Re: [time-nuts] Quantum Time Dilation
A reasonably simple description of this paper was released by Scientific American today: Quantum Time Twist Offers a Way to Create Schrödinger’s Clock https://www.scientificamerican.com/article/quantum-time-twist-offers-a-way-to-create-schroedingers-clock/ The Schrödinger’s Cat thought experiment imagined placing an object in a quantum superposition of two states (cat is alive / cat is dead). The object exists in a superposition of those two states until it is "observed" or measured. This can be thought of as a repudiation of something we assume to be part of our reality -- counterfactual definiteness. https://en.wikipedia.org/wiki/Counterfactual_definiteness You can also imagine putting an object into a superposition of two proper times. https://en.wikipedia.org/wiki/Proper_time The main topic of the Nature article is placing a clock into into a superposition of different velocities, which results in a superposition of the different time dilations due to special relativity. This would result in a non-classical result when measuring the clock (atom or ion) in an experiment. -- Bill Byrom N5BB On Fri, Oct 23, 2020, at 6:13 AM, John Moran, Scawby Design wrote: > It's been mentioned many times here that Time-Nuts are continually chasing > down the more and more esoteric effects that make their clocks less than > perfectly accurate. I wonder whether any of them have got their clocks to the > state where corrections to quantum effects are now in their sights? > > The paper linked here in Nature Communications explains the upcoming problem - > > https://www.nature.com/articles/s41467-020-18264-4 > > Unfortunately, my mathematical skills are not up to working out the magnitude > of any errors. > > John > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] phase noise webinar from IEEE MTT-S
I just attended this webinar. It focused on oscillator design theory and the results the author had achieved for various specific projects. He discussed in general amplitude limiting to reduce amplitude noise, with the result that we only need to worry about phase noise in most cases. Very little time was spent on atomic clocks - he gave three slides which showed Rubidium resonance lines and vapor cells and a block diagram but there was little else. He discussed flicker noise but didn't get into the physical cause of that phenomenon. He spend a bit of time discussing frequency tweaking using varactor phase shifters. The slide deck was not available for download during the webinar. The webinar is now available after the fact on-demand by using the link given earlier (https://www.naylornetwork.com/mtt-mkt2019/email01.asp?projID=122255) and then scrolling down to the "Notify Me!" button, which takes you to the event lobby page. The green box link at the bottom toggles on/off the Resources window. Click "Webinar Evard York" to download a 3 MB PDF of the slides (for slides per page). -- Bill Byrom N5BB On Thu, Oct 8, 2020, at 9:41 AM, jimlux wrote: > https://www.naylornetwork.com/mtt-mkt2019/email01.asp?projID=122255 > > > There's a registration link at the above page. > > > > Low Phase Noise Signal Generation Utilising Oscillators, Resonators & > Filters and Atomic Clocks > > > Tuesday, October 13, 2020 - 12:00 PM Eastern Daylight Time > > Abstract: > > Oscillators and atomic clocks are used in almost all electronic systems. > They set the timing of operations and clock elements as required. The > phase noise, jitter & stability of these oscillators often sets the > ultimate performance limit. Oscillators requiring low phase noise are > used in communications, control, RADAR and navigation systems and also > as flywheel oscillators for atomic clocks, particle accelerator systems > and Very Long Base Interferometry (VLBI) systems. This talk will > initially discuss the theory and design of a wide variety of oscillators > offering the very best performance. Typically, this is achieved by > splitting the oscillator design into its component parts and developing > new amplifiers, resonators and phase shifters which offer high Q, high > power handling and low thermal and transposed flicker noise. Key > features of oscillators offering the lowest phase noise available will > be shown, for example: a 1.25GHz DRO produces -173dBc/Hz at 10kHz offset > and a noise floor of -186dB and a 10 MHz crystal oscillator shows > -123dBc/Hz at 1Hz and -149 at 10Hz. New compact atomic clocks with > ultra-low phase noise microwave synthesiser chains (with micro Hz > resolution) will also be briefly described to demonstrate how the > long-term stability can be improved. New printed resonators (and thereby > filters) demonstrate Qs exceeding 540 at 5GHz on PCBs and > 80 at 21GHz > on GaAs MMICs. These resonators produce near zero radiation loss and > therefore require no screening. L band 3D printed resonators demonstrate > high Q (> 200) by selecting the standing wave pattern to ensure zero > current through the via-hole and new ultra-compact versions (4mm x 4mm) > have been developed for use inside or underneath the package. Alumina > based resonators demonstrating Qs >200,000 at X band have also been > produced. Tuneable versions (1%) have recently been developed. Jeremy > presented the first course on oscillators including a lab class at the > IEEE International Microwave Symposium in Boston in 09. This was > repeated in 2010, 2011. A battery powered lab kit offering 5 experiments > with full theoretical and simulation support was provided. The kit also > produced state-of-the-art performance with flicker noise corners around > 200Hz. The methodology behind this course will be described. Theory and > 5 experiments on the same day was part of the reason for success. The > next generation of oscillators will offer orders of magnitude > improvement in performance. Our current attempts to do this will be > described. > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Spectracom 8161 "Standard Frequency Receiver - Oscillator" for WWVB (and question...)
