[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
> 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.
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"
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
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.
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