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

Magnus Danielson magnus at rubidium.dyndns.org
Mon Nov 16 00:39:42 UTC 2009


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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