That's a very old WWVB receiver! * As you can see from that photo, that model was introduced before NIST was created from NBS in 1988 (see the "NBS OUTPUT" BNC). * The "WWVB Continuous Monitored" label appears to be a Tektronix internal calibration sticker. You can see the Tek "bug" logo (CRT side view overlaid with circular display overlaid with Tektronix written at an angle). I worked for Tektronix from 1987 through 2019, and that logo became obsolete about 30 years ago. You can see that the cal sticker is marked "Special Information", and I interpret this as a note that this instrument was used for continuous WWVB monitoring and did not need to be calibrated. * So my guess is that this instrument was originally used at a Tektronix company calibration lab. This could have been at the company headquarters in Beaverton, Oregon, one of the many Tektronix calibration labs located at field offices in the US and Canada (there were two large such labs in Texas in the 1980's), or at one of their worldwide service centers. * As noted by other posters, this model is incompatible with the current WWVB BPSK modulation. See: * https://en.wikipedia.org/wiki/Spectracom#WWVB_changes_affect_early_products * http://maxmcarter.com/rubidium/2012_mod/index.html (search for "8161" on that page for confirmation that these changes work) -- Bill Byrom N5BB On Sun, Oct 4, 2020, at 6:41 PM, Bill Notfaded wrote: > Is this why so many really high end devices are basically dumped on eBay > now? I wondered why SRS device was so cheap now considering price of the > SR620. It's too bad they don't work anymore. I'm sure when this happened > it was a HUGE let down to many here that were using them? What's the best > modern one of these for metrology use? Or has GNSS basically ended it? > I'm very interested in your knowledge about these because I've really > wondered how a modern one would compare to GNSS? > > Thanks, > > Bill > > .ılılı..ılılı. > notfaded1 > > On Sun, Oct 4, 2020, 2:54 PM paul swed wrote: > > > Agree with Bobs comment. The 180 degree phase flip killed all of the gear > > unless significant mods are done or the d-psk-r is used. Great old boxes > > though. > > Regards > > Paul > > WB8TSL > > > > On Sun, Oct 4, 2020 at 3:15 PM Bob kb8tq wrote: > > > > > Hi > > > > > > This is another of the many devices out there that pre-date the > > > “modern” 180 degree phase modulation approach on WWVB. Getting > > > one of these to run properly with the new modulation approach would take > > > some major mods ….. > > > > > > Bob > > > > > > > On Oct 4, 2020, at 10:23 AM, Magnus Danielson > > > wrote: > > > > > > > > Hi, > > > > > > > > I got a bit curious, so I dug up the manual (Available from Orolia that > > > > Spectracom is part of): > > > > > > > > > > > > > https://www.orolia.com/sites/default/files/document-files/8161_manual.pdf > > > > > > > > It is apparent that the reference oscillator is actually free-running > > > > but compared to the WWVB, so you manually tune it to make the > > > > strip-chart become more of a flat line. > > > > > > > > This is interesting, because the receiver locks up another 10 MHz > > > > oscillator. > > > > > > > > Now, there is a 45 degree (2.1 micro) modulation on the WWVB signal, > > > > that shows up as time-tags on the strip-chart, so it is not trivially > > so > > > > that you just replace the simpler 10 MHz oscillator with the more > > > > advanced, unless you can live with that modulation at which time it is > > a > > > > fairlly trivial hack. You can be a bit more cunning to add hardware to > > > > compensate the modulation, but I wonder if that is what is done. > > > > > > > > To figure it out, one has to pop the lid to figure out. That is however > > > > not for me to do. > > > > > > > > Anyway, I thought the manual pointer and quick analysis would maybe be > > > > appreciated. > > > > > > > > Good luck! > > > > > > > > Cheers, > > > > Magnus > > > > > > > > On 2020-10-04 09:37, Kirk Bailey wrote: > > > >> I ran across an interesting widget in my ongoing "find the bottom of > > the > > > >> pile" task. Has a label indicating it was modified for "WWVB > > Continuous > > > >> Monitored"
Re: [time-nuts] IC Used In WWVB Receiver (Link In E-Mail)
I don't have one of those modules. But I believe that most or all such low cost WWVB modules sold on Amazon (and similar distribution sources) use an IC from a Finnish company (Micro Analog Systems). They have produced several different chips over the past 16 years for use in clocks which are synchronized from WWWB and other VLF time signals. They all appear to decode the AM amplitude only (ASK ,but no BPSK demodulation). So they don't provide any frequency or phase information from the signal, and are only meant to provide a demodulated digital stream to a controller which drives a display for date and time display to 1 second resolution. The older modules seem to use the MAS10106B AM receiver IC , which has a single-ended antenna input. The datasheets I can find are dated January, 2004, and this IC seems to be discontinued. The later modules seem to use the MAS6180C AM receiver IC, which has a differential antenna input and so better noise rejection (which can be a big problem for time code receivers). The datasheets I can find are dated September 2014. These are tuned RF receivers and are used with a resonant ferrite antenna and crystal which is resonant at the operating frequency. These IC's work with DCF77 (77.5 kHz), HGB (75 kHz), MSF (60 kHz), WWVB (60 kHz), JJY (40 and 60 kHz), or BPC (68.5 kHz) crystals. The crystals are ground to a 3 Hz higher frequency (except 5 Hz higher for 68.5 kHz). Stray capacitance below 1 pF can affect the crystal resonant frequency. See: https://www.mas-oy.com/portfolio/mas6180c/ https://www.datasheetq.com/datasheet-download/477051/1/MAS-Oy/MAS1016BTB1 -- Bill Byrom N5BB On Mon, Sep 21, 2020, at 7:25 PM, John C. Westmoreland, P.E. wrote: > Hello Time Nuts, > > Does anyone know which IC is used in the following: > (Note: Links have been sanitized by the list moderator.) > > WWVB Receiver on Amazon > <https://www.amazon.com/Alano-Controlled-Modules-Receiver-Operating/dp/B07RYK5KN6> > > It also comes with a clock module: > > With Clock Module > <https://www.amazon.com/ALANO-Controlled-Receiver-Modules-Operating/dp/B07YD2XCFL> > > Thanks In Advance! > > 73's, > John > AJ6BC > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] OCXO retrace, how long is reasonable?
voltage changes by 1 mV as the temperature drops 10C, you might assume that the oven temperature combined with the temperature coefficient of the crystal is causing that change. But the true cause of the measurement change might be the temperature or humidity coefficient of the meter, or placing the low meter test lead on the metal chassis without realizing that the oven current flows through a wire with 10 m ohm resistance to chassis ground, so that a 100 mA increase in oven heater current causes that 1 mV EFC change due only to your improper meter probing. The feedback loop corrects properly even with that ground loop offset, but you can't assume that the EFC voltage change is related to changes in the crystal temperature. Sorry for the long dissertation. I worked at an electronic calibration lab for 4 years, designed some test equipment, and worked as an Application Engineer in test equipment sales for 32 years before retiring late last year. Unfortunately, it's common for users to improperly assume that the reading displayed on the test instrument is the actual precise value of the device under test. -- Bill Byrom N5BB On Sat, Sep 5, 2020, at 2:33 PM, Perry Sandeen via time-nuts wrote: > Learned members, > Wrote: > Well, I could measure the EFC voltage every other day and if it'schanging, > then it's the OCXO that’s drifting, if not (or not inaccordance to the DAC > graph) it's the DAC itself. > > One can buy 5 digit LED meters on ebay for $5 each +shipping. > > While I wouldn't necessarily trust their accuracy, at that price one could > buy 3 or 4 and continuously measure several variables. > Regards, > Perrier > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] "Shaking" of magnetic shields in atomic clocks
