Re: [time-nuts] Comparing the BeagleBone Black Raspberry Pi asNTP servers
david-tay...@blueyonder.co.uk said: I was really interested to see how much effect the extra Ethernet latency of the Raspberry Pi added in a real-world scenario. Thanks to Philip Gladstone, I have now discovered a way of significantly reducing that latency, so that the delay reported by NTP is reduced from ~0.51 to ~0.35 milliseconds. http://www.satsignal.eu/ntp/RaspberryPi-notes.html#EthernetLatency Thanks for the tip. I did that to my R Pi and I see the same improvement in round trip time. What I don't understand is why the time offset as measured by an outside system didn't change. ?? -- These are my opinions. I hate spam. ___ 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.
Re: [time-nuts] Comparing the BeagleBone Black Raspberry Pi asNTP servers
From: Hal Murray http://www.satsignal.eu/ntp/RaspberryPi-notes.html#EthernetLatency Thanks for the tip. I did that to my R Pi and I see the same improvement in round trip time. What I don't understand is why the time offset as measured by an outside system didn't change. ?? Perhaps because NTP sees the offset in both send and receive packets and therefore, like any other network delay, it is subtracted out. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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.
Re: [time-nuts] Comparing the BeagleBone Black Raspberry Pi asNTP servers
On Wed, Mar 25, 2015 at 3:22 AM, Hal Murray hmur...@megapathdsl.net wrote: What I don't understand is why the time offset as measured by an outside system didn't change. ?? NTP always and continuously measures the round trip time over the network and assumes the one-way time is 1/2 the round trip time. Reducing the latency reduces the round trip time that NTP has to compensate for. So if NTP always compensates for network delay why do you get improved performance with less delay? That is because what messes up NTP is uncertainly in the delay and likely it's the case that reducing the delay also reduces the standard deviation of the delay. The other thing the messes up NTP is its assumption that the delay is symmetric (that the one-way delay = one half the round trip delay) I think reducing the round trip time also reduces error in this assumption. NTP is not magic and uses the same algorithm you would use if you lived 200 years ago and were told to synchronize two grandfather clocks in two houses that were 1 mile apart and you have to walk between the two houses and you had no third clack you could cary. What is the optimal solution to this problem: I think your first step would be to walk the distance many times to build up a statistical database for travel times to get a solid mean and sigma. Then you would walk back and forth, 24x7 and try to compute the differed in rates of the two clocks and adjust the pendulum of your clock. Setting the absolute time would not work to converge the error to zero setting the rate would. Of course the best thing would be to buy small clock you could take with you but NTP was designed to run on a dump network that only moves data without timing it. -- Chris Albertson Redondo Beach, California ___ 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.
[time-nuts] Greenwich Timekeeping
For those of you near London with an interest in Greenwich, Harrison, and pendulum clocks there's an event on April 18 that might be worth your time. Harrison Decoded: Towards a Perfect Pendulum Clock http://www.rmg.co.uk/whats-on/events/harrison-decoded http://www.rmg.co.uk/sites/default/files/harrison_decoded_draft_programme_250215-3.pdf /tvb ___ 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.
Re: [time-nuts] Obscure HP T/F instruments in ebay.fr
The HP101A and 5275A arrived today. The 101A warmed up in about an hour and the crystal temp settled. It's now reading 98.50 against my 53131A (med. stability option but uncalibrated). I'm not sure what the spec is, or how long ago it was tuned - but even if it was set recently, it's still survived a DHL truck from france with little error. On Sat, Mar 21, 2015 at 8:05 PM, Bill Byrom t...@radio.sent.com wrote: Warning: Discussion of old pre-1980 technology follows ... The Computer History Museum in Mountain View, CA, is amazing. I wish I hadn't sold my original issue Commodore PET 2001, but you can find examples of this and a wide range of early computers from the 1940's/50's/60's/70's (such as SAGE and CDC6400/6600) at the museum: http://www.computerhistory.org/ They have an operational Babbage Difference Engine No. 2: http://www.computerhistory.org/babbage/ I have worked for Tektronix for 28 years. Many of you may be interested in the vintageTEK website: http://www.vintagetek.org/ For those of you who have read old Tektronix service manuals with schematics: http://www.reprise.com/host/tektronix/humor/ Only a few of us existing Tektronix employees have been with the company long enough to have been involved in selling and supporting analog CRT oscilloscopes, TM500/TM5000 modular equipment, and the Tek 4051/4052/4054 (first all-in-one graphic desktop computers). Some of these were obsolete years before I started Tek in 1987, but I was using them in the late 1970's. When I was a University of Texas Electrical Engineering student back in the mid-1970's I built a device to compare the 3.5795454 MHz color burst NTSC television signal (from a normal