[time-nuts] Questions on Nortel Trimble NTBW50AA GPSTM

EB4APL eb4apl at gmail.com
Thu Aug 25 17:33:10 EDT 2016


Sorry for this late response but I was away from home.
I did the 1 PPS mod a year ago. I just cut the trace between TP14 and 
U405 pin 6 and soldered a wire between TP14 and TP33.
Now you have 1PPS on the former 9.8304 MHz output. Not being a cellular 
tower operator I did not have any use for this frequency.
Comparing the 1PPS with the .5 PPS pulses, there are an offset, which is 
not constant.  In my case it can be 540, 440, 340, 240 or 140 ns, it 
changes before locking but after the lock condition it remains constant. 
Studying the circuit and the Nortel specs, the 1/2 PPS must be 
synchronous with the 9.8304 MHz signal, so this is probably the cause.  
I still have to check with an independent  1PPS reference (a Rb one) to 
see if this PPS is reliable.

Ignacio EB4APL

El 10/08/2016 a las 21:25, Clay Autery escribió:
> 1) Need a 24 VDC power supply.  Am considering just buying an Astron
> VLS-35M Adjustable Voltage/Current supply (5-32V/1.5A to limit) since I
> don't own a variable power supply yet, this is a linear, and the same
> size package as my RS-70M.  I can worry about a dedicated supply later
> if I decide to keep this GPSTM after I finish modding/testing it.
> Anyone have any recommendations to the contrary?  Why?
> 2) Need to bring the PPS out from the TP in this article:
> https://www.i3detroit.org/wiki/Nortel_GPSTM  The article shows a buffer
> circuit being used to accomplish this...  Need help locating a datasheet
> on the Motorola chip used...  It's obsolete and I need to find a pin
> compatible replacement...
> Or, I need to find another buffer schematic/plan,
> Or, alternatively....  has anyone ever tried pulling the 1pps out and
> hooking it to the 9.8 MHz driver (severing the drive line to it and
> jumpering in the 1pps)?  The 9.8MHz and the 10MHz signal out ports SEEM
> to use identical driver/buffer circuits on this board...  Seems like a
> possibility...
> Preferably, I find the Motorola chip, copy the buffer circuit and move
> on...
> I'm pretty new at this, so any help is appreciated, and not slapping me
> about for "not knowing" stuff is greatly appreciated!  :)
> Sincerely,

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