[time-nuts] Lucent RFTG-m-XO ...

geo geo at drbertges.de
Mon Apr 2 16:13:11 EDT 2007


Hi Jason,

perhaps i am the only "german", currently available. My english is not good
but i hope, it's less pain for you to read my "english" than to read the
german text ;-)

Best regards

Martin Bertges



Description of Lucent RFTG-m-XO GPS frequency standard
ver. 20.03.2007

Introduction
The Lucent frequency and timing modules (modul number RF(T)g-m) had been used
in GPS basestations for synchronization; there are various models available
(quartz / rubidium or GPS based), made from 1998 to 2000; no official manuals
or descriptions are available but the parts are described in newsgroups and
amateurs like "time-nuts" have collected a lot of information (which is
available in emails only, with a low "signal-to-noise ratio"); 

i have analysed and expanded this information, based on own observations;
I will describe the RFTG-m-XO in details: it is a so called "GPS disciplined
frequency standard" or GPSDO; that means the local OCXO is "disciplined"
by the GPS based 1PPS signal on using a microcontroller; the OCXO parameters
(like temperature drift and aging) are determined and the control voltage
of the OCXO is calculated and applied; a "holdover status" is possible,
when sufficient GPS signals are not available; so the resulting accuracy of
the 1PPS/15MHz signal is much higher than based on a single quartz oscillator;
the GPS receiver is a well documented Motorola VP Oncore;
the GPS receiver's serial data (position, time and status) are internally
as TTL signals available and can be used with TAC32 or other programs; 

output:
via the serial interface (J6) time and status are transmitted once per second;

(the text following should be read from the JPEG file ;-) )

Character 1-4 are unimportant, 5-6 are status, 12-19 shows GPS second (in hex 
format since 6.Jan.1980), 20-23 version number, 24-25 checksum;

(the descriptions of the LEDs, J4/J6/J5/J3/J7/J2 and P1 are in english ;-) )

Connector J6 holds 1PPS output with a standard deviation of about 30ns compared 
to UTC; can be used for clock comparison or NTP server synchronisation; 
J6 pin1/2 holds a RS485 signal for longer transmission lines;

there is also a sine signal available with a SMA connector (15MHz); this signal
is based on the GPS controlled 10MHz DCXO (?); the latter can be identified
easyly (should be buffered, when used for own purposes) frequency accuracy
is about +-E-10 (tracking);

Operation is easy; after connecting 24V DC on P1 and a GPS antenna on J7,
the ON-LED show green light after about 15 minutes, indicating enough 
satellites; the output signals are valid then; to get a good "holdover"
performance a longer operation period is neccessary;

Sources:
time-nuts-mailing list http://www.febo.com/pipermail/time-nuts/
Motorola Oncore http://www.corallinks/tmbroker/images/oncore_eng_notes.pdf








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