On Jan 21, 2011 6:49 PM, "Pete Carah" <pete@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