[time-nuts] Nortel GPSTM TP13 positive or negative?

[Taka Kamiya]

No.  Mine is NTBW50AA-07.  I have no idea what the differences might be.
Yes, I also tried to re-purpose CDMA clock like you did.  Disconnected 9.8304MHz by removing a jumper chip near the buffer IC 7404.  Then I cut a trace so 9.8304MHz is not fed to any of the gates in that IC.  Feed an output from TP13 into one of the pads from removed jumper.  I interpreted various forum and mailing list posting that way, so I tried to do the same.

That didn't work very well.  I ended up with negative logic.  It functions; though, because basically, end of pp2s becomes the rising edge.  This is wrong and timing is not guarenteed.  Also, what I did killed pp2s as well as 9.8304MHz.  I undid all that and restored it to the way it was.

New method is, I built a board that takes the SAME input from TP13.  Using 74AC04, feed it to one gate.  Then feed that output to another gate.  THAT output goes to 2 gates at the same time.  Out from THAT is going to 100 ohm register each.  The other end of the registers are tied together and goes to BNC for output.  That gave me very clean and narrow PPS.  In retrospect, I could omitted the first two gates but I have no idea what kind of load PPS generation logic can take, so to be safe, I am buffering it.
Does that help you?  

--------------------------------------- 
(Mr.) Taka Kamiya
I'm stuck in a wormhole....  Hello, worms! 

    On Saturday, April 13, 2019, 9:00:19 AM EDT, EB4APL <eb4apl at gmail.com> wrote:  
 
 Hi,

I have a NTGS50AA, is this the model of your unit? If yes, I am very 
interested in the circuit diagrams since I have a very partial one, 
which I made by reverse engineering to bring the 1 PPS out, re-purposing 
the 9.8304 output circuitry since I don't have any use for it.

Regards,

Ignacio


El 13/04/2019 a las 6:29, Taka Kamiya via time-nuts escribió:
> There is a typo in my first post.
> TP13 as well as one pulse every 2 second output are negative logic.  Manual does not mention polarity of 2sPP.
> On this page: Nortel GPSTM - i3Detroit  if I'm reading the circuit diagram correctly (really a construction diagram), he seems to be inverting it once, then feeding it to parallel of another inverters.  If I do this, I get negative 1pps.  I cannot make heads or tails out of scope screen shot as I have no idea (I can only guess) which trace represents what output.  But green line is showing negative logic.
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> ---------------------------------------
> (Mr.) Taka Kamiya
> I'm stuck in a wormhole....  Hello, worms!
>
>      On Friday, April 12, 2019, 11:01:02 PM EDT, Taka Kamiya via time-nuts <time-nuts at lists.febo.com> wrote:
>  
>  I was fortunate enough to buy Nortel GPSTM at very good prices.  This is a distant cousin of Thunderbird as far as I know.  However, it being CDMA clock source, it's second pulse output is actually once every 2 seconds.  According to various Internet sources, TP13 on board is 1 PPS.
> I measured TP13 and it actually IS 1 PPS.  However, this test point is giving negative logic.  Normally +5V and it goes to 0V every 2 seconds.
> Manual does not say anything about this being PP2S (with a bar on top).
>
> Has anyone noticed this or am I doing something wrong????
> I cascaded two inverters (74AC04) and have used two gates to provide boost to obtain normally 0V and goes to 5V every 1 second.  It works but I am baffled.  Can anyone tell me what I am seeing is actually the way it is?
>
> ---------------------------------------
> (Mr.) Taka Kamiya
> I'm stuck in a wormhole....  Hello, worms!
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