Re: [time-nuts] 10811 Extra Lagging etc
In message [EMAIL PROTECTED], Richard \(Ric k\) Karlquist writes: Wasn't humidity also the main source of trouble with the cesiums ? -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [EMAIL PROTECTED] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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
The 5071 cesium has no measurable environmental sensitivity to temperature, pressure, or humidity, down to a measurement threshold of 1 part in 10^15. The 5061 cesium had various environmental sensitivies due to the harmonic generator. This generator was far more efficient than any other I have studied (and I spent too much time working on SRD frequency multipliers). It was designed by a Korean professor and no one at HP really understood the magic in it. Being so highly optimized, it was fairly temperamental. Also, the joints leaked RF due to silver tarnishing, etc. Thus RF leaking out then back in could be affected by the environment or removing the top cover. The 5061 had a frequency coefficient of microwave power that doesn't exist in the 5071. It wouldn't surprise me if humidity affected the 5061, although I don't have any direct evidence of it. Rick Karlquist N6RK Poul-Henning Kamp wrote: In message [EMAIL PROTECTED], Richard \(Ric k\) Karlquist writes: Wasn't humidity also the main source of trouble with the cesiums ? -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [EMAIL PROTECTED] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ 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
packaging machinery design. The sugar wafer used in that product was highly hygroscopic. The main reason that product failed was that we weren't able to achieve sufficient shelf life despite trying all sorts of quite expensive multi-layer metallized wrapping paper. Even the multi-layer metallized stuff was moisture-permeable enough that the wafer would go soggy after a couple of weeks. John Rick N6RK Have you noticed that in recent years, Pop Tarts come in aluminized mylar pouches? I always find this a rather humorous use of space technology. ___ 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
Water vapor is actual water, simply in gas form, so if the temperature drops quickly after a high humidity day, the vapor inside the bag will condense before it has time to escape and you will get actual water in liquid form in the bag, in the form of condensation. Easy to do in Florida, happens every afternoon in the summer. I suspect your humidity sensor peaks at 95% because of hardware/software limitations, not because of conditions inside the bag. Didier Neon John wrote: On Tue, 20 Jun 2006 17:54:46 -0700 (PDT), Actual water can't penetrate the bag so when the humidity is condensing, the inside-the-bag unit peaks at about 95%. John ___ 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
Yes, I did, because nobody else had, and I was curious. We were seeing changes along the lines of parts in 10^8, about an order of magnitude worse than tempco. This was for something like dry nitrogen purge all night vs 50 degrees C, 90% humidity for an hour or two. Does anybody understand the mechanism? I assume the actual crystal itself is sealed. I'd guess that something in the control electronics in humidity sensitive. Do FR4 boards change size with humidity? Is the thermal conductivity of humid air enough different from dry air to change the internal temperature of various parts? -- The suespammers.org mail server is located in California. So are all my other mailboxes. Please do not send unsolicited bulk e-mail or unsolicited commercial e-mail to my suespammers.org address or any of my other addresses. These are my opinions, not necessarily my employer's. I hate spam. ___ 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
TVB noted: If you are using the 10811 as part of a GPSDO the PLL should take care of any number of slow-moving changes in frequency; whether it's temperature, humidity, voltage, OCXO ageing, DAC drift, phase-of-the-moon, etc. So I don't see a compelling need to protect the OCXO in the ways being proposed. If you are in a harsh, or fast-changing environment then do the math to see if your OCXO dF/dt exceeds what the PLL can close relative to the dF/dt of the GPS reference. There are several elements of the GPSDO that can have sever temperature sensitivity: 1. The GPS receiver itself. Of particular concern is the group delay thru the ~2 MHz wide IF filters and also the several MHz wide filters in the RF front-end. The IF filters are often SAW (Surface Acoustic Wave) devices, and the RF bandpass filters are frequently coaxial ceramic devices (functionally similar to tuned cavities, but built inside high dielectric constant ceramic). I have seen tempco's of as much as a few nsec/ºC for some brands of receiver boards. 2. The GPS antenna. Most systems employ patch antennas which are manufactured with ceramic dielectric loading of the patch elements. Since these are located outdoors, they can see several tens ºC temperature swing throughout a day. 3. Most GPSDOs use a fairly long divider to bring the standard oscillator down from 10 MHz to 1 PPS. If you use ripple counters for these dividers, they will show a significant temperature sensitivity. I once used a string of 3½ 74HC390's to bring 10 MHz down to 1PPS and was appalled to find several hundred nsec of delay change with ambient temperature in a trailer. But when you realize that 7 BCD counters with 4 flip-flops each account for something like 72 CMOS gates, each with a tempco ~1 ns/ºC, the results were not surprising. The moral to this story is that the counters in your GPSDO should be synchronous counters. Better still, I found that TVB's single chip PIC divider had unmeasurable temperature effects. I would be surprised if you find a significant humidity or pressure pull unless you have a problem with moisture condensing on some component; the dielectric constant of liquid water (or ice) differs significantly from unity! 73, Tom ___ 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] 10811 Extra Lagging etc
Hi Brian, I went through what you are about to embark upon. Some comments: * My 10811A has about +-2Hz EFC adjustment range 0-5V. I used the mechanical adjust to have about 0Hz offset at 2.5V EFC. Make sure your voltage reference for your DAC is temperature stable (5ppm per Celcius), otherwise the error is from the DAC/Reference, not the OCXO. It is best to somehow put the DAC and DAC-reference inside an oven as well, or at least thermally connect it to the oven case etc, so that it doesen't experience your expected 35 Deg C changes. * Insulating the oven does help slow down the effects of thermal changes, but don't overdo it because at high temperatures in the summer you don't want to have the heater turn off completely, and the oven overheat itself just from the internal power consumption of the oscillator itself. Thus you always want some thermal energy to escape through your insulation even at the highest expected ambient temperatures. * Buffer the sine output to mitigate the effects of loading on the OCXO * Provide a clean, temperature compensated power supply to the OCXO. A trick to use: measure the oven current. It should always vary with temp changes, if it stops varying and stays constant while the temp is still rising the oven is temp-saturated. Good luck, Said ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] 10811 Extra Lagging etc
I am about to embark on construction of a GPSDO using the Shera controller and a 05328-20027 HP board based around a 10811-60111 OCXO. GPS is a Jupiter-T. 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 improvement (if any) can be achieved? How much lagging (if any) have people employed. My shack is not air conditioned and the HP board will probably end up in a simple metallic enclosure. Annual temperature extremes range from about 0 to +35 Celcius. My workshop is not very flash and any extra lagging would probably be confined to some bits of foam glued together. The HP board is labelled series 2224. What does this mean? I am yet to measure the VCO sensitivity, but am expecting something around 1x10E-8 per volt. What is a typical value for the 10811-60111? I note that Shera's QST article refers to using the 1 MHz output from a HP5328A. Is there any degradation of performance or increased thermal sensitivity due to the use of a HP marked 7490 (ripple counter) to divide down to 1 MHz? Would use of a synchronous divider or the TVB PIC approach yield a worthwhile improvement? Shera's performance graph shows a reasonably strong diurnal component. I was planning on cutting the PCB track going to the earthed end of the fine adjustment 10k pot and connecting this to the controller. Is there a neater way to achieve this connection? Thanks, Brian VK4GTW ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
