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] 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] 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] 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] 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] 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] 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

Re: [time-nuts] TCVCXO Adjustment

Could you use the "pips" instead of a PPS signal, again comparing them some weeks apart to give a long reference time ? https://en.wikipedia.org/wiki/Greenwich_Time_Signal If your local radio broadcaster doesn't play something like them, they could probably be generated with a web application.

Re: [time-nuts] TCVCXO Adjustment

wayne.hol...@gmail.com said: > I believe that the "precision" of -20 value on the 4th line is supposed to > be interpreted as 2^-20 seconds which, if my math is correct, works out to > be a precision of about 1 PPM. Is that correct? That's the time between ticks or the time it takes to read the

Re: [time-nuts] TCVCXO Adjustment

Hi With NTP (or any other timing system) you really need 3 or more sources to sort things out. If you only have one source, eventually everything will converge on it. That’s not to say that it will be correct, you simply will be 100% locked to it. GPS modules are a “sub $20” sort of thing

Re: [time-nuts] TCVCXO Adjustment

Again, thanks for all the great feedback and suggestions. > Are you familiar with these devices which I just found this week? > https://tentaclesync.com/products Yes, that's one of the lower cost commercial units available. Another is the NanoLockiIt by Ambient

Re: [time-nuts] TCVCXO Adjustment

Hi If you have a GPS on your local lan, just use it for the calibration. There’s no need for NTP to get involved. If you are running NTP over a normal home setup going to the internet, then you will be doing very well to get low ms with NTP. Going back to the original post, the request is

Re: [time-nuts] TCVCXO Adjustment

Hi NTP will give you “millisecond" level accuracy / stability. If you want to set an oscillator to 0.1 ppm, you will need to run for over 10,000 seconds. It is not uncommon to have things out in the 10 ms range. That would put you at 100,000 seconds. In more common units, a couple of hours to

Re: [time-nuts] TCVCXO Adjustment

Hi Wayne, I didn't mean that you should use the PPS signal from a consumer GPS rx (though you might do that). I was thinking that you'd instead track the difference between TCXO-maintained time and GPS time over long periods - weeks or months - and use those to adjust the TCXO. This would only

Re: [time-nuts] TCVCXO Adjustment

Hi NTP will give you “millisecond" level accuracy / stability. If you want to set an oscillator to 0.1 ppm, you will need to run for over 10,000 seconds. It is not uncommon to have things out in the 10 ms range. That would put you at 100,000 seconds. In more common units, a couple of hours to

Re: [time-nuts] TCVCXO Adjustment

First, thanks for all the comments and suggestions, It's given me a lot to think about and research. Based on the feedback I've received, I've started to investigate using the NTP server approach suggested by Chris Caudle. I also found this NIST Paper

Re: [time-nuts] TCVCXO Adjustment

Why not put a GPS receiver in it ? It won't always get a lock, but if it gets accurate time every few weeks it can do the long-term tweaking someone suggested in the watch thread (call in to the watch repair two weeks apart). Except it can be done more or less EVERY two weeks. I agree, a phone

Re: [time-nuts] TCVCXO Adjustment

On Tue, April 10, 2018 8:12 pm, Bob kb8tq wrote: > Since your typical PC does not have anything in it that is accurate to 0.1 > ppm, you still need something as a reference to compare things to. > A GPS module or a GPSDO are probably the easiest things to get ahold of. Catching up on some of the

Re: [time-nuts] TCVCXO Adjustment

On Tue, April 10, 2018 6:10 pm, Wayne Holder wrote: > which is spec'd at a frequency tolerance or +/- 1 PPM and a frequency > stability of 0.28 PPM and a yearly aging of +/- 1 PPM max/year which, to > me, seems pretty impressive for a part that costs about $8. Something like this MEMS oscillator

Re: [time-nuts] TCVCXO Adjustment

Hi On a TCXO a proper 12 bit DAC should do fine. The “don’t use for DC” DAC’s that are built in to a MCU …. who knows. At DC they probably aren’t 12 bits anyway. If the TCXO is rated to age < 1 ppm per year and has a 10 ppm EFC (yes you *could* wonder about that combo) the DAC would need to

Re: [time-nuts] TCVCXO Adjustment

wayne.hol...@gmail.com said: > Since the TCVCXO includes a voltage control input, my plan is to also add a > 12-Bit Digital-to-Analog Converter ... What's the temperature stability of the D/A? How does that compare with a 10 turn pot? I remember a comment about pots aging. It was somewhat

Re: [time-nuts] TCVCXO Adjustment

If it's just to set for the initial setup or aging, just do it the old-fashioned way, with a trimmer pot to run the Vt - simple, easy to program, and it remembers the setting. Ed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to

Re: [time-nuts] TCVCXO Adjustment

Hi In a commercial setting calibration would be done against a local standard. It might be checked with a counter. It also might be checked against something more complex. A reasonable level of calibration would be 0.1 ppm. Anything much more accurate than that would be quickly swamped by the