Rick, there appears to be interest in "shaking" the magnetic field for both atomic clocks and medical devices which operate at very small magnetic fields (such as magnetoencephalography). Shaking is mentioned here: https://en.wikipedia.org/wiki/Magnetoencephalography#Active_shielding_system I believe that the effect of shaking is to change the average portion of the ferromagnetic material B-H curve the weak external field affects. The incremental permeability (change in magnetic flux density B produced by a small change in magnetizing force H) for a ferromagnetic material is often much larger when the H field is not too close to zero. See this curve: https://upload.wikimedia.org/wikipedia/commons/thumb/3/3a/Permeability_of_ferromagnet_by_Zureks.svg/996px-Permeability_of_ferromagnet_by_Zureks.svg.png The incremental permeability (slope of the B-H curve) is highest at a H field value greater than zero. An AC shaking H field component will allow very weak external fields to interact with the high slope portion of the B-H curve. If the shaking field was not present, the external field would interact only with the low permeability area of the B-H curve (near zero). There is best value for the shaking field which corresponds with the peak in the incremental permeability. The shaking frequency should be much greater than the frequencies of interest to reduce interference. Here are some other references: Design, construction, and performance of a large-volume magnetic shield https://www.researchgate.net/publication/3105787_Design_construction_and_performance_of_a_large-volume_magnetic_shield > The best way to achieve good shielding at low frequencies is to combine > several methods. Ferromagnetic shielding and active compensation are standard > methods for very low frequencies. In ferromagnetic shielding, the walls of a > shield are made of high permeability material, and active shielding uses a > closed loop control system that controls the field within the shield by > special coils driven by a magnetic field sensor. The feedback control system > counterbalances the disturbing field by generating a field equal in magnitude > and opposite in direction to the disturbance. At higher frequencies, it is > possible to use eddy current shielding that takes place when the walls of the > shield form a closed enclosure of high electrical conductivity. > > Still, one method, so-called shaking, can be used in connection with > ferromagnetic shielding. It effectively increases the permeability of a > ferromagnetic material by generating a relatively strong alternating field > into it. However, it generates extra interference at the shaking frequency. Separable Magnetic Shield with Magnetic Shaking Enhancement https://core.ac.uk/display/37850118 Effect of magnetic anisotropy on magnetic shaking https://ui.adsabs.harvard.edu/abs/1999JAP85.4645P/abstract Effective shielding for low-level magnetic fields https://kyushu-u.pure.elsevier.com/en/publications/effective-shielding-for-low-level-magnetic-fields -- Bill Byrom N5BB On Wed, Sep 2, 2020, at 6:32 PM, Joseph Gwinn wrote: > I have not read the paper yet, but this reminds me of the use of AC > bias to linearize the magnetic coating of recording tape. That has the > property of causing linear behavior right through zero average field. > > Joe Gwinn > On Wed, Sep 2, 2020, at 4:31 PM, Richard (Rick) Karlquist wrote: > > In the NIST paper available at the URL below: > > http://pdfs.semanticscholar.org/47ac/742de238c0ece5e91ff7d12c515b9173eb60.pdf > > At the beginning of page 2 (4th line) the paper > states: > > "Note that the shield permeability is a nonlinear function of the > magnetization and increases to a maximum value of umax =400,000 at > higher applied fields. “Shaking” the shields by continuously > applying an alternating magnetic field is a way to take advantage of umax." > ... ... > Rick Karlquist > N6RK > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] China places the final BeiDou navigation system satellite into orbit
IEEE Spectrum article published last week: https://spectrum.ieee.org/tech-talk/aerospace/satellites/final-piece-of-chinas-beidou-navigation-satellite-system-comes-online Space.com published this article on June 23: China launches final Beidou satellite to complete GPS-like navigation system https://www.space.com/china-launches-final-beidou-navigation-satellite.html -- Bill Byrom N5BB ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] eLORAN in the Antipodes ? (was: Re: eLORAN will be on the air GRI 99600)
Yes, the weather can change the phase of the transmitted antenna signal unless corrections are performed. From the WWVB (60 kHz VLF time/frequency station at NIST in Fort Collins, CO) website at https://www.nist.gov/pml/time-and-frequency-division/radio-stations/wwvb (see second paragraph about automatic antenna tuning): > Ideally, an efficient antenna system requires a radiating element that is at > least one-quarter wavelength long. At 60 kHz, this becomes difficult. The > wavelength is 5000 m, so a one-quarter wavelength antenna would be 1250 m > tall, or about 10 times the height of the WWVB antenna towers. As a > compromise, some of the missing length was added horizontally to the top hats > of this vertical dipole, and the downlead of each antenna is terminated at > its own helix house under the top hats. Each helix house contains a large > inductor to cancel the capacitance of the short antenna and a variometer > (variable inductor) to tune the antenna system. Energy is fed from the > transmitters to the helix houses using underground cables housed in two > concrete trenches. Each trench is about 435 m long. > A computer is used to automatically tune the antennas during icy and/or windy > conditions. This automatic tuning provides a dynamic match between the > transmitter and the antenna system. The computer looks for a phase difference > between voltage and current at the transmitter. If one is detected, an error > signal is sent to a 3-phase motor in the helix house that rotates the rotor > inside the variometer. This retunes the antenna and restores the match > between the antenna and transmitter. Changes to the antenna and tuning network affect the transmitted phase, and of course phase changes over time affect the fractional frequency error. At WWVB they control the actual transmitted phase so that it doesn't effect the received frequency accuracy. > The frequency uncertainty of the WWVB signal as transmitted is less than 1 > part in 1012. If the path delay is removed, WWVB can provide UTC with an > uncertainty of about 100 microseconds. -- Bill Byrom N5BB On Sat, Aug 8, 2020, at 3:15 PM, Hal Murray wrote: > > kb...@n1k.org said: > > Same basic issue, lots of weird interactions and a need to keep the signal > > very precise. Not as easy as it might seem. > > What does "precise" mean in that context? > > I'm not an antenna-nut. Can an antenna miss-match change anything other than > the amplitude? > > How do you automatically tune something like that? The manual way would to > twist the knob while watching a meter. If the meter goes down, you are going > the wrong way. If it goes up, keep going until it starts going down, then > back up to the peak you just passed. > > How do you even know that it needs tuning? Can you measure something > accurately enough? If so, what? > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] eLORAN in the Antipodes ? (was: Re: eLORAN will be on the air GRI 99600)
