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

Didier Juges didier at cox.net
Mon Nov 16 02:56:36 UTC 2009


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-bounces at febo.com 
> [mailto:time-nuts-bounces at 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-bounces at febo.com
> >> [mailto:time-nuts-bounces at 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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> >    
> 
> 
> 
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