[time-nuts] Lucent KS-24361 GPSDO arrived today several questions

Bob Camp kb8tq at n1k.org
Thu Nov 6 19:07:52 EST 2014


Ok, I got to spend a little quality time with my pair today. I mostly poked at the Diag port with a terminal program. 

Both of the units seem talk over the Diag port regardless of the mode they are in (master / slave / fault ). Both respond to a sub-set of the Z3801 SCPI commands (= not all commands work). There are a few enhancements where a query to a “node” gives a reply (which it should not if it’s “node only”). All of it works ok at 9600 baud 8N1. All of it comes back with an error message (E-xxx) after a valid command response. It may not like the terminal program sending cr/lf or something like that. 

By far the most useful thing to type is :SYST:STAT? 
That executes the system:status request and gives you a nice full screen of information. It shows you about 95% of the useful information all on one page. About the only major thing missing is the DAC value. That’s available with another command out of the Z3801 list. It does take a while to compose and transmit the screen, so it’s not the best way to to this forever and ever.

The data from the request is the same on both boxes. Same everything except one shows as standby etc. The interesting details are things like elevation mask and cable delay. Why interesting? You can set them with discrete commands. You can also query the data with the same commands to make sure the box “took” what you sent. 

This allows experimentation with changing the elevation mask on each box (or just simply doing a discrete query for the mask on each box). The Ref-0 / slave will happily change things around with discrete commands. None of them are reflected in the :SYST:STAT? listing on the Ref-0 or Ref-1. When you look at the Ref-1 / gps box, it’s discrete query information matches the :SYST:STAT? screen on both boxes. When you change things on the Ref-1 box both screens follow that data. 


When you pull the antenna on the gps box, it immediately (almost) goes into gps fault led flashing mode. The slave box happily sits there for a while (say a minute) with it’s gps led saying all is well. When you plug the antenna back in, the process is reversed. The gps box goes out of flash mode right away. The led goes out in a bit. The led on the slave box does not follow for a minute or so. 


All of this suggests to me that the Ref-0 / slave does not talk back to the other box via serial. It also suggests to me that all it “sees” from the Ref-1/gps box are the duplicates of the serial string out of the Motorola gps module. The Ref-0 just figures out what’s happening by watching those strings as they roll by.

Hope that makes sense….


If that’s all true, it should be “easy” to put dummy gps sentences into the Ref-0 interface port and a pps from something else. Once it sees stuff that it likes, it will start locking up to that pps. Cheap micro and just about any modern gps = fancy new GPSDO. Quick / easy / not much work. A little more complex if you decide to translate sawtooth data. That of course assumes these boxes do anything with sawtooth ...


> On Nov 6, 2014, at 7:52 AM, GandalfG8--- via time-nuts <time-nuts at febo.com> wrote:
> Hi Bob
> I view the master/slave situation the same way you do, but only  commented 
> because Lucent effectively sets things up the other way round so just  
> wanted to be sure which way Paul was considering it.
> As regards, the "faking", yes, a single 15 way plug containing just  a link 
> and a resistor is exactly what I use now.
> I realise the RS422 fudge isn't ideal but certainly very handy for some  
> quick tests.
> I've got two or three RS422 PCI interfaces but hadn't previously had any  
> spare slots, now I've got a couple of lovely Magma 13 way PCI expansion units 
> but need to hack them about so the ports are at the front.
> Whoever decided rack mount PC kit should be built with all the  connections 
> at the rear must have been really nuts, and it was too long ago  to use 
> "corridors" of racks as a viable excuse, someone somewhere just fitted  ears to 
> desk top style cases and left the rest of us to get on with  it..
> One of the best things I ever did was to buy a pair of "back to front"  
> rackmount PC cases with all ports and cards available at the front, trouble is  
> now I want everything else to match, and most test gear has just the same  
> issues!
> All good fun, and certainly never a dull moment:-)
> Regards
> Nigel

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