At a hamfest a few of weeks ago I got a TrueTime XL-DC, with antenna and
feedline for $45. :-) With the antenna setup in my living room it works
great, in good weather. It's the 1U version, with only the center LCD
display. The IRIG-B output works. I found a manual at
https://web.archive.org/web/20161222211531/glacier.lbl.gov/gtp/DOM/Support/xl-dc-manual.pdf.
There is also on at
https://web.archive.org/web/20161226212915/https://ics-web.sns.ornl.gov/timing/151-652-893man.pdf,
but it's newer than my unit. The manual shows the unit labeled as
Symmetricom. with a large LCD for the time/date only and the small LCD.
Mine is labeled TrueTime and has only the small LCD. The manuals do not
have any information on the option cards. Is that documentation on the
web anywhere?
I have two option cards. One is an NTP card, labeled NTL-XL 87-6003-XL,
with an AUE Ethernet port.
The second card is labeled “HAVE QUICK II” 86-396-3 and has one of three
BNC connectors installed. A scope shows that it puts out a low speed
serial digital signal. Does anyone know what this card is for? The US
military has a secure radio system named Have Quick, everything Google
turns up is for that.
Can I upgrade this unit with one of these cards, to get 10 MHz output?
https://www.ebay.com/itm/Used-Truetime-XL-DC-GPS-Time-Frequency-Receiver-Module-Card-85-600-Rev-C/312792439289
It's made to go into the larger 2U version. If I remove the top bracket
it will fit in my unit, but will it work?
Is the 10 MHz output a GPSDO?
On my unit Function 71 shows on the LCD display:
Osc Phase, I see numbers +/- in the range of e-9 to e-10. It updates at 2 Hz
Osc Offset, same as above but the scale is +/- e-10 to e-11, sometimes
down to e-14. It also updates at 2 Hz
Osc Drift is of the order of 10e-9 per day. It updates at 2 Hz, or slower.
DAC is -17645, +/- 30 or so, and it doesn't update/change very often.
Respone Time 1.250E+01 seconds. It does not change, and the maual makes
to mention of it.
Manual:
"Oscillator phase" is the instantaneous error between the XL-DC timing
outputs and GPS.
"Oscillator offset" is the frequency offset or error with respect to the
GPS frequency
"Oscillator drift" is the change in oscillator frequency per day.
"Oscillator DAC" is the signed 16 bit DAC control integer which sets the
DAC output voltage to control
the internal or external oscillator.
On this list the next question is, how good is this? Looking at the
manual and inside of the unit I think
it has just a TCXO.
I will use the 1 PPS output to drive a Shera board.
Thanks
Robert
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