Whit Griffith N5SU was the Chief Radio Scientist (or some similar title) for Continental Electronics in the 1980's in Dallas. In around 1990 Whit gave a slide show presentation to a Dallas Amateur Radio Club meeting at the National Communications Museum, a project at the Dallas Communication Complex in Irving started by Bill Bragg KA5PIP (SK) who became the voice of BIG TEX. Whit showed amazing photos of the VLF transmitter and antenna they had installed in Germany - I believe it was DHO38 at 23.4 kHz. The helix/variometer room was huge, and the antenna used large cables strung between tall towers as a capacitive top hat, and included an impressive ground system. The radiation resistance of a VLF vertical antenna is very low. At 100 kHz one wavelength is 3 km (9,843 feet). So if an antenna was 412 m tall (1,352 feet), it would only be 0.137 wavelength long. The low radiation resistance of such a short antenna requires a high antenna current. At high power levels (1 MW or even more), the antenna current can be several hundreds of amps, and this can produce very high voltages across reactive components of the antenna system and matching network. The result is that high power VLF transmitting stations require a lot of land, a very expensive and large antenna and matching system which retunes itself as the weather changes the antenna impedance, expensive provisions for lightning and high wind protection, an expensive transmitter, and a very high cost for the utility power and maintenance. -- Bill Byrom N5BB On Fri, Aug 7, 2020, at 7:16 PM, Bob kb8tq wrote: > Hi > > Back in the day, if you hung out for a while in the lobby at Continental > Electronics, you would notice a > model of an old style transmitter over by one wall. Go over and look a it for > a a while and all the usual > parts were there. Couple of big tubes, big matching coil insulators here and > there. Eventually you would > notice this tiny spec down by the bottom of the model … hmmm … wonder what > that is? > > Eventually one might figure out that the tiny spec was a person. The model > was of an Omega transmitter …. > > Bob > > > On Aug 7, 2020, at 7:33 PM, jimlux wrote: > > > > On 8/7/20 4:13 PM, Bill Byrom wrote: > >> See this 1961 IRE paper at the NIST website: > >> https://tf.nist.gov/general/pdf/2303.pdf > >> IRE merged with AIEE in 1963 to form IEEE. > >> Figure 7 shows the calculated amplitude transfer of the ground wave signal > >> vs frequency and distance. Note that for 100 kHz signals, the ground wave > >> signal is reasonably strong at 2,000 miles but lousy at 5,000 miles. > >> As this paper notes, the sky wave reflections are delayed, and this delay > >> depends on the ionization state of the ionosphere along the propagation > >> path. This delay is shown in figure 2. > >> Figure 6 shows differences between daytime and nighttime propagation of > >> pulsed signals. The received signal is a combination of the ground wave > >> signal and one or more skywave signals (which are delayed with respect to > >> the ground wave signal). > >> -- > >> Bill Byrom N5BB > > > > and such stuff is why Omega worked at VLF frequencies - none of that pesky > > skywave - lambda=30km and you're ALWAYS below ionospheric cutoff. Alas, > > they made some boneheaded mistakes like making one of the frequencies an > > exact multiple of 60Hz. > > > > There is something positively Tesla-ian about Omega with high power low > > frequency transmitters into physically enormous antennas - like the one > > with the top hat across the fjord. None of this tiny L-band patch antenna > > stuff inside a wristwatch. > > > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] eLORAN in the Antipodes ? (was: Re: eLORAN will be on the air GRI 99600)
See this 1961 IRE paper at the NIST website: https://tf.nist.gov/general/pdf/2303.pdf IRE merged with AIEE in 1963 to form IEEE. Figure 7 shows the calculated amplitude transfer of the ground wave signal vs frequency and distance. Note that for 100 kHz signals, the ground wave signal is reasonably strong at 2,000 miles but lousy at 5,000 miles. As this paper notes, the sky wave reflections are delayed, and this delay depends on the ionization state of the ionosphere along the propagation path. This delay is shown in figure 2. Figure 6 shows differences between daytime and nighttime propagation of pulsed signals. The received signal is a combination of the ground wave signal and one or more skywave signals (which are delayed with respect to the ground wave signal). -- Bill Byrom N5BB On Fri, Aug 7, 2020, at 5:16 PM, Gilles Clement wrote: > Would’nt 100khz carrier propagate mostly by ground wave (during day time) ? > So following earth curvature ? > Gilles. > > > > Le 7 août 2020 à 21:34, paul swed a écrit : > > > > Taka > > Yes it does. More ionosphere than air. It would be skywave or indirect > > path. I mentioned that earlier. > > Now silly thought would a huge antenna work especially if you are at the > > antipode. Further would it be gray line propagation. > > Thats just silly talk. But something to think about. > > Regards > > Paul. > > > >> On Fri, Aug 7, 2020 at 2:01 PM Taka Kamiya via time-nuts < > >> time-nuts@lists.febo.com> wrote: > >> > >> Wouldn't such a long distance propagation result in less precision? The > >> signal will have to go through distance through air which isn't constant in > >> dialectic values. Wouldn't it be problematic for level of accuracy we > >> pursue? > >> > >> --- > >> (Mr.) Taka Kamiya > >> KB4EMF / ex JF2DKG ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Coherent optical clock down-conversion for microwave frequencies with 10^−18 instability
Thanks, Bruce! That's a copy of that same Science article. I guess that NIST got permission to post it on their website, since they were the sponsor of the study. -- Bill N5BB On Thu, Jun 4, 2020, at 6:32 PM, Bruce Griffiths wrote: > https://tf.nist.gov/general/pdf/3093.pdf > is likely more accessible than the sciencemag link > > Bruce > > On 05 June 2020 at 11:15 Bill Byrom wrote: > > > > > > This was published in the 22 May 2020 issue of Science (AAAS journal). For > > AAAS members, the direct link is: > > https://science.sciencemag.org/content/368/6493/889 > > > > They make use of a fiber-based OFC (optical frequency comb) and > > state-of-the-art photodetectors to transfer optical clock stability to a 10 > > GHz microwave signal. This downconversion from optical to microwave was > > done with an error of no more than 10-19 (1 x 10 ^-19). The best available > > optical clock stability is around 10-18 (1 x 10^-18) at a couple of hundred > > seconds averaging time. > > > > This specific experiment compared two independent Yb (Ytterbium) optical > > lattice clocks running at about 259 THz. One Yb clock drove a 208 MHz comb > > generator, while the other Yb clock drove a 156 MHz comb generator. Then: > > 208 MHz x 48th harmonic = 9.984 GHz > > 156 MHz x 64th harmonic = 9.984 GHz > > The phase between these 9.984 GHz signals was compared in a mixer phase > > detector. The fractional frequency instability observed was 10-16 (1 x > > 10^-16) over a 1 second interval. The frequencies I listed above are > > approximate -- they actually measured a 1.5 MHz beat note between the ~10 > > GHz signals. This allowed them to achieve a relative timing error of 900 > > attoseconds (rms). > > > > The optical phase measurements between the two Yb clocks at 259 THz > > indicated a frequency offset (Yb1 - Yb2) of 0.064 Hz, and the microwave > > ~10 GHz comparison was consistent with that offset (2.5 +/- 0.6) x 10-20 > > (10^-20). > > > > The abstract is: > > > Optical atomic clocks are poised to redefine the Système International > > > (SI) second, thanks to stability > > > and accuracy more than 100 times better than the current microwave atomic > > > clock standard. However, > > > the best optical clocks have not seen their performance transferred to > > > the electronic domain, where > > > radar, navigation, communications, and fundamental research rely on less > > > stable microwave sources. > > > By comparing two independent optical-to-electronic signal generators, we > > > demonstrate a 10-gigahertz > > > microwave signal with phase that exactly tracks that of the optical clock > > > phase from which it is derived, > > > yielding an absolute fractional frequency instability of 1 × 10−18 in the > > > electronic domain. Such faithful > > > reproduction of the optical clock phase expands the opportunities for > > > optical clocks both technologically > > > and scientifically for time dissemination, navigation, and long-baseline > > > interferometric imaging. > > > > I have a Science subscription and can read this paper, but I can't > > distribute it here. > > > > You can also see discussion of this achievement by NIST (with assistance by > > the University of Virginia) at Physics World: > > https://physicsworld.com/a/microwave-timing-signals-get-hundredfold-boost-in-stability/ > > > > You may need to request a free account at Physics World to read this > > article. > > > > -- > > Bill Byrom N5BB > > > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] Coherent optical clock down-conversion for microwave frequencies with 10^−18 instability
