Hi there, I'm new to this list and have some interest in quartz crystal and rubidium oscillators - GPS, NTP, PPS and "clock watching" in general ;-)
I snatched an R&S XSD frequency standard accompanied by an XKE frequency controller. Found the manuals on KO4BB's site (Thanks a lot for that! BTW there's a slight mix-up of pages in that some of the XKE pages have found their way into the XSD manual). My initial hope of a quick and easy restoration project faded a bit when I looked at the XSD output frequency after heating up the oven. It was off by about -1 * 10-5 and after cranking the fine tuning for some time and having another look at the specs I realized that the frequency was too far off to be dialed in by the fine tuning which only covers about +/- 2 * 10-7. Next step was to take apart the oven and check series capacitor, oscillator and the crystal itself. I found that even the coarse adjustment range of the cylindrical series capacitor (40 - 110 pF) would not allow to pull the crystal to it's specified frequency. When replacing the series cap by a ceramic and lowering the value to just before the oscillation breaks down (about 10 pF) I managed to set the oscillator frequency offset to +2.5 * 10-6 at room temperature. But even this will not suffice when taking into account that the frequency will drop by a few parts in 10-5 (cf. XSD manual) when the oven heats up to its operating temperature. I also checked some of the components on the oscillator PCB which might have an influence on frequency but could not find any fault. The crystal itself is a disk of about 30 mm diameter mounted in a sealed glass cylinder of about 38 mm dia. and 43 mm height. There is no socket just 2 bare wires.. It does not show any visual signs of damage. According to a reference given in the R&S XSD manual the crystal's construction follows a publication from A.W. Warner "Design and Performance of Ultraprecise 2.5-mc Quartz Crystal Units" in Vol 39, Issue 5 of Bell Labs Technical Journal (Sept. 1960). According to that it is an AT-cut 5th overtone design. Now my questions: a) Considering that this gear is about 50 years old, a "crystal gone bad" situation shouldn't be that much of a surprise, right? But could there be any other cause of the "huge" frequency offset besides a bad crystal? I would very much appreciate any idea that I could try to get this baby back on spec. b) if nothing else helps: Could any of you give me a hint about who might be able to supply a spare crystal? I tried my directly reachable contacts but unfortunately to no avail so far. Please consider that similar crystals might also have found their way into other manufacturer's constructions from that era - Sulzer, Racal, HP ... you name it ... Many thanks in advance! Best regards ... Michael U. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
