[time-nuts] New pics of RFTG-m-Rb, and some comparison details

Jim Miller timenuts at jcmco.com
Sat Dec 30 15:33:57 EST 2006


On Dec 30, 2006, at 2:24 PM, John Ackermann N8UR wrote:

> My RFTG-m-Rb arrived yesterday, so of course it's in pieces on the  
> bench
> today.  Photos (along with those of the -XO) are at
> http://www.febo.com/time-freq/hardware/Lucent_GPSDO/

I did some reverse engineering on my RFTG-m-RB last night.  The  
information below is what I've found so far.

Upon power-up the unit will sit for a while, sometimes 10 minutes or  
more, presumably allowing the
Rb to lock and settle.  During this time there is a 10MHz square wave  
output from "TP" but no output from the "10 MHz REF" nor the 15 MHz  
connector.   The FAULT and NOGPS lights are illuminated.

After the warmup period the FAULT light extinguishes, the ON light  
illuminates, and the 10 and 15 MHz connectors become active.  The  
10MHz REF OUT is squarewave, the 15 MHz is sine.

Note that this behavior is fundamentally identical to the older  
stainless box units containing three boards and an FRS-C  that have  
made their way around Ebay for a year or two.  Could the RFTG have  
been the replacement for the stainless box units?

Connectors
----------------

J5 INTERFACE:

J5-1:	Comes high (+5) after the warmup period is complete and the  
reference outputs are enabled.

J5-2:	Unknown, maybe N/C

J5-3:	Unknown but appears connected to something. GPS IN?

J5-4:	GPS TX DATA (GPS header, pad 8)

J5-5:	Unknown but appears connected to something. GPS IN?

J5-6:	Unknown, maybe N/C

J5-7:	PPS output from internal source (not GPS)

J5-8:	Unknown, maybe N/C

J5-9:	GPS PPS OUT (GPS header, pad 6)

Stimuli to GPS pin 8 (TX DATA) appears on J5-4.

Stimuli to GPS pin 6 (PPS OUT) appears on J5-9.

Since GPS TX and PPS show up on J5, I am betting that GPS RX is also  
available on this connector. See below.

------------

RS-485/1PPS connector:

J6-1:	diff. output - 1 PPS+ from internal source

J6-2:	?

J6-3:	?

J6-4:	? believed to be diff. serial RXD input.

J6-5:	diff. output - TXD serial -

J6-6:	diff. output - 1 PPS- from internal source

J6-7:	?

J6-8:	? believed to be diff serial RXD input

J6-9:	diff output - TXD serial +

Data on J6 TXD+/- is 9600 8N1 and is of the form:

:000000010100000000E004E6

These updates come once per second and a couple of the nybbles change  
when it moves from warmup mode to online.  The last byte is a CRC  
check of some sort as it changes by exactly one as previous nybbles  
change from 0 to 1 or 1 to 0.

I didn't bother with a differential-to-RS232 converter, I just ran  
J6-9 into a PC serial port RXD.

J6-4 and J6-8 may be the serial input to the 80188 processor.

--------

U101 (the 75174 differential receiver on the mezzanine board) has  
some of its inputs connected to J5-4, J5-9, J6-4, and J6-8.  I have  
not yet traced the 75175 driver next to it.

--------

I have found no outputs on the ALARM connector.

--------

My mezzanine board looks identical to the one in John's pictures  
except the GPS 10 pin header and the antenna bias circuitry is  
unpopulated.   There is +5 present on the header pads where the GPS  
would go at at least GPS TXD and PPS make it out to J5.

I don't have an XO unit to experiment with but it looks almost  
identical to the RB as John has noted.   Like the Z3801 and 3816,  
there must be a way for a technician to check the operation of the  
GPS at deployment time at the cell site - and maybe to put it in  
position-hold mode following a survey.

As the GPS TXD and PPS lines are tied right to J5 on the front panel,  
I am betting that J5 provided a craft interface to the GPS.  I  
cannot, however, find a path for the GPS RXD from the front panel to  
the 10 pin header.  I watched GPS RXD during power up to see if the  
processor on the mezzanine might be sending initialization or status  
query commands and there were none.  At this time I am wondering if  
the mezz. board was only interested in 1 PPS OUT for XO disciplining  
purposes, and TX/RX was carried right to the front panel for setup/ 
testing purposes.

Hope this helps.  YMMV!

73 de JIM N8ECI




More information about the time-nuts mailing list