Re: [time-nuts] questions on uncompensated crystal oscillators
The basic criterion are: - used with a VLSI inverter based oscillator with 3.3 V supply, but somewhat high impedance output. An inverter is not specified for oscillator duty. It cannot be analyzed for this application on SPICE. It will never be a high precision oscillator circuit. (10 ppm is high precision when it comes to using inverters). If you care about performance, use a transistor to make the oscillator and use the inverter to convert the sine wave to logic levels. If you cannot use a transistor, relax your specs about an order of magnitude. Rick Karlquist ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] 10811 Extra Lagging etc
Given that HP's engineers have done such a good job with the oven and oscillator design, is there anything to be gained by adding extra thermal insulation (lagging)? How much Not a good idea. The best thing you could do to improve temp stability of a 10811 is to tweak the resistors that proportion the power between the two heater transistors. At some ratio, the thermal gain will peak at over 1000 typically. If you just take pot luck, you would be lucky to do 100. You are still limited by the tempco of the electronics, no matter what thermal gain you achieve at the crystal. You should also be aware that the 10811 is fairly humidity sensitive, which can seem like temperature sensitivity if the humidity and temperature change together. The HP E1938 was a much better design in terms of environmental insensitivity, but that didn't help much because the ultimate stability was limited by crystal frequency jumps, which didn't seem so bad with the 10811 due to the large environment errors in it. In the E1938 they stuck out like a sore thumb. Rick Karlquist N6RK ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
RE: [time-nuts] Phase Comparator
It specifically addresses the gain/bandwidth zerocrossing detector issues. Peter ZL2AYX Also see John Dick's 1990 PTTI paper on JPL zero crossing detectors. Excellent. Rick Karlquist ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
RE: [time-nuts] Xtal Oscillator Aging
It has nothing to do with throwing off atoms. A Xtal is actually a This only happens in very low quality crystals that have impurities on the surface. Going in the other direction, the mechanical resonant frequency changes with time because, as the xtal vibrates, microscopic cracks in the structure of the quartz break apart. Running at high power makes the crystal generate these microscopic faults at a faster rate; this then causes the oscillator to have poorer long-term stability. When an xtal is left vibrating (oscillating) in an undisturbed environment, the rate of cracking of the quartz decreases, and the oscillator is said to age to its final frequency. The 10811 scientists agree that microscopic cracks are the main unresolved issue regarding crystal stability (there are many other possible issues, but they have been beat to death, at least in the top tier crystal fabs). OTOH, at HP we never saw any drive power related aging effects. The drive levels we used had some effect on the frequency (as shown in my E1938 paper) so we were limited because of that issue. Also, the g forces were so high that we couldn't go a lot higher without danger of losing the plating metallization. The effect on S/N ratio is such that you need a certain amount of drive to get a good noise floor at 10 kHz (which is only important in a minority of applications). Close in, the S/N ratio is determined by the quartz not the electronics, and running higher crystal drive doesn't help. It may even degrade short term stability. But if you subject that same crystal to a mechanical jolt will force some new cracks and re-start the aging diffusion process. Ditto turning the oscillator on off or a thermal shock can aggravate the aging. At HP, we never saw any significant aging shift due to turning the oscillator on and off (while maintaining the oven at the same temperature). OTOH, it is definitely true that any oven temperature change will have a settling time effect on aging. If the metal can or glass envelope around the xtal outgasses, some of the resulting crud (a very scientific term!) from the envelope and seal will deposit onto the quartz and also cause aging. For this reason, only the cheapest crystals are housed in a metal can with a solder seal; cold welding of the can is a much better procedure; and a glass envelope is the best. Cheaper than cheap are the WW2 FT243 Many decades ago, glass was the gold standard. However, cold well metal cans have long since superceded glass. Rick Karlquist N6RK (formerly HP Santa Clara Division) ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
RE: [time-nuts] Interfacing a 8dBm sine output of an OCXO to adigitallogic standard