TV set color reference oscillator) to an ovenized 5 MHz crystal oscillator using a 315/88 ratio TTL divider in the PLL. I used my Tektronix government surplus RM45A + CA plugin oscilloscope for this project. I also experimented with WWV 5/10/15 MHz frequency comparisons, but in Austin Texas the propagation from Ft Collins CO made this difficult to much better than 1 part in 10^7. The color burst method let me make use of the major TV network's rubidium standards. Unfortunately, by the late 1970's the networks were reading the monthly time deviation reports from NBS (name of NIST before 1988), and they would often manually readjust their rubidium standard magnetic field to get the frequency error in the NBS comparison closer to zero. Of course, this made the reliability of the time dissemination (phase of the color burst signal) unreliable. If they had just let the rubidium standard alone in a stable environment with no temperature or magnetic field changes, the drift in the timing error could have been modeled and corrections to the received signal made before reading the NBS monthly error reports. In my first job (late 70's to early 80's) we used Tektronix 7000 series CRT scopes to compare the output of a Tracor rubidium standard with a WWVB receiver and reference clocks in test instruments we were calibrating. We were considering building a commercial product based on my color burst recovery technique, but the random frequency adjustments by the networks and the switching between network and local station color burst reference clocks during local programming insertion caused us to abandon this project. This was about 7 years before I started at Tektronix. -- Bill Byrom N5BB On Fri, Mar 20, 2015, at 12:02 PM, Robert LaJeunesse wrote: While it may not be time-nut centric there is a great museum in Michigan that has collections of both clocks and technology, along with a couple Stradavarius violins and machinist tools used by Mr. Daimler. The Henry Ford Museum in Dearborn, MI has been actively enlarging their technology collection - having recently paid nearly $1 million for an original Apple I built by Jobs Wozniak. They also have Robert Moog's prototype music synthesizer. Might be time to interest them in adding precision time to their clock and technology collections. Bob LaJeunesse Sent: Friday, March 20, 2015 at 1:33 AM From: Bill Hawkins b...@iaxs.net To: 'Tom Van Baak' t...@leapsecond.com, 'Discussion of precise time and frequency measurement' time-nuts@febo.com Subject: Re: [time-nuts] Obscure HP T/F instruments in ebay.fr There are worse things than breaking up a collection. The Baaken Museum of Electricity in Life, near Minneapolis had a wonderful series of devices that used electricity to examine or prolong life, or to extract money from suckers. About 20 years ago, someone felt that there wasn't enough traffic at the museum, so the interesting exhibits were removed and the museum dumbed down for children. A vampire might greet you at the door. It seems that modern business managers have no time for things that don't draw crowds or fly off the shelves. If a museum or business wants to serve a market niche, it must compete with the
Re: [time-nuts] Comparing the BeagleBone Black Raspberry Pi asNTP servers
On Wed, 25 Mar 2015 09:46:05 -0700 Chris Albertson albertson.ch...@gmail.com wrote: So if NTP always compensates for network delay why do you get improved performance with less delay? That is because what messes up NTP is uncertainly in the delay and likely it's the case that reducing the delay also reduces the standard deviation of the delay. The other thing the messes up NTP is its assumption that the delay is symmetric (that the one-way delay = one half the round trip delay) I think reducing the round trip time also reduces error in this assumption. There is another assumption, that most people (especially engineers) do (and NTP is forced to do), which does not always hold true: that measurement noise is mean-free and uncorrelated. Especially in this case, USB delay is definitly not mean-free if you queue up packages (i would go so far as to say, that USB induced delay is never mean-free) and has a non-zero auto- and cross-correlation, mediated trough the USB clock, which is synced to the system clock's source (they are derived from the same crystal). AFAIK, and without checking, I think that NTP also makes the assumption, that the noise is ergodic and time-invariant during measurement. Again, in the case of USB (and to some extend all network based communication systems), this does not hold true. Attila Kinali -- _av500_ phd is easy _av500_ getting dsl is hard ___ 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.
Re: [time-nuts] Comparing the BeagleBone Black Raspberry Pi asNTP servers
What I don't understand is why the time offset as measured by an outside system didn't change. ?? david-tay...@blueyonder.co.uk said: Perhaps because NTP sees the offset in both send and receive packets and therefore, like any other network delay, it is subtracted out. The description of the change was to remove a delay on the receive side. There was no mention of a change on the send side. So I was expecting a change in the symmetry. (I don't know if it would make things better or worse, but something should change.) -- These are my opinions. I hate spam. ___ 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.