This was published in the 22 May 2020 issue of Science (AAAS journal). For AAAS members, the direct link is: https://science.sciencemag.org/content/368/6493/889 They make use of a fiber-based OFC (optical frequency comb) and state-of-the-art photodetectors to transfer optical clock stability to a 10 GHz microwave signal. This downconversion from optical to microwave was done with an error of no more than 10-19 (1 x 10 ^-19). The best available optical clock stability is around 10-18 (1 x 10^-18) at a couple of hundred seconds averaging time. This specific experiment compared two independent Yb (Ytterbium) optical lattice clocks running at about 259 THz. One Yb clock drove a 208 MHz comb generator, while the other Yb clock drove a 156 MHz comb generator. Then: 208 MHz x 48th harmonic = 9.984 GHz 156 MHz x 64th harmonic = 9.984 GHz The phase between these 9.984 GHz signals was compared in a mixer phase detector. The fractional frequency instability observed was 10-16 (1 x 10^-16) over a 1 second interval. The frequencies I listed above are approximate -- they actually measured a 1.5 MHz beat note between the ~10 GHz signals. This allowed them to achieve a relative timing error of 900 attoseconds (rms). The optical phase measurements between the two Yb clocks at 259 THz indicated a frequency offset (Yb1 - Yb2) of 0.064 Hz, and the microwave ~10 GHz comparison was consistent with that offset (2.5 +/- 0.6) x 10-20 (10^-20). The abstract is: > Optical atomic clocks are poised to redefine the Système International (SI) > second, thanks to stability > and accuracy more than 100 times better than the current microwave atomic > clock standard. However, > the best optical clocks have not seen their performance transferred to the > electronic domain, where > radar, navigation, communications, and fundamental research rely on less > stable microwave sources. > By comparing two independent optical-to-electronic signal generators, we > demonstrate a 10-gigahertz > microwave signal with phase that exactly tracks that of the optical clock > phase from which it is derived, > yielding an absolute fractional frequency instability of 1 × 10−18 in the > electronic domain. Such faithful > reproduction of the optical clock phase expands the opportunities for optical > clocks both technologically > and scientifically for time dissemination, navigation, and long-baseline > interferometric imaging. I have a Science subscription and can read this paper, but I can't distribute it here. You can also see discussion of this achievement by NIST (with assistance by the University of Virginia) at Physics World: https://physicsworld.com/a/microwave-timing-signals-get-hundredfold-boost-in-stability/ You may need to request a free account at Physics World to read this article. -- Bill Byrom N5BB ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] f-multipliers from VHF to 10 GHz
Wenzel Associates (www.wenzel.com) In Austin TX can build custom rack mounted multiplied very low phase noise crystal sources. I have used their custom microwave multiplied crystal sources at my pre-retirement job (Tektronix RF Application Engineer) with a 12.5 GHz output. A few of my customers also evaluated and purchased these sources for driving the 12.5 GHz external clock input of the Tektronix AWG7A/B series AWG's and 70KSX series oscilloscopes. My experience with this multiplied source was about 2 to 4 years ago, but they probably can still build these. I think the price was roughly US $15,000 for a rack mounted semi-custom system source. One customer purchased the Wenzel golden multiplied 12.5 GHz source to get very low phase noise output of a Tektronix AWG70K AWG to generate microwave chirps for use in electron spin spectroscopy. The AWG70K has an internal moderate performance PLL synthesizer but that wasn't good enough for the spectroscopy experiments. When you use the Wenzel 12.5 GHz external clock, the phase noise of the AWG is dominated by the external clock. There is some small additional phase noise due to the AWG clock edge detection and SiGe DAC wideband noise. Another customer needed to generat very low phase noise RADAR signals. As I remember the Wenzel product block diagram, they used a 10 MHz internal crystal reference oscillator as the master frequency reference with optional EFC electrical frequency control input. A higher frequency very low phase noise VHF crystal oscillator (between 100-200 MHz, I believe) was locked to the 10 MHz internal or external reference, and that VHF oscillator was multiplied and filtered in several stages to get to the microwave range (such as 10 to 12.5 GHz). They could customize their system to provide auxiliary lower frequency outputs from any of the multiplier stages. The Tek AWG70K series arbitrary waveform generators have an external clock input with a range of 6.25-12.5 GHz. The external clock is double clocked on both rising and falling edges. So with a 12.5 GHz sine input, the internal 10-bit SiGe DAC is clocked at 25 GS/s. The AWG70001A and AWG70001B offset two of the 25 GS/s DACs by 180 degrees to get 50 GS/s AWG performance with a sin(x)/x usable bandwidth of nearly 20 GHz. -- Bill Byrom N5BB Retired in Nov 2019 from Tektronix after 32 years as an AE On Thu, May 14, 2020, at 7:58 PM, Gerhard Hoffmann wrote: > I have a potential project in the electron spin spectroscopy sector and > I need > one or two clean signal sources in the 10 GHz range. Phase noise at, > say, 50 Hz offset > is important, but anything below 110 dBc does not care. > That probably calls for a multiplied crystal. These Hittite PLLs from AD > seem to be > just not good enough, maybe they'd work if pushed, but no reserve left. > Are there any known proven multipliers chains from VHF to 10 GHz? > > Cheers, Gerhard > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Using speaker / earphone for PPS testing (not a question)
It's easy to trigger on short pulses on most oscilloscopes if you follow these steps: (1) Do NOT use Auto Trigger mode. Instead use Normal trigger mode. (2) Set the vertical coupling mode to DC. (3) Set the vertical gain (volts/div) and offset so that the baseline (OFF voltage between pulses) and pulse ON voltage should both be visible on the vertical scale. (4) Set the trigger coupling mode to DC and the trigger source to the proper channel. (5) Set the trigger voltage to the midpoint between the pulse OFF and ON voltage. (6) Set the trigger slope appropriately, depending on the polarity of the 1 PPS pulse. (7) Many oscilloscopes have a trigger indicator LED. It should flash visibly on each 1 PPS signal. (8) If you are using an analog scope which does NOT have a microchannel plate (which was used on the Tektronix 2467 family and a few other models), the pulse ON signal may be difficult to see at a fast time/div setting, even with a high scope intensity setting. But you can slow down the time/div of an analog scope to something easy to see, such as 10 ms/div. This will allow you to see a bright sweep each time the scope triggers, even if a short pulse can't be seen. (9) When using a digital oscilloscope, turn on the peak detect display mode. This allows the oscilloscope to keep a high sampling rate even if the time/div is set for a moderately slow sweep. If the 1 PPS signal is very short, you won't be able to hear it on a speaker with a direct connection as you describe. But you can use a pulse stretcher circuit (such as a 555 timer IC) to drive a LED or speaker with a long output pulse (such as 10 ms). If you use two 555 IC's (or a 556 dual timer IC), you can even configure one section as a one-shot and the other as a tone generator so that a beep is produced for each pulse. The 555 and 556 may be sold as LM555/LM556 or NE555/NE556. -- Bill Byrom N5BB Retired Tektronix Application Engineer On Mon, Apr 20, 2020, at 9:25 PM, Taka Kamiya via time-nuts wrote: > Maybe everyone but I knew, but I just did this and found it useful. > 1 pps signal from some GPS are notoriously narrow and difficult to sync > on and see on scopes. LED will barely light if some kind of stretcher > is not used. If your purpose is ONLY to see if it's there or not, hook > up a small speaker, earphone, amplified or not, and you can hear the > tick-tick sound. > > I like DIYing and many times, I wonder if pps distribution circuit is > working. I can tell a very short pulse that will barely register on > LED is clearly audible. > I thought I'd share. > > --- > (Mr.) Taka Kamiya > KB4EMF / ex JF2DKG > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] A Research Proposal
