[ntp:questions] Questions about joining pool.ntp.org
David J Taylor
david-taylor at blueyonder.co.uk.invalid
Sun Aug 28 21:22:42 UTC 2011
"Brian Utterback" <brian.utterback at oracle.com> wrote in message
news:4E5AA449.3090707 at oracle.com...
> There are two sides with different figures. The GPS industry says that
> 500,000,000 units would be affected. The company LightSquared says it is
> really 200,000. The DOD standards for GPS receivers issued in 2008 says
> that devices should require no more than a 4 MHz gap between bands, and
> LightSquared is allowing a 23 Mhz gap, but GPS manufacturers say that
> they need a 34 Mhz gap. Further, the DOD warned GPS manufacturers in
> 2000 that they were not sufficiently selective.
> Ouch. The GPS manufacturers took short cuts, and just like the Netgear
> fiasco, there are millions of units that will be affected with no way to
> fix them. And it is the users that are going to get hit.
> Interestingly, the FCC has said to both LightSquared and the GPS
> industry to cut the BS and come up with the real figures.
While not identical, we have experience in the UK of high-power pager
transmitters being placed adjacent to a 136-138 MHz satellite band. In
practice, it is near impossible to filter out the pager transmissions so
if you live near a pager transmitter, satellite reception is completely
ruined. It didn't help that some pagers were actually placed /inside/ an
internationally protected frequency band.
Anyone with experience of RF design will soon tell you that at 1.5 GHz a 4
MHz separation is completely unrealistic, and 23 MHz is very tight.
Something nearer 50 MHz is getting realistic. Don't forget the sideband
energy from these digital transmissions, and the below zero
signal-to-noise ratio of GPS.
I do hope there is a satisfactory resolution.
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