On Jan 21, 2011 6:49 PM, "Pete Carah" <p...@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 > signal). > 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). Cb > the reason why old CDMA needed a GPS reference. > > -- Pete > >
