[time-nuts] (OT) Frequency and duration of roll out
Alternatively, if you unroll the TP by attaching a stone to the end and letting it drop over a cliff then you have a really interesting physics problem considering the acceleration of gravity, varying mass, inertia, and radius of the roll, nonlinear friction in both air and roller, etc. I remember that, when I was a trainee, we (the engineering trainees) spent some time learning some of the skills that the people that would be working for us had to master. One such was jointing 3 phase cables together. If you wanted to cheese off the instructor, you went to the roll of thin cotton tape, hanging on a roll on the wall, and pulled hard. The weight of the tape coming off the roll was enough to spin the disk, thus bringing more tape off, which was heavy enough to spin the roll some more, so more tape came off, and so on. Thinking back, I don't remember timing the spin rate, more like nipping back to our places so as to be able to deny having carried out the act. :-) Dave (G0DJA) ___ 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] (OT) Frequency and duration of roll out
In message 49a11470.6060...@tiscali.co.uk, Dave Ackrill writes: If you wanted to cheese off the instructor, you went to the roll of thin cotton tape, hanging on a roll on the wall, and pulled hard. The weight of the tape coming off the roll was enough to spin the disk, thus bringing more tape off, which was heavy enough to spin the roll some more, so more tape came off, and so on. This was a well know issue when manipulating the roll while splicing audiotapes. The funny thing was, 2 tapes are really strong. We tied an old studio worktape to the trailer-hook of a friends car when he got married. The tape unrolled flawlessly, the roll clattered wonderfully on the cobbles, and when they turned out of the drive-way it snagged a lamppost and brought the car to a halt until the groom went out and cut the tape :-) -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | 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 To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Different Thunderbolt versions
Thanks everyone for all the input. I actually want to work at frequencies below 50Mhz where a 50 degree phase error corresponds to about 3ns. So for 100 seconds integration time an ADEV of 1E-11 or better at tau = 1s should be fine. I want to keep the system as simple and cheap as possible which is why I want to give the Thunderbolt a try. Also at these low frequencies the required accuracy approaches that claimed by some GPS receivers (4ns for the M12+ ?) so might it be possible to build a system which is accurate for arbitrary integration times? Markus On 22.02.2009, 02:20 Bruce Griffiths bruce.griffi...@xtra.co.nz wrote: Tom Van Baak wrote: For observations at 1420MHz, and short integration times (~ 100sec) the phase error needs to be 100ps or less. For longer integration times (10,000 sec is desirable) and higher frequencies the timing constraints are far more stringent. Whilst clock modeling can be used to improve performance it can only correct systematic effects. Bruce, Approximately what range of tau and ADEV(tau) would this VLBI requirement correspond to? A couple of the TBolts I've tested are at or just under 1e-12 at 1 second and stay almost flat out to 100 or even 1000 seconds. /tvb Tom Really should use something like TDEV but roughly (within a factor of 2 or so at 1420MHz): ADEV 1E-10 or better @ tau = 1sec for 1 second integration time. (integration time to short for anything but very bright objects) ADEV 1E-11 or better @ tau = 1sec for 10 second integration time. (integration time to short for anything but very bright objects) ADEV 1E-12 or better @ tau = 1sec for 100 second integration time. (integration time somewhat marginal for most objects) ADEV 1E-13 or better @ tau = 1sec for 1000 second integration time. ADEV 1E-14 or better @ tau = 1sec for 10,000 second integration time. Also need to take into account that a similar LO would presumably be used at each antenna. For integration times of up to a few hundred seconds VLBI has been done with a hydrogen maser at one antenna and a PRS10A at the other. However the performance isnt Earth shattering and there are some issues with long term drift and transport induced frequency shifts of the PRS10A. For very short integration periods a good OCXO is adequate (at 1420MHz). When an integration time of 1000sec or more is required the LO requirents are more stringent. Bruce ___ 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] (OT) Frequency and duration of roll out
In message: 11721.1235293...@critter.freebsd.dk Poul-Henning Kamp p...@phk.freebsd.dk writes: : In message 49a11470.6060...@tiscali.co.uk, Dave Ackrill writes: : : If you wanted to cheese off the instructor, you went to the roll of thin : cotton tape, hanging on a roll on the wall, and pulled hard. The weight : of the tape coming off the roll was enough to spin the disk, thus : bringing more tape off, which was heavy enough to spin the roll some : more, so more tape came off, and so on. : : This was a well know issue when manipulating the roll while splicing : audiotapes. : : The funny thing was, 2 tapes are really strong. : : We tied an old studio worktape to the trailer-hook of a friends car : when he got married. The tape unrolled flawlessly, the roll : clattered wonderfully on the cobbles, and when they turned out of : the drive-way it snagged a lamppost and brought the car to a halt : until the groom went out and cut the tape :-) Try doing that with CDs :-) Warner ___ 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] Different Thunderbolt versions