Andy, it appears to me that the FNET/GridEye system already does what you propose: http://fnetpublic.utk.edu The Angle Contour Map displays the kind of results you desire. But it doesn't know the Western Interconnection at this time. I believe there is a typo at the top of the Angle Contour Map: > The frequency gradient map visualizes the real-time angle "differences" with > respect to a referential point in Eastern > Interconnection. Shouldn't that state: "The ANGLE CONTOUR MAP visualizes ..."? According to the legend, the angle contour map displays a measure of the phase angle differences between the individual FDR hosts and a "referential point". I'm not sure if that is an actual specific FDR host or some averaged phase. Of course, you need to think carefully in a relativistic manner when you are trying to look at local phase in locations so far apart. At 60 Hz (in the US) 1 degree of phase corresponds to 46.3 us. That's the free space propagation delay of light over 13.89 km (8.63 miles). Generators 777 miles apart have a 90 degree phase relationship with respect to free space propagation phase. -- Bill Byrom N5BB Irving, TX On Mon, Jul 8, 2019, at 6:11 AM, Andy Backus wrote: > To clarify: > > My research proposal is for data to be taken within the same interconnection. > > It does not care about frequency. > > It does not care about Time Error. > > It only seeks to characterize the phase differences between the power > line signal presented in regions of the distribution system separated > by significant geographical distances. > > 180-degree phase reversals and three-phase transformations along the > chain of information are easily distinguishable. > > Thanks for your interest. I hope some will accept the technical > challenge of gathering data -- which is fairly minimal. > > Andy Backus > Bellingham, WA > (Western Interconnection) > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] timing properties of "spectru spreading" clocks
SSC (spread spectrum clocking) is widely used in both commercial (servers etc.) and consumer products. The big advantage is at harmonics of the spread clock, where the higher frequency energy can more easily escape the product case, shielding, and cables. CISPR (EU) standards in general specify a receiver bandwidth of 120 kHz for signals below 1 GHz and a receiver bandwidth of 1 MHz for signals above 1 GHz. Commonly the SSC clock is generated at 100 MHz with a 1% down-spread at a rate of typically 30-35 kHz. The FM modulation shape is typically a triangle or a “Hershey kiss” shape (think about the profile of those candies). At a 1% spread this means the frequency of the clock is changing between 99 MHz and 100 MHz with a period of roughly 30 us. At the 9th harmonic of the 100 MHz clock, the 900 MHz spurious radiation is spread over a 9 MHz bandwidth. Since the EMI receiver is designed with a 120 kHz measurement bandwidth (to protect commercial broadcast FM reception), the peak power is reduced by a factor (9 MHz) / (120 kHz) = 75, which is 18.75 dB. The SSC clock radiation is then interfering with many more communications channels, but the interference in a narrowband receiver is greatly reduced because the energy is spread over a wide bandwidth. Data transfer based on a clock results in emissions at other frequencies related to the clock frequency and data pattern, and those additional frequencies are spread out similarly when SSC is active. So you have EMI interfering with a large number of communications users, but the standards are based on interference with one channel and indeed the worst-case interference if your receiver happens to be tuned to an exact harmonic of the clock (100 MHz, 300 MHz, 500 MHz, 700 MHz, 900 MHz, etc. since odd harmonics are much stronger for 50% duty cycle square waves) are much reduced from what they would be without use of SSC. The regulatory authorities decades ago might have forced all digital devices to be run at certain narrowband frequencies and created guard bands where radio services were not authorized (such as ISM bands for industrial RF use), but they couldn’t control the clock frequencies of digital devices but only their emissions, so they caused an unfortunate situation where you find EMI spread over a wide range of frequencies with no regard to the users assigned to those specific frequencies, but the standards allow the SSC trick to interfere with even more users but at a lower worst-case level. So if you tune a radio receiver across a wide frequency range, you find EMI at many frequencies but the worst-case peak amplitude is reduced. SSC introduces various types of jitter into the clock. Cycle-to-cycle jitter is often the main issue, and the details of how the frequency modulation is performed can make a big difference. Some techniques use an analog modulated VCO, while others use digital techniques (such as switched delay lines). The frequency and phase are not always smoothly changing and in some parts can be non-monotonic over small time intervals. In some cases the clock generator clocks both the sending and receiving end of a serial or parallel data transfer, and the cycle-to-cycle jitter has to be within a certain limit to prevent setup and hold time receive clocking failures. In other cases the receiving system has a PLL which recovers the clock and following stages don’t see the SSC. Some devices (in particular microprocessors) have very strict clock frequency upper limits, so it’s common to see down-spreading used where the clock frequency is always at or below the datasheet clock maximum frequency specification. Many SSC clock generator chips have detailed specifications of their worst-case cycle-to-cycle jitter. I sell spectrum analyzers, and I commonly use an EMI sniffer probe (or just a 450 MHz rubber duck style antenna) to show SSC clocks in the environment. I will commonly see such signals, which look similar to ATSC digital television or LTE cellular signals in that the spectrum is rectangular (or more accurately trapezoidal with slopes at the edges of the channel). A low-cost USB spectrum analyzer (such as the RSA306B from my company — a warning that I am a biased commentator) can show the spectrum and the frequency vs time waveform. Oscilloscope jitter analysis tools can also display the frequency vs time behavior. As noted above, the modulation frequency is usually between 30 and 35 kHz or so. -- Bill Byrom N5BB Tektronix RF Application Engineer On Sun, May 19, 2019, at 7:41 PM, Poul-Henning Kamp wrote: > > In message <80833925-1229-45a3-18ad-3395793c0...@earthlink.net>, jimlux > writes: > > >Has anyone measured the details of the spread spectrum clocks used to > >help meet emission limits (like FCC Part 15)? > > Most of the ones I've seen just FM modulate with a triangle. > -- > Poul
Re: [time-nuts] injection locking crystal oscillator
In the June 1946 issue of "Proceedings of the I.R.E.", Robert Adler published "A Study of Locking Phenomena in Oscillators*. I believe this is the first full study of injection locking. This paper was so important that it was republished in the October 1973 issue of "Proceedings of the IEEE". This paper give the required condition (under a small signal approximation) for injection synchronization as: (Einj/E) > (2 Q) | delta w / w | (equation 13b) I can't accurately reproduce this equation in plaintext, but it states that the ratio of the injected voltage to natural oscillator voltage must be greater than twice the product of the circuit Q and the absolute value of the fractional frequency error between the injection frequency and natural oscillator frequency. From this equation it would appear that for a large Q (such as 100,000) the lock range of the injection frequency would be much less than +/- 5 ppm, since the injection voltage would normally be much less than the natural oscillator voltage. For lower Q circuits a larger lock range would be available as long as the injection voltage wasn't too weak. Access to the Adler paper from either of the publication dates requires IEEE membership or related credentials, but the principles laid out there are extended in the freely available papers below: ** "A