Back when these Lucent units were first appearing GPS had not yet been implemented at the cell sites here in Alaska. The rubidium was too noisy for direct frequency synthesis, so the XO unit was phase locked to the rubidium to provide the long-term stability needed, and the XO output was up-converted for the system clock. By using the XO to smooth the rubidium output the phase noise in the system clock was reduced due to better short-term stability in the XO. As I remember it (It's been a while) the 10M Rb disciplined the 10M XO, which was divided by 2, multiplied by 3, filtered, and supplied as the 15M system clock. The XO was always supplying the 15M system clock, and "standby" just meant the XO was locked to the rubidium, which was acting as the primary frequency reference. When the rubidium failed the system alarm output went high, XO PLL went into hold, the standby light on the XO extinguished, and the undisciplined XO became the source until the rubidium could be replaced. The GPS connection didn't appear until later units and disciplined the XO during normal operation, with failover on extended GPS loss to disciplining the XO from the rubidium. Hope this helps in figuring out the why of the system connections.
Have Fun! Richard ----- Original Message ----- From: "John Ackermann N8UR" <[EMAIL PROTECTED]> To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Sent: Thursday, December 28, 2006 4:51 AM Subject: Re: [time-nuts] Lucent RFG-M-RG and XO > Thanks for the information, Gerald. > > Could the fault light without 10MHz input be as simple as the system > reporting failure of the Rb? i.e., the XO unit working OK, but just > reporting that the system wasn't operating properly. > > Like you, I'm having trouble sussing out just why this thing is designed > as it is, which oscillator is primary, and why... > > John > ---- > > Gerald Molenkamp said the following on 12/28/2006 06:27 AM: > > Some 5 years ago I recovered one of each, ( RFG-M-RG & RFG-M-XO ) from a Lucent CDMA BSC site here in Australia. Both units were only 12 months old, at that stage inter-connected via the J5 "interface" 10MHz out to 10MHz in from the RG to XO respectively and of course 24 VDC. > > > > After some reverse engineering of the BSC, I never understood the reason for the REG-M-XO in the BSC as it required a 10 MHz input from the RG for it to operate properly, e.g. the fault LED off. The 15 MHz signal is the synthesiser reference output that is fed into the BSC radio, synchronisation then propagates through the CDMA network, which I assume is used as one of many Primary Reference clocks ( PRC ) for the network of many BSC's. My assumption is that the XO is used as a back-up PRC in the event of RG failure, or as part of the hold-over system, but this was questionable. > > _______________________________________________ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