I actually want to work at frequencies below 50Mhz where a 50 degree phase error corresponds to about 3ns. What is interesting to listen to below 50 MHz? Are there any handy strong signals you can use for debugging/calibration? Also at these low frequencies the required accuracy approaches that claimed by some GPS receivers (4ns for the M12+ ?) so might it be possible to build a system which is accurate for arbitrary integration times? If you haven't seen it yet, this is wonderful background: http://www.gpstime.com/files/PTTI/PTTI_2006.pdf In particular, be sure to check out the hanging bridges. How far apart are your antennas? Things might get a lot simpler if you can see the same GPS satellites. If your runs are short enough, you might get better results by letting the oscillator coast during the run. That is unplug the antennas or turn the feedback off in software. This could be all wrong There are two things you need. One is frequency, the other is time (PPS). If the time is slightly off, that's equivalent to pointing your antenna in a different direction. You get the same sort of error if the location of an antenna is slightly off. I think the Earth's rotation introduces an error that's equivalent to the frequency being slightly off. -- These are my opinions, not necessarily my employer's. 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] Different Thunderbolt versions
There are two things you need. One is frequency, the other is time (PPS). If the time is slightly off, that's equivalent to pointing your antenna in a different direction. You get the same sort of error if the location of an antenna is slightly off. I think the Earth's rotation introduces an error that's equivalent to the frequency being slightly off. There is two effects... the two antennas will experience different doppler shifts (assuming object in the sky), which can be canceled out fairly easy. There is also the Sagnac effect which causes an apparent time difference, which also can be canceled out fairly easy. Cheers, Magnus ___ 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] Different Thunderbolt versions
Markus Even with sawtooth correction the performance of the M12+T was found inadequate for the LOFAR http://www.lofar.org/p/systems.htm array. They use SRS FS725 rubidium sources disciplined by M12+T GPS timing receivers. They also state that the ionosphere contribution to ADEV is about 8E-12 @10s. Bruce Markus Kern wrote: Thanks everyone for all the input. I actually want to work at frequencies below 50Mhz where a 50 degree phase error corresponds to about 3ns. So for 100 seconds integration time an ADEV of 1E-11 or better at tau = 1s should be fine. I want to keep the system as simple and cheap as possible which is why I want to give the Thunderbolt a try. Also at these low frequencies the required accuracy approaches that claimed by some GPS receivers (4ns for the M12+ ?) so might it be possible to build a system which is accurate for arbitrary integration times? Markus On 22.02.2009, 02:20 Bruce Griffiths bruce.griffi...@xtra.co.nz wrote: Tom Van Baak wrote: For observations at 1420MHz, and short integration times (~ 100sec) the phase error needs to be 100ps or less. For longer integration times (10,000 sec is desirable) and higher frequencies the timing constraints are far more stringent. Whilst clock modeling can be used to improve performance it can only correct systematic effects. Bruce, Approximately what range of tau and ADEV(tau) would this VLBI requirement correspond to? A couple of the TBolts I've tested are at or just under 1e-12 at 1 second and stay almost flat out to 100 or even 1000 seconds. /tvb Tom Really should use something like TDEV but roughly (within a factor of 2 or so at 1420MHz): ADEV 1E-10 or better @ tau = 1sec for 1 second integration time. (integration time to short for anything but very bright objects) ADEV 1E-11 or better @ tau = 1sec for 10 second integration time. (integration time to short for anything but very bright objects) ADEV 1E-12 or better @ tau = 1sec for 100 second integration time. (integration time somewhat marginal for most objects) ADEV 1E-13 or better @ tau = 1sec for 1000 second integration time. ADEV 1E-14 or better @ tau = 1sec for 10,000 second integration time. Also need to take into account that a similar LO would presumably be used at each antenna. For integration times of up to a few hundred seconds VLBI has been done with a hydrogen maser at one antenna and a PRS10A at the other. However the performance isnt Earth shattering and there are some issues with long term drift and transport induced frequency shifts of the PRS10A. For very short integration periods a good OCXO is adequate (at 1420MHz). When an integration time of 1000sec or more is required the LO requirents are more stringent. Bruce ___ 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.
