Re: [time-nuts] TCVCXO Adjustment

HI > On Apr 14, 2018, at 7:11 PM, Wayne Holder wrote: > >> The application is time stamping separate free running devices, in this >> case different video and audio recorders. So the absolute time is >> arbitrary, but all the devices in use have to agree on the rate of

Re: [time-nuts] TCVCXO Adjustment

> The application is time stamping separate free running devices, in this > case different video and audio recorders. So the absolute time is > arbitrary, but all the devices in use have to agree on the rate of time > progression for as long as they are being used together. > The typical

Re: [time-nuts] TCVCXO Adjustment

Hi It’s reasonable to expect the slope of the EFC to vary 2:1 over it’s range. Could be more, could be less. How much depends a lot on what the original OEM wanted on surplus parts. In the case of “bought new” you would have to check the data sheet. If there’s no spec, it’s reasonable to

Re: [time-nuts] TCVCXO Adjustment

Hi That’s one possible application. Jim’s VLBI in the back yard is another possible application. If this is aimed at “distributed VLBI” then the requirements are … errr … pretty tight. Bob > On Apr 14, 2018, at 4:43 PM, Chris Caudle wrote: > > On Sat, April 14, 2018

Re: [time-nuts] TCVCXO Adjustment

On Sat, April 14, 2018 8:37 am, Bob kb8tq wrote: > big an issue as the TCXO. If it's a single location and the time is > arbitrary, then maybe not so big a deal. > If it's all arbitrary why worry about drift? > > GPS on the board looks like a good thing to have to me The application is time

Re: [time-nuts] TCVCXO Adjustment

kb...@n1k.org said: > The gotcha is that you do not have a calibrated adjustment. Put another way, > there isn’t a perfect correlation between DAC bits and ppm. Each adjustment > you make is subject to a bit of error. When you are trying to get within a > ppm, your measurements are quicker, so

Re: [time-nuts] TCVCXO Adjustment

Hi > On Apr 14, 2018, at 11:10 AM, Adrian Godwin wrote: > > What if you iterated toward a suitable minimum-error setting, then looked > for cyclic corrections with a period of weeks to months. Once you start to > see that, choose the centre of the cycle and track it (or

Re: [time-nuts] femtosecond jitter

Hi, Magnus, We did a little PC board that has two Analog Devices CML comparators that feed the flop.   https://www.dropbox.com/s/05ti1c57eush0uq/99S394A.pdf?dl=0 An external DAC tweaks the VBIAS voltage to slew the edge times across one another, and an external ADC looks at the averaged

[time-nuts] Spectracom Netclock 2 (cannot enter date time manually)

I know this should be as simple as reading the manual however... I am using Tera Term with a PC laptop connected from serial port to serial port: VT100 9600 Baud Data: 8 bit Parity: None Stop: 1 bit Flow control: none The cable is a DB9 to DB9 "Straight Through" Serial Cable of

Re: [time-nuts] TCVCXO Adjustment

What if you iterated toward a suitable minimum-error setting, then looked for cyclic corrections with a period of weeks to months. Once you start to see that, choose the centre of the cycle and track it (or perhaps just increase the time constant). On Sat, Apr 14, 2018 at 2:37 PM, Bob kb8tq

Re: [time-nuts] TCVCXO Adjustment

Hi The gotcha is that you do not have a calibrated adjustment. Put another way, there isn’t a perfect correlation between DAC bits and ppm. Each adjustment you make is subject to a bit of error. When you are trying to get within a ppm, your measurements are quicker, so the larger error (

Re: [time-nuts] femtosecond jitter

On Fri, 13 Apr 2018 08:54:41 -0700 John Larkin wrote: > If you walk the differential data and clock inputs of an NB7V52  CML > flipflop across one another in time, the equivalent jitter is below 20 > fs RMS. That's what we're measuring, but our test rig may

Re: [time-nuts] TCVCXO Adjustment

Hi The uBlox based parts will provide pretty good timing into a directly connected PC. By that I mean, they are on a dedicated USB controller hooked directly to the CPU. In this context, the objective is microsecond level timing. We’re not after a TimeNut couple of nanoseconds. Even if it’s

Re: [time-nuts] femtosecond jitter

John, How where these measurements done? Also, it looks like you have a systematic component in there, about 80 fs guestimating from the plot creating essentially two tracks up the slope that is the tell-tale of a sinuoid phase modulation of some source. Considering the temperature stability

Re: [time-nuts] TCVCXO Adjustment

Hi Yes you could. If you are listening to them by ear, something in the ~100 ms range is probably a good guess in terms of precision. There are also propagation issues that may come in with a broadcast system. If you are still after 0.1 ppm, that gets you out to a million seconds per

Re: [time-nuts] getting accurate timing on RTL-SDR output

Hi Jim, > That's the sort of strategy I'm looking at.. find a set of samples where > the transient occurs, zero pad it out (so that when I do peak picking > later, I've effectively got interpolation), then run the correlation You find it using cross-correlation, and once found, you have a fair

Re: [time-nuts] TCVCXO Adjustment

Wayne, On 04/11/2018 01:10 AM, Wayne Holder wrote: > I'm designing a small, portable, SMPTE LTC Timecode Generator > as an open source/hardware > project for amateur filmmakers and videographers. LTC Timecode is > typically recorded on the audio

Re: [time-nuts] Pulsars, clocks, and time nuts (Jim Palfreyman)

Bill Hawkins writes: > It seems that pulsars are rotating stellar objects that have no reason > to change their rotation, except to decay. The whole point of that exercise was to determine which of the theories that predict what the internal structure of a neutron star looks like is more likely

Re: [time-nuts] getting accurate timing on RTL-SDR output

jimlux writes: >> A maybe not-so obvious approach would be to use RTL-SDR that have been >> modified for direct sampling (usually via the Q branch) and inject your >> timing pulse there. That would limit the disturbance of the actual >> signal while still relatively easy to extract from the data

Re: [time-nuts] TCVCXO Adjustment

If you compare VCXO time with UTC or GPS once a month to an accuracy of 1s (with NMEA or even a time signal and manual pushbutton) and make a correction for the 2.5 million seconds that occurred since the last correction, you'll be better than 0.5 ppm. Is that good enough ? On Sat, Apr 14, 2018

Re: [time-nuts] Pulsars, clocks, and time nuts (Jim Palfreyman)

According to my book, each magnetic pole of some pulsars is more like a rotating circular array of sub-poles, where the direction of induced radiation varies from sub-pole posetion to sub-pole position. And only a small range of sub-pole positions out of the group happens to point in the

Re: [time-nuts] Pulsars, clocks, and time nuts (Jim Palfreyman)

It seems that pulsars are rotating stellar objects that have no reason to change their rotation, except to decay. Ruling out causes from the stellar object, one is left with things that might be orbiting the object and their ability to absorb the pulse that is aimed at us. One could move further

Re: [time-nuts] TCVCXO Adjustment

kb...@n1k.org said: > The alternative is to plug a USB GPS into the mac and do a bit of code to > compare things. If you want to pass the gizmo around to your friends …. that > can be done. Pretty good ones are “sub $10” delivered. USB GPS gizmos generally don't have a PPS and the timing