[time-nuts] RFTG-m-XO experiences
Rich and Marcia Putz
rputz at bnin.net
Tue Feb 6 20:09:33 EST 2007
I'll give my experiences with my RFTG unit. I bought it ($$$) last fall from an ebay seller who moves a lot of time and frequency related items, it won't take much imagination to figure out who I'm speaking of. I believe he is an honest seller, and I've bought from him several times and would buy from him anytime again. On the other hand since he moves a lot of equipment I think he writes descriptions as he believes things are and not in a position to actually verify everything that's said. But that's the way ebay is, caveat emptor! I have only the RFTG-m-XO.
The unit I received looks as if it were new old stock, it has '95 date codes on many of the parts, it sports a Piezo Crystal Company OCXO.
When powered up and connected to an Agilent 58532 antenna, fed with 1/2" heliax, with a reasonably clear sky view, after about 10-15 minutes the no GPS and fault lights extinguish, the green on light appears. Receiver outputting 1PPS. Sounds good huh? Upon checking the oscillator I find it running about 8hz low, and after 48 hrs, 8hz low! Having tweek-itis, I adjusted the trimmer on the OCXO but could only move it a few hertz higher. Next thought, maybe if I provide 10 Mhz from another standard to the input it will lock onto that and start working, 24 hours later, 8hz low!
Pondering what could be going on, I measured the EFC voltage to the OCXO and noticed it never rose above about .64v. So I broke the EFC line and the Oscillator EFC voltage (measured on the osc side of the break) floated to about 3 volts and the oscillator moved right up to 10.0000Mhz. What I've discovered is that my RFTG appears to be in "sleep" type mode, here's why I think this; with the unit facing you, there is a test point connector on the back left hand corner of the mezzanine board. (TP-400). The only voltage present on that connector is +5 volts. There is circuitry near TP-400 to provide the + & -15 and the 5 volt reference voltages but they are not being supplied with the required operating voltages. These voltages are likely required for the ADCs and DACs that control things. My thought is, the PLD gets some control signal from somewhere to enable all that circuitry. The "interface" connector probably figures in this also. When this happens the unit will may come to life, and do what it is intended to do!
Conclusion, until we (the time-nuts) get some documentation, especially schematics and commands, we are probably wasting time, and possibly even harming the units by probing around in it , which I've done a lot of.
The units were made by Efratom, which has now become part of Symmetricom, I got to think, someone around here has to know someone else who has had factory experience with these, but until such a person comes forth I think we're flying blind.
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