Re: [time-nuts] I've been thinking about a GPS receiver experiment

Living in south Florida I have been through 8 hurricanes and uncountable thunderstorms, while being a time-nut. At no time a hold over, because of excellent power backup. Once a controlled power shut down in Miami because I had to make a choice between window Air conditioner, refrigerators

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Terrific points. There are so many levels of sophistication. My own experience is with catastrophic signal loss on the reference. Determining degradation on your primary reference can present challenges. I once designed a device that compared three Cesiums and switched the reference within

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Hi You get into all sorts of issues trying to estimate tempco. You have time lags and gradients that make it a very messy process. Toss in measurement based on small range temperature swings (like from a HVAC system) …. it’s a mess. If the OCXO is a typical modern part and it’s been on power

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Hi Most GPSDO’s do some sort of “slew” to an average DAC value when they go into holdover. Freezing at the last value is not (in general) a good idea. Often things degrade before there is a dropout. Your final DAC value may not be a good one to maximize holdover duration. Some setups try to

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Sorry, my mistake, change that to the former! I have used DACs that were monotonic with decent results but prefer analog loops when the time constants are short enough. Bob M On 10/25/2017 5:46 PM, Bob Martin wrote:   The holdover state is a DAC set to the last value of the analog control

Re: [time-nuts] I've been thinking about a GPS receiver experiment

The holdover state is a DAC set to the last value of the analog control voltage that adjusts the oscillator frequency. Some designs use an analog control loop and switch the DAC into the control loop. Others use the DAC to set the control voltage at all times. This can result in a steps in

Re: [time-nuts] I've been thinking about a GPS receiver experiment

What "naughty schoolboy"? How else is one supposed to learn feedback theory? Dana On Wed, Oct 25, 2017 at 6:30 PM, Mark Sims wrote: > > No, you set up an oscillator so that is why you have that problem. > > I hooked the two rubidiums together just to see what would

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Hi naugthy schoolboy Mark, On 10/26/2017 01:30 AM, Mark Sims wrote: No, you set up an oscillator so that is why you have that problem. I hooked the two rubidiums together just to see what would happen. It pretty much did what I expected... chaos... the time-nut equivalent of a naughty

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Hi Bob, Well, the PRC-10 actually have additional provisions to help it do well on GPS as signal, and is used by severals to do exactly that. Cheers, Magnus On 10/25/2017 09:26 PM, Bob kb8tq wrote: Hi Everybody I have ever talked to about the internal disciplining on Rb’s comes up with

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Hei Ole Petter, You don't want to look at the PPS in that case. You want to look at how the receivers clock solution pans out. Since the receivers clock is set but then ticks to the speed of the rubidium, you now got a high resolution frequency and phase comparison. Depending on the

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Hi Mark, On 10/25/2017 12:42 AM, Mark Sims wrote: I did a quick silly experiment where I took a PRS-10 disciplined by an X72 which was disciplined by the PRS-10. The result seemed to have created a rupture in the space-time continuum. Nobody was happy... they didn't seem to agree on who

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Hi Everybody I have ever talked to about the internal disciplining on Rb’s comes up with “it’s not for a GPSDO” somewhere in the first minute of the conversation. The objective seems to be to tune the unit to a perfect source to speed up the calibration process. The idea never appears to

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Hi Since you are doing a loop design that involves “months long” data runs, having good logging and monitoring is a key part of the process. Without the testing side of the process you are pretty much guaranteed to go astray in one way or the other. That’s not to say you have to have a giant

Re: [time-nuts] I've been thinking about a GPS receiver experiment

I did log the #TIME message for several weeks on an OEMV-3 a while back. The results were a bit suspicious, so I checked with Novatel support - turns out the PPS on the OEMV (and I presume that also holds for OEM4) is derived from L1 only - and the jitter is nothing to brag about. So for

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Hi The “best” approach would be to use a receiver that reports what’s going on to some pretty good resolution (say picoseconds). You also measure the pps offset (say to picoseconds). Then you feed *both* numbers into a software loop. Since you are after a loop with a “many days” sort of

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Hello Skip, I have a theory, but it will be interesting to see what others say. Assuming that the 1 PPS error to which you refer is the so-called "sawtooth" error, I've come to suspect that the rate at which the individual PPS pulses walk across the sawtooth is related to, and likely proportional

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Skip, I would rather use the rich Novatel reports and read out the time error and use that as your phase detector, then the normal PI-loop stuff with an optional low-pass to add and then use that to steer the rubidium. It's one of those, when I get time, projects. Cheers, Magnus On