[time-nuts] GPS backup for the stationary time and frequencyuser

Magnus Danielson magnus at rubidium.dyndns.org
Sat Oct 9 20:43:24 UTC 2010


On 10/09/2010 09:47 PM, jimlux wrote:
> Bob Camp wrote:
>> Hi
>>
>> The Russians have been willing to sell GPS jammers for quite a while.
>> They aren't terribly expensive. Their export controls are a bit
>> different than the US's.
>>
>> Bob
>>
>
> Simple GPS jammers are pretty easy, since consumer GPS is very
> vulnerable to repeater jammers. Hmm I wonder if that would adversely
> affect a GPSDO? Probably not, since the repeated signal is just as
> stable as the original one.

Well, a real jammer will just prohibit the reception of signal while a 
spoofing attempt would provide a false signal. There is no reason to 
assume that a spoofed signal would be stable. Also, the spoofing attempt 
we talked about through the WAAS bent-pipe does not necessarily make the 
GPS receiver lock onto all the spoofed signals, but a shifting selection 
of correct and spoofed signals. RAIM in receivers would help to some 
degree, If it fully locks on to the spoofing signal, just to be thrown 
away in time and that should upset most GPSDOs quite a bit.

> jammers probably aren't subject to export controls, just local usage
> regulations (e.g. illegal in US because of FCC rules prohibiting them).
>
> the ITAR (which is the big deal in the export controls world, compared
> to EAR) is the *International* Tariff, so everyone is a signatory, and
> we're all in the same boat as to what is a munition and what is not.
> Granted, enforcement and interpretation varies.

Someone seriously wanting to use one for some reason would not care 
significantly and found ways around it. Someone with sufficient 
knowledge would build one if needing to.

Cheers,
Magnus




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