Re: [time-nuts] GPSDO - probably a stupid question.

Bob wrote: The point is still looking at the noise characteristics of the oscillator and the reference. It is best done in the frequency domain as phase noise. We substitute ADEV, but that is not an ideal proxy. Phase noise and xDEV measure the same thing -- the stability of an oscillator

Re: [time-nuts] GPSDO - probably a stupid question.

I use the frequency relationship ratio as an indication of how difficult the design is. Divide the oscillator frequency with the comparator frequency, and the number gives you a ratio, how many output cycles it goes between each comparison. Things like smoothing becomes harder when this number

Re: [time-nuts] GPSDO - probably a stupid question.

Hi A mixer style phase detector running a GHz range oscillator is one example of a system that technically updated the EFC several billion times a second. There does not have to be a DAC involved. The point is still looking at the noise characteristics of the oscillator and the reference.

Re: [time-nuts] GPSDO - probably a stupid question.

There are no (rarely maybe ) stupid questions, mostly silly answers In a message dated 8/17/2016 5:03:07 P.M. Eastern Daylight Time, elfchief-timen...@lupine.org writes: Wouldn't you also not be able to actually sync to the individual chips, since you can't really see the start of any

Re: [time-nuts] GPSDO - probably a stupid question.

Hi, I agree. There is however a subtle detail, how they leak out over time. At one time we had to lock an 155,52 MHz oscillator up to 8 kHz, this for a 2,48832 Gb/s link, which needs to pass the SDH STM-16 jitter and wander specifications. The first attempt at that PLL was using a 4046, and

Re: [time-nuts] GPSDO - probably a stupid question.

Interested to know if anyone has done this with a ublox receiver, I spotted the option in some of the technical documents and went as far as finding a stockist for the external DAC I think it'd need. On 17 Aug 2016 22:02, "Mark Sims" wrote: > The Ublox modules (at least

Re: [time-nuts] GPSDO - probably a stupid question.

Well, on a practical level, if you update the EFC that frequently then the DAC change glitches will dominate the actual output even if you’re not actually moving the needle much. > On Aug 17, 2016, at 2:53 PM, Bob kb8tq wrote: > > Hi > > You can update the EFC a billion

Re: [time-nuts] GPSDO - probably a stupid question.

Hi You can update the EFC a billion times a second. Update rate and bandwidth are not the same thing. If you want good ADEV, the loop better not have a bandwidth greater than 0.01 Hz. GPS ADEV is pretty awful at 1 and 10 seconds. It is starts to be good past a few thousand seconds. Yes, older

[time-nuts] GPSDO - probably a stupid question.

The Ublox modules (at least some of them) can support an external oscillator and have messages for controlling oscillator parameters and disciplining. > This is actually done. But you need to design the GPS receiver from the ground up to use a very high quality

Re: [time-nuts] GPSDO - probably a stupid question.

In fact, you do not want to "update the crystal one million times/second". The whole point of a GPSDO is to combine the excellent short term stability of the crystal with the excellent long term stability of the GPS signal. If you update the crystal in real time from the GPS data, you do not need

Re: [time-nuts] GPSDO - probably a stupid question.

You can get crystal oscillators that have a frequency control signal and are more stable than the run of the mill oscillators. Changing the GPS oscillator would require modifying a very tightly populated circuit board. Perhaps not possible. What about some of the SDR (software defined

Re: [time-nuts] GPSDO - probably a stupid question.

On Tue, Aug 16, 2016 at 6:02 PM, Peter Reilley wrote: > As a neophyte, I was wondering: rather that trying to discipline an > external > oscillator to create a GPSDO and produce a precise 10 MHz why not > discipline the oscillator > of the GPS receiver itself? > > This

Re: [time-nuts] GPSDO - probably a stupid question.

Some (all?) Novatel receivers have an option to sync their internal TCXO or let it freewheel. -- Björn > The stability of the typical GPS receiver oscillator is usually inadequate > to be useful as a GPSDO. An OCXO (as in the Trimble Thunderbolt for > example) or equivalent is usually

Re: [time-nuts] GPSDO - probably a stupid question.

The stability of the typical GPS receiver oscillator is usually inadequate to be useful as a GPSDO. An OCXO (as in the Trimble Thunderbolt for example) or equivalent is usually required. One can't usually just add a varicap to adjust the frequency of a packaged oscillator. If an external

Re: [time-nuts] GPSDO - probably a stupid question.

On Aug 17, 2016 09:04, "Peter Reilley" wrote: > > As a neophyte, I was wondering: rather that trying to discipline an external > oscillator to create a GPSDO and produce a precise 10 MHz why not discipline the oscillator > of the GPS receiver itself? This could be done

[time-nuts] GPSDO - probably a stupid question.

As a neophyte, I was wondering: rather that trying to discipline an external oscillator to create a GPSDO and produce a precise 10 MHz why not discipline the oscillator of the GPS receiver itself? This could be done with a varactor diode across crystal of the receiver's oscillator. Of