Study of Injection Locking and Pulling in Oscillators" (Behzad Razavi in IEEE Journal of Solid-State Circuits, September 2004) : http://www.seas.ucla.edu/brweb/papers/Journals/RSep04.pdf This paper derives in a different manner "Adler's equation" [ equation (28) in the paper ], which describes the behavior of LC oscillators under injection. This should also be applicable to crystal (and other resonator) oscillators. Section III (Injection Pulling) C (Quasi-lock) describes the behavior when the injection frequency is outside the lock range. Section IV (Requisite Oscillator Nonlinearity) shows that nonlinear behavior in the oscillator is necessary for injection locking to work. Section V (Phase Noise) describes the reduction of the phase noise of an oscillator by a low-noise injection source. Section VI describes the effect of injection pulling on a PLL. ** "Gen-Adler: The Generalized Adler’s Equation for Injection Locking Analysis in Oscillators" (Bhansali and Roychowdhury in IEEE 2009 Asia and South Pacific Design Automation Conference): http://potol.eecs.berkeley.edu/~jr/research/PDFs/2009-01-ASPDAC-Bhansali-Roychowdhury-GenAdler.pdf The second paper listed above uses "Perturbation Projection Vector (PPV)" analysis, which I don't understand. The authors derive a Generalized Adler's equation which is valid for any type of oscillator. Ring oscillators are discussed, and oscillator waveforms are shown when the injection has a sine, square wave, or exponential waveform. I post this in case anyone wants to use an analytical approach to investigating injection locking. -- Bill Byrom N5BB On Fri, Mar 1, 2019, at 9:00 AM, Neil wrote: > I have five systems using injection locking. There are a few issues to > watch. If you inject at too high a level, any noise on the reference > will appear in the oscillator output. I use a 56 ohm resistor to > terminate the reference signal coax input, then a 100pF cap and a series > resistor connected to on leg of the crystal. The resistor value needs > to be selected so I can get a solid pull-in and lock over an > acceptably-wide range. In most cases, I am multiplying the crystal osc > up to 3.3, 5.6 or 10.2 GHz and using a PLL chip driven from an Rb as the > reference to generate 0dBm at the correct locking frequency around 117 > MHz for example. > > If the crystal free-runs close to the lock frequency, say within 200ppb, > the series resistor can be 5k or so, and there is almost no effect on > close-in noise, and no sign of spurs. If I have to pull the crystal > more than about +-500ppb, the resistor needs to be a few hundred ohms, > and the synth noise sidebands start to be seen in the osc output. With > a 70 ohm series resistor, the noise of the osc is only about 10dB down > on the noise of the synth, but the lock-in range is around +-1200 ppb, > slightly more on the LF side. > > When the osc drifts too far away from the reference, or the level is too > low, you get a spread of frequencies out of the oscillator as it tries > to pull into lock, but doesn't make it. As the lock level rises, it > pulls closer in, but still with a spread of frequencies until it finally > jumps into lock. There is considerable hysteresis, so check thoroughly > that it will pull in under all likely conditions of voltage and temperature. > > Remember that the coax lead is going to have a major influence on the > oscillator, so keep it short and watch for
Re: [time-nuts] How can I measure time-delay of a cable with HP 5370B time-interval counter?
Sorry for the delayed response, David. It took me a while to do a bit of research and I have some clues to why you measured those confusing results. Please refer to the HP5370B operation and service manual at the following link. The specifications are on pages 1-3 and 1-4 (pages 12-13 of the PDF). The input amplifier schematic diagram is on part three of page 8-85 fold out (page 256 of the PDF). https://literature.cdn.keysight.com/litweb/pdf/05370-90031.pdf?id=713250 You have the following connections, following the cable from the source to the termination: (1) Sinewave generator: If you want to measure the low frequency characteristics of the cable, you will need to use a sine waveform. If you use a fast risetime pulse or square wave you will measure the characteristics at frequencies related to the risetime of the pulse, not the period or width of the pulse. (2) BNC TEE connector at the Start input of the HP5370B: You have the switches for the Start channel set to 1 M ohm, divide by 1, AC coupling, and rising edge. The input impedance of the Start input is 1 M ohm in parallel with <50 pF, and the BNC TEE adds a few more pF and also a few mm of propagation distance between the center of the Tee and the reference plane at the Start connector. At low frequencies these effects can be safely ignored, but I'm guessing that at 30 MHz you might see an affect if you are measuring with 3 digit resolution. The AC coupling capacitor and 1 Mohm termination produce a highpass RC filter with a corner frequency of about 16 Hz. At 10 MHz this is inconsequential, but at 1 kHz this will cause some noticeable phase errors. (3) BNC termination at the Stop input of the HP5370B: You have the switches for the Stop channel set to 50 ohm, divide by 1, AC coupling, and rising edge. The combination of AC coupling and 50 ohm termination used at low frequencies is one of your main problems. The combination of the 10 nF (0.01 uF) series AC coupling capacitor and 50 ohm termination after that coupling capacitor produces a high pass RC filter with a corner frequency of about 318 kHz. At the corner frequency the Stop input amplifier amplitude is 0.707 of the voltage at the BNC TEE, and at 10 kHz the counter voltage comparator has a very small input swing due to the highpass characteristics. The phase is affected greatly, and at the corner frequency of 318 kHz the counter sees a 45 degree phase error due to the AC coupling highpass filter. That's a 393 time delay error due to the AC coupling at that frequency, and the effect gets worse as the frequency is reduced. Skin effect below 100 MHz: In addition to the methodology (wrong measurement tool and setup), I question the premise behind the test. I believe that the low frequency (below 30 MHz) dielectric properties of common RG-58 and similar coaxial cable are reasonably stable versus frequency. But the skin depth depends on frequency, and this will change the resistance and more importantly the internal inductance of the center conductor. At very low frequencies the AC fields penetrate throughout the center copper wire conductor and this causes internal inductance. As the frequency is increased the skin depth produces a significant reduction in the cross sectional area where conduction can occur, so the inductance is lowered. The crossover frequency where the AC resistance (due to skin effect) equals the DC resistance of a copper conductor depends on the wire diameter as shown in figure 4 of this informal paper: http://www.ve2azx.net/technical/CoaxialCableDelay.pdf Figure 7 in that paper shows a graph of the calculated delay (ns per meter of cable length) of RG-58 coax between 1 MHz and 1 GHz on a logarithmic frequency scale. You can see that the calculated change in the propagation delay is about: 1 MHz: 1.630 ns per meter 10 MHz: 1.573 ns per meter 100 MHz: 1.555 ns per meter 1 GHz: 1.550 ns per meter Are you really distributing low frequency sinewave signals, or pulses with a low repetition frequency? -- Bill Byrom N5BB On Mon, Oct 29, 2018, at 10:25 AM, Dr. David Kirkby wrote: > On Mon, 29 Oct 2018 at 09:43, Tom Van Baak wrote: > > > David, > > > > Just to see if your setup is working: > > > > 1) Set the pulse generator to as fast a risetime as possible; ns or less. > > Use a low pulse rate (100 Hz is fine). > > > > Unfortunately, I don't have such a pulse generator, so I can't run that > test. But it is clear the system is sensitive to the trigger levels, so I > guess is the problem. I have done all the confidence checks in the manual > on this TI counter before and it was fine. > > Also, I am interested in the delay of the cable at low frequencies, as I > suspect that might depart significantly from the usual figure based on the > "velocity factor". Certainly the impedance of coax ris
Re: [time-nuts] A silly question ...
