anyone running GPS clocks in Southeastern Georgia?
cb.list6 at gmail.com
Sun Jan 23 10:32:52 CST 2011
On Jan 21, 2011 6:49 PM, "Pete Carah" <pete at altadena.net> wrote:
> On 01/21/2011 04:29 PM, Lamar Owen wrote:
> > On Friday, January 21, 2011 04:23:52 pm Michael Holstein wrote:
> >> Aren't CDMA BTS clocked off GPS?
> > Yep; and many of the aftermarket GPS receivers commonly used for the
disciplined clock for NTP originally came from that service (Agilent/HP
Z3801 and Z3816, for instance).
> Boo. You can't find the 3816 much anymore and the 3801 isn't as good
> (fine for most ntp purposes,though) (the difference is mostly in
> internal measurement software and how long it will hold without the gps
> And Symmetricom bought that line from HP, still sells one comparable to
> the Z3801 but not like the 3816 for a decent price. Personally I'd
> build one up out of an LPRO, a Trimble timing receiver (current
> replacement for the Oncore used in the
> Z38xx units, last I checked it was under $100), a MSP430 (probably a
> fairly high-end one to get enough program space for a good PLL) and some
> external logic for phase comparators (I don't know if the timer capture
> modes in the 430 are good enough by themselves...) The most expensive
> single part would be a decent timing antenna (yes, timing antennas *are*
> different from the usual civilian positioning antennas; there is a
> reason why the base is larger diameter than the rest...)
> Actually, does anyone still do soft handoff with UMTS? That was much of
Yes. Providing accurate clock to a cell site is critical for 2/3/4g. This
usually requires a primary (GPS) and backup (1588).
> the reason why old CDMA needed a GPS reference.
> -- Pete
More information about the NANOG