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

Magnus Danielson magnus at rubidium.dyndns.org
Sun Nov 15 17:55:16 UTC 2009


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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