In addition to nonlinear issues with output amplifiers, filters have poor performance when improperly terminated. This can lead to harmonic distortion and that can be a problem. You want the duty cycle to be exactly 50%. See:https://tf.boulder.nist.gov/general/pdf/1437.pdf -- Bill Byrom N5BB On Fri, Sep 28, 2018, at 10:30 AM, Dana Whitlow wrote: > Hi, > > There is one other issue that can bite you if you fail to properly > terminate the output of a source: > > Depending on the source's design, an essentially unloaded output > can have a substantially higher voltage swing than expected (by > 2X if the source impedance is actually 50 ohms), possibly leading > to the output stage's going into clipping, which can in turn distort > the timing, possibly even in an unstable manner. > So if you want to play the "unterminated game", at least take a > look at the waveform to be sure it's still a clean sinewave. I've > noticed such distortion on my PRS-10, for example, although I've > seen no evidence of unstable timing results. But in this arena, > it generally pays to be fussy. > > Dana Whitlow > > On Fri, Sep 28, 2018 at 7:06 AM Bill Byrom > wrote:> >> On Thu, Sep 27, 2018, at 11:55 AM, Dave B via time-nuts wrote: >>> Triggering a dual beam 'scope (Tek 465) from the TB on Ch1, and >>> having>>> the output of the OCXO on Ch2, the resulting display on Ch2 of >> course>>> drifts in relation to the static waveform on Ch1. (Both nice >>> sinusoids.) >> The Tek 465 analog cathode ray oscilloscope was/is a very flexible >> instrument. But this flexibility allows you to set up the >> instrument in>> ways which will not allow this commonly used oscillator >> comparison >> technique to work correctly. Since you are interested in these >> instruments, here are some details about setting up the >> instrument for>> such comparisons. >> (1) The Tek 465 is not a dual beam oscilloscope. Dual beam >> oscilloscopes>> (such as the Tektronix 556 and 7844) use a special CRT >> which >> incorporates two independent electron guns. Each electron gun >> assembly has a set of vertical and horizontal deflection plates. >> There are two vertical amplifiers (one for each electron gun) and >> two horizontal sweep systems (one for each electron gun). If >> you had>> a dual beam oscilloscope you could compare oscillator#1 to >> oscillator#2 while simultaneously comparing oscillator#3 with >> oscillator#4. It's like having two independent oscilloscopes >> sharing>> the same CRT display. >> (2) The Tek 465 single beam oscilloscope can display two traces on >> the>> display using one of two methods:(a) Chopped trace display: >> This mode>> works well at low sweep rates (such >> as 1 ms/div) but causes trouble at fast sweep rates (such as 1 >> us/div). The displayed trace is switched between Channel 1 and >> Channel 2 at a fixed rate of about 500 kHz.(b) Alternate trace >> display: This mode works well at high sweep rates >> but is hard to see at low sweep rates. The scope alternates between>> >> displaying one sweep of Channel 1 and one sweep of Channel 2. >> (3) The trigger source setting is crucial to using this technique to>> >> compare oscillators. The technique does not require you to display>> two >> channels. What is important is that you display one oscillator>> while >> triggering on the other oscillator. The trigger source can >> be set to:(a) CH 1: The Channel 2 display will drift if the two >> signals have a >> varying phase relationship.(b) CH 2: The Channel 1 display will >> drift>> if the two signals have a >> varying phase relationship.(c) NORM (normal): The trigger >> system gets>> input from the channel being >> displayed at that moment. So in chopped trace display mode the >> trigger is rapidly switched between CH1 and CH2, and in alternate >> trace display mode the trigger alternates between CH1 and CH2 on >> alternate sweeps. In all cases, you should not use NORM trigger >> source with both channels displayed when comparing oscillators!(d)>> EXT: >> You apply the trigger signal to the external trigger input >> connector. This works well well when comparing oscillators. If you>> use >> alternate trace display mode and an external trigger, you can >> compare oscillator#1 (on CH 1) to oscillator#0 (on the external >> trigger input) while you are also comparing oscillator#2 (on CH2) >> oscillator#0. So you could compare two oscill
Re: [time-nuts] A silly question ...
ator you are using for the trigger. (6) If the edge rate is not very fast (such as when you are measuring sinewave signals), the waveform edge you see at a fast sweep rate will appear to be nearly horizontal (spread out across many divisions). You normally want to measure the displayed signal at the midpoint of the peak to peak voltage swing. For a sinewave this will be the zero crossing, and for a square wave this will be the 50% point on the edges. You can get better resolution on determining the edge timing by increasing the vertical gain (reducing the volts/div) setting on the oscilloscope. But you probably only want to increase the gain so the signal is off the screen by a factor of 2 to 5, because too much gain may result in overdrive recovery problems in the vertical amplifier. The trigger signal (on a display channel or external trigger input) gain should also be increased to get lower jitter triggering. (7) The Tek 465 input impedance (of CH1, CH2, and the external trigger input) is 1 M ohm in parallel with about 20 pF. If you are using 50 ohm cables, it's best to use 50 ohm feedthrough terminators on the two connectors to which the oscillators are connected. With low frequency (no higher than around 10 MHz) sinewave sources a lack of proper termination doesn't cause many problems, but if a signal has fast edges (small values of risetime/falltime) an improper or missing termination can result in reflections. This can cause distortions in the waveform near the rising and falling edges which add jitter and cause unstable triggering of the scope. So it's good engineering practice to properly terminate the cables at the oscilloscope BNC connectors.-- Bill Byrom N5BB Tektronix Application Engineer for past 31 years. First used the Tek 465 about 42 year ago. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
