprehending
structures of nerves. We stopped having enough structures sometime in the
16th century. We forge into the future only because we specialize into areas
that do fit the brain, but no two people have the same brain structures.

And so, dear friends, we are descending not into Alice's rabbit hole, but a
rat hole with an infinite number of twisty little passages, all somewhat
alike. The decision was made, some time ago. The time for discussion has
passed. Please return the list to its subject matter.

YMMV

Bill Hawkins


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

2009-11-15 Thread David I. Emery

On Sun, Nov 15, 2009 at 08:56:36PM -0600, Didier Juges wrote:
 
 I don't disagree that it would be fairly easy to disrupt the consumer
 devices, but other than a few missed appointments and frustrated gadget
 freaks, and the occasional emergency vehicle not finding its way to the
 scene of an accident, that would be more of a problem) I am not too worried
 about the consequences of that.

GPS has been widely used for time and frequency sync in radio
systems of various sorts - some depend on it for successful simulcast
from multiple transmitters (including many public safety radio systems)
and while there is SUPPOSED to be significant holdover, there is are
always those situations where nobody has EVER checked that it works...
And what will holdover do about LONG TERM outages of GPS ?   Perhaps 
folks are willing to bet the whole infrastructure on the supposition that
we could NEVER see a complete long term loss of signal (using civilian
receivers with modest anti jam abilities) in a particular location or
region - I am not exactly sure what alternative might exist though I
guess there are some for time and frequency - terrestrial GPS beacons
from high points that could lock up a cell system in a region come to
mind...

And more and more and more stuff depends on more or less
ignorant and sometimes not very bright operators expecting that the GPS
positions are always there or they don't know what to do.   And if GPS
is almost always reliably there there may well be little or no practical
training about what to do if it fails.   Failure modes and paths in code
and procedures (and sometimes even actual hardware) which aren't often
tested or exercised usually fail when actually needed and often in
entirely unanticipated ways - maybe the backup ALSO depends on GPS in
some way the system designers never thought about (or knew could
happen)...

LORAN C represents a viable (albeit not often deployed) backup
to time and frequency control and could be implemented in modern
hardware as a backup location service at reasonably low cost for those
applications where that is important enough.

 
 The thread started with the loss of the LORAN system, and nobody (maybe I am
 going out on a limb here) ever used a LORAN receiver in his car to find the
 nearest restaurant :)

Actually readers of this list have, though not in recent times I guess.
 
 I think the people who should complain the most about the loss of LORAN are
 the boaters, but they are the one who embrassed GPS the first and are it's
 biggest advocates!!! I know, I live on the coast of Florida.

An enhanced LORAN that has some of the accuracy and automation
of a GPS receiver exists... I suspect boaters care most about
convenience (and accuracy) and found GPS easier.   Certainly so compared
to earlier LORAN C gear.

And of course there is another issue with GPS, it is controlled
by the DOD and is supposed to have the ability to deny service in a
region if conditions are sufficiently apocalyptic to require it.   For
folks worried about this (more outside than inside the US obviously)
LORAN is a local resource they may control and certainly can if they
make a more or less modest investment in the ability to do so.   Some
(large) players are of course planning their own space based systems for
just this reason but LORAN can be implemented by most nation states...

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either.


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

2009-11-15 Thread David I. Emery

On Sun, Nov 15, 2009 at 07:17:37PM -0800, J. Forster wrote:

 There were, of course, no map or chart displays. Imagine what 20+ years of
 development would have brought.

E Loran could supply the same basic position information as input
to charting and mapping software as GPS does... most of the code doesn't
care where the position came from one wit

But I am sure you know that (we are in violant agreement).


 -John
 

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either.


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Re: [time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)