Re: [time-nuts] Lady Heather question serial error
oh yes please!!! dave On Sat, Feb 21, 2009 at 9:21 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: David C. Partridge skrev: Yes, Windows always seems to think a Thunderbolt is an MS mouse. Look back in the archives about using /Fastdetect in boot.ini (BTW this doesn't work with WinXP 64 - so I had to disable the serial mouse in the devices). The cure for that is very old - don't have the serial port connected during windows booting. It happend to me too, but recalling the old workaround and I had no problem what so ever. I'm considering a Linux port since I want to reduce my dependency on Windows at all times. Cheers, Magnus ___ 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. -- Dave Mallery, K5EN (ubuntu linux 8.10) PO Box 3519; T or C, NM 87901 no gates... no windows! free at last! linux counter #64628 (since 1997) People aren't as dumb as Microsoft needs them to be. --PJ, May 2007 ___ 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] Different Thunderbolt versions, group buy
LMAO @ the new TP discussion Thanks for the description of the TBolt buy. Yes, please add my name to the list of buyers for one of the next batch of T_Bolts. I've been putting off buying one to the Ebay offerings, but this opportunity will push me over the edge. I'll definitely buy one. Power supplies aren't a problem for me... I have a few linears that should work well, or I could build whatever I need. If finding a reliable PSU becomes a problem, I can take the T-Bolt without a PSU. Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes. -- Message: 1 Date: Sat, 21 Feb 2009 18:51:38 -0800 From: Tom Van Baak t...@leapsecond.com Subject: Re: [time-nuts] Different Thunderbolt versions, group buy To: Discussion of precise time and frequency measurement time-nuts@febo.com Message-ID: dd4cec4546ac4474804486edcb031...@pc52 Content-Type: text/plain; format=flowed; charset=Windows-1252; reply-type=original I currently have an HP Z3801A, which seems to be running well. I've been looking at the T-Bolts on Ebay for a while, but have been holding off buying. This post just gave me an opportunity to ask some questions. I've seen references to the TAPR group buy in previous posts. It obviously happened before I found this group, but am interested in the details. Things like: When did the buy happen? Which model T-Bolt was bought? What was the price? Was PSU included? Are any units still available? Is another buy planned for the near future? Thanks for the info. Hi Dave, Yes, there have been 3 or 4 large batches of TBolts sold through TAPR over the past year or two. The price ranged from about 95 to 125. Most were sold with power supply; some without (when the source of cheap switching supplies ran out). For more info see: http://www.leapsecond.com/tbolt-faq.htm http://www.leapsecond.com/pages/tapr-tbolt/ http://www.leapsecond.com/pages/tbolt/noise.htm Yes, there will be another group buy or two. However, this time I'm testing all of them first and then announcing the sale (expect mid-March) so that no one has that long wait between ordering and paying/receiving. So hang on a bit longer and I'll send the details next month. Note a number of people have asked privately (you know who you are) and those requests will be handled first. ___ 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.