I can imagine that the sine wave must be squared off using a fast comparator and then fed through to a logic driver. Are there any integrated IC's out there that does this? It would be rather sad to sustain substantial phase noise degradation due to a floating comparator threshold and limited slew rate. Stephan Sandenbergh A comparator IC is the worst possible circuit you could use. Especially a fast one. Fast comparators have higher analog bandwidth, which means a greater noise bandwidth for the purpose of noise aliasing. Also, the propagation delay of comparators is very temperature and amplitude dependent (ie AM to PM noise conversion). The simplest circuit that is any good is to simply capacitively couple the sine wave into the clock input of a 74ACXX series logic gate. Use 10K resistors to ground and +5V to DC bias the input to +2.5V. Do NOT use 74HCXX logic for this. We used the 74ACXX trick in the HP/Agilent/Symmetricom 5071A cesium clock at 80 MHz, although it was not in a place that needed extremely low phase noise. The best circuits involve using bandlimited, low distortion, low phase noise amplifiers to produce a large sine wave which is then passively limited with diodes. You can also get away with driving a differential pair with a common current source for the emitters. A classic paper on zero crossing detectors by JPL's John Dick at the 1990 PTTI explains the theory behind all this. Rick Karlquist N6RK ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
RE: [time-nuts] Interfacing a 8dBm sine output of an OCXO to adigital logic standard
http://www.icst.com/datasheets/ics2305.pdf ICS has many interesting clock chips which can be used for other uses than what they were designed. Worth a browse. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 This chip has 200 ps of jitter! There is no way you would want to use this with an OCXO. Rick Karlquist N6RK ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
RE: [time-nuts] Symmetricom 5071A
Never has Symmetricom or any other CBT manufacturer made CBTs for HP or Agilent. HP/Agilent always made their own. I thought the CBT's were originally made by Varian for HP. That's why the CBT burn in fixtures (still in use today AFAIK) are marked Varian Associates. In any event, the 5071 CBTs have never been outsourced. Rick Karlquist ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
RE: [time-nuts] Warning: HP oscillators on eBay from todoelmondo(Ray Mahoney)
, but it looks like a list of numbers folllows this, and not the letter A I'm converned this is perhaps a special, at an odd freqency, and not the standard 10MHz 10811A. Is there any where it actually says 10811A on the package? Can you give me a price to ship to the UK. Address would All 10811's of any flavor have 10 MHz outputs. (Except an extremely small number of prototypes at 10.23 MHz for a GPS initiative that were never released AFAIK). If you know anything about making an SC cut crystal of the quality of the 10811, you would know that changing the frequency requires a huge RD investment, way beyond what any special could justify. There are basically only three models of 10811 made: 1) With PC edge connector 2) With coax connectors 3) Special for the 5071A with extended tuning range, which is unlikely to show up for sale. All 10811-6 are simply selections of one of the above. After a lot of time has gone by, these selections are, for the most part, irrelevant. Model 10811A is a nomenclature used in cases where an oscillator was sold directly to the end user as a component. HP was briefly in the merchant oscillator business. The vast majority of 10811's were for internal use. They all have 10811-6 numbers. Many of the 10811-6 numbers are selected to meet tighter specs than the 10811A spec. There is nothing superior about an oscillator labeled 10811A. BTW, it was superceded years ago by the 10811D/E, in terms of model numbers. Rick Karlquist RD Engineer at HP Santa Clara Division 1979-1998 ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
RE: [time-nuts] connections for HP 10811A ?
-Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Chuck Harris Sent: Wednesday, April 20, 2005 8:14 PM To: [EMAIL PROTECTED]; Discussion of precise time and frequency measurement Subject: Re: [time-nuts] connections for HP 10811A ? I imagine that that is because HP just went on the warpath, and declared all copies of their manuals verboten. I just got several notices from ebay telling me about how some HP manuals on CDs that I bought were infringements on HP's intellectual property. This was old stuff too, from the early '70s -Chuck The Agilent Library in Palo Alto is working on a project to make HP/Agilent manuals available in .pdf form. I donated 100's of my manuals to their collection. They are scanning them in. I don't know the exact method by which an outside person accesses this collection, but I was told it was in response to many customer phone calls about manuals. Rick Karlquist N6RK (employed by Agilent Technologies) ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
