[time-nuts] Trak 8821B ---- was Z3815A Internal SMA 10Mhz Output

GandalfG8 at aol.com GandalfG8 at aol.com
Wed Aug 22 20:07:11 EDT 2012


In a message dated 22/08/2012 21:30:36 GMT Daylight Time, bg at lysator.liu.se 
 writes:

Hi  Nigel,

>
> With regards to the Oncore VP carrier phase  measurement option, I'm  not
> too sure that the 8821B does  actually make use of that.

The "Z" is a pure software option, to enable  the phase capability already
in all of the VP receivers. So you pay extra,  but get exactly the same
hardware. Since they optimised away IRIG and other  function, I find it
unlikely they would have premium Z options in the VP if  it was not used. I
should try to snoop on the communication between the VP  and the
microcontroller in the 8821.
--------------
 
Hi Bjorn
 

It's obviously difficult to be sure one way or the other without checking  
as you suggest, but I was also taking into consideration some Motorola 
published  data from 1996 and 1998.
 

The information provided in "Oncore Product Summary" of October 1996, and  
"Oncore Model Number and Feature Cross-Reference" of October 1998, is quite  
concise so perhaps nowhere near the whole story, but 
it does indicate that whilst four of the six VP models available in 1996,  
two with the Z option and two without, had a specified 1PPS accuracy of less 
 than 50ns, which was otherwise matched only by the UTplus, amongst the VP 
models  available at the end of 1998 it was now only the Z versions that 
offered this  degree of accuracy.
 

Not only did the 1998 Z versions match the UTplus for 1PPS accuracy, they  
also offered a Differential GPS option which the UTplus did not, although  
perhaps that wasn't over important in this instance, and they were also the 
only  Oncores to offer Raw Satellite Data, again perhaps not particularly 
relevant but  all of which to me still suggests there could have been other 
reasons for  choosing them besides the carrier phase option, which ironically 
isn't even  listed amongst the options in the 1998 "Feature Cross-Reference" 
list:-)
 

 
I'm not trying to make a case either way, just keeping an open mind and  
still as unsure as I ever was:-), but it does seem that when these 8821Bs were 
 produced the three Z versions of the VP were probably the best all round  
performers in the range at that time, and that's not even considering the  
carrier phase option, so perhaps just generally perceived as the best bet  
regardless.
 

Aside from that, I've had my unit powered up for over 90 minutes now  and 
it seems to be settling down ok.
20 minutes or so after power up the status light came on, stayed on for a  
short while, and then proceeded to flash at what seemed like one flash per  
second for another 20 minutes or so before lighting up permanently again and 
 staying on ever since.
I don't remember seeing it flashing before, and so far I've only found  
reference in the 8821A manual to it being either on or off, any ideas on  that?
 

In what way were you seeing GPS problems?
I've got some commands from the manual that produce an error message  
rather than the indicated response but I'm assuming that's a firmware  
difference, and generally all is as I would expect, with regards to satellites  
tracked, position data, etc etc.
What I can't do right now is any accurate monitoring of the output  
frequency or 1PPS, just about everything round here is powered down whilst  I run 
in some new cables, but I would say all is looking pretty good so  far.
 







Regards
 

Nigel
GM8PZR


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