[time-nuts] Lucent RFTG-m-XO failure to obtain GPS signal
Have two of the late 90's Lucent L106B boxes. They are isolated except for power and GPS antenna connections. I've read the manual and the archived timenuts material that I can find with Google. My test equipment is limited to a counter and an oscilloscope. Have computers but no S/W. DVMs, of course. Both power up. After about 15 minutes, the red FAULT light goes out and the green ON light is lit. 15 MHz appears at that outlet, six zeroes to the right of the decimal point. The Efratom XO is similar. The NO GPS light never goes out, except to blink when the antenna is disconnected. Let it run 16 hours, no joy. The manual (for earlier devices) says it will initiate a field survey on its own, if it needs to. The antenna is a Garmin low profile 3 unit, part number 00-89002-000. Google and the Garmin site can't find it. It seems to draw enough current, since the device knows when it has been disconnected. I no longer have any way to test the antenna, so I need to look at the fault code from the receiver. The receiver, presumed to be some kind of Oncore (the numbers on it don't help) is in a metal box on a daughter board with a Motorola 68331 micro. Is there a way to tell what's going on without hacking it from the basic bits? Would really like to solve this problem. Failing that, does anyone want them? Have the matching L105A RB boxes, which fire up and produce 15 MHz. Also female BNC to male SMA adapters. Many pictures available. Thanks for any help. Bill Hawkins ___ 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.
[time-nuts] Sphere Research's annual Stuff Day is next week!
Just a reminder, Sphere Research's annual Stuff Day is *next week*, April 3rd (friday) and April 4th (saturday), 9am to 4 pm. There will be (literally) tons of free stuff, plus some great test gear for dirt cheap prices. if you need more info, please look here on our webpage: http://www.sphere.bc.ca We are in West Kelowna, BC, Canada, just 4 hours from Vancouver or Seattle. tons of interesting HP stuff, including some free hp 436A and Boonton power meters, spectrum analyzer eyebrow converters, 8620C sweepers and spare scales, all kinds of nifty things. Please remember to bring your own boxes and bags for parts. we have gazillions of new parts in bulk and on reels. Also, lots of vacuum tubes for the filament fans. There's a big box of free tubes, take all you like. There's a big pile of Tek, HP and Philips manuals, just $2 each, plus some nice scopes, plug ins and yes, CRTs from Tek and HP scopes. we'd like to be rid of all of them (we'd REALLY like the space back), so make any reasonable offer, and they are yours. There all all kinds of *time code units* (displays, converters and generators), including two big 4 foot time displays. there are also some EMI test receivers, and new combined GPS/Leosat positioning systems. Lots of fluke, hp, boonton, GR, pmi/wavetek,Tektronix and other stuff will go, and yes, we take requests if you need something in particular! let me know off list if any interest or questions, all the best, walter (walter2 -at- sphere.bc.ca) sphere research corp. -- Walter Shawlee 2, President Sphere Research Corporation 3394 Sunnyside Rd., West Kelowna, BC V1Z 2V4 CANADA Phone: (250) 769-1834 walt...@sphere.bc.ca WS2: We're all in one boat, no matter how it looks to you ___ 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.
Re: [time-nuts] Lucent RFTG-m-XO failure to obtain GPS signal
b...@iaxs.net said: Have computers but no S/W. Is there a way to tell what's going on without hacking it from the basic bits? Would really like to solve this problem. If it's anything like the other Lucent/HP boxes, the serial port talks ASCII. You should be able to talk to it with a terminal emulator program or direct from the shell. What OS are you using? I can't help with Windows. With *ix, I'd do cat /dev/ttyXX on one window and echo xxx /dev/ttyXX on another. Use stty to adjust baud rate. Was it ever working in your location? Was it ever working in some other location? My quick guess would be that it did a survey at another location and is having trouble getting started because it knows the wrong location. If so, once you can talk to it you can tell it to do a survey... -- These are my opinions. I hate spam. ___ 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.
Re: [time-nuts] Greenwich Timekeeping
The public exhibition for this conference Ships, Clocks and Stars: The Quest for Longitude is apparently coming to the colonies (Canada Australia) this year, so us colonials might get a chance to feast on the Harrison timepieces in all their glory. True clock p**n. Tom Harris celephi...@gmail.com On 26 March 2015 at 03:27, Tom Van Baak t...@leapsecond.com wrote: For those of you near London with an interest in Greenwich, Harrison, and pendulum clocks there's an event on April 18 that might be worth your time. Harrison Decoded: Towards a Perfect Pendulum Clock http://www.rmg.co.uk/whats-on/events/harrison-decoded http://www.rmg.co.uk/sites/default/files/harrison_decoded_draft_programme_250215-3.pdf /tvb ___ 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. ___ 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.
