[time-nuts] pp2s? No, 1pps from a Nortel GPSTM!

EB4APL eb4apl at gmail.com
Wed May 27 15:35:22 EDT 2015


Hi,

I have another Thunderbolt cousin, a NTGS50AA.  For a long time I 
desired to have 1PPS from it and even I asked this list for a cue, the 
responses were negative, some thought that there were no 1PPS outside 
the big chips.
My unit developed a problem and troubleshooting it I found the wanted 1 
PPS at TP-33 coming from U2-76.  Given that this GPSDO has two outputs 
whose usefulness is dubious, 1/2 PPS and 9.8304 MHz (we don't have a 
CDMA tower, do we?), my plan is to use one of these outputs for the 1PPS 
signal.  Both outputs have drivers that are identical so probably I will 
cut the 9.83404 signal just before the driver and solder a piece of wire 
wrapping wire from TP-33 to the driver input.  In that way I will have 
1/2 PPS and 1 PPS on the output connectors.
I have checked that the 1PPS is totally synchronous with the 1/2 PPS, I 
don't have means of properly check the jitter between both signals but a 
scope shows no jitter at all.
The above mentioned problem became worse and finally I had to replace 
the whole thing.  Fortunately a member of this list kindly offered to 
sell me one of this spare units and now my reference is working fine.  
As soon I have a time gap I'll do the modification and publish the pictures.

Regards,
Ignacio


El 26/05/2015 a las 14:09, Tom Van Baak wrote:
> Hi Nate,
>
> Nice page. Thanks for sharing your work.
>
> The Nortel units are a reasonable and slightly cheaper alternative to a TBolt, if you don't mind the much larger size, mass, and non-standard connector issues.
> The performance depends somewhat on which vendor's oscillator was used. I tested a bunch here:
> http://www.leapsecond.com/pages/nortel/
> For NTP none of these plots matter (most GPSDO are a thousand to a million times more stable than NTP or a PC can handle).
>
> /tvb
>
> ----- Original Message -----
> From: "Nathaniel Bezanson" <myself at telcodata.us>
> To: <time-nuts at febo.com>
> Sent: Monday, May 25, 2015 7:08 PM
> Subject: [time-nuts] pp2s? No, 1pps from a Nortel GPSTM!
>
>
>> As anyone with a Nortel GPSTM knows, it's a close cousin to the Thunderbolt but not exactly identical. Notably, coming from a CDMA environment, the unit has an "even second" output, aka PP2S, aka 0.5pps, aka 0.5Hz, etc. (Hoping to make this searchable...) There are software commands to configure this on the Thunderbolt too, but the GPSTM appears to have this function hard-coded into the PAL, and it can't be set back to PPS in software.
>> However, there exists a PPS signal on the PCB, at TP13 between the Trimble chip and the PAL, discovered by some folks at the hackerspace here, during some noodling-around with an oscilloscope this afternoon. It's all documented here:
>> https://www.i3detroit.org/wiki/Nortel_GPSTM
>> This is for a NTBW50AA-11 module (single long board), other parts may have the signal in different places but I bet it's in there.
>> Enjoy!-Nate B-
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