[time-nuts] Lucent RFG-M-RG and XO

Richard H McCorkle mccorkle at ptialaska.net
Thu Dec 28 14:44:00 EST 2006


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" <jra at febo.com>
To: "Discussion of precise time and frequency measurement"
<time-nuts at 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.
>
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