Re: [time-nuts] Adafruit Ultimate GPS timing message arrival times

I’ve used the PA6H so far for all of my GPSDOs. The two reasons I am considering the Venus838LPx-T to replace it are that it has a sawtooth correction message and it has a survey and static solution mode to allow it to tolerate poorer reception. I’m driven to want to experiment with a static mo

Re: [time-nuts] Commercial software defined radio for clockmetrology

> SDRs sample at high rates. The slowest the USRP N2x0 can sample is just under > 200Ksps. Hi Kevin, I don't have an easy answer for you. BobC / BruceG / MagnusD / JohnM / EnricoR can shed light on this. But I support your effort to figure out how to obtain real truth from a massive oversample

Re: [time-nuts] Adafruit Ultimate GPS timing message arrival times

hol...@hotmail.com said: > A couple of people have asked about the poor message arrival time > performance of the popular Adafruit Ultimate GPS receiver. I modified > Lady Heather to analyze the message arrival times using a histogram > instead of a simple average. When I looked at the histogra

Re: [time-nuts] Very Accurate Delta Time RF Pulse

You might be better off scanning than wide band. Even with a slow scanner you can cover the entire RF range every few meters of car travel. But I would sample as fast as you can. Hundreds of millions per second. This gives best sensitivity and noise Use gnu radio software and Their SDR radio

Re: [time-nuts] Adafruit Ultimate GPS timing message arrival times

t...@leapsecond.com said: > Just in case we have some newcomers to the thread I'd like to point out > that this recent series of measurements of RS232 / NMEA have no bearing at > all on the quality of the timing output. Timing NMEA is more of a > curiosity; something to measure at the hundreds or

Re: [time-nuts] Q/noise of Earth as an oscillator

Thanks Tom, I would agree LIGOs efforts are beyond heroic, I will try to find some of their phase noise plots. Regarding Q of the earth, I would agree one could compute an UNloaded Q for the earth as if it were a mass element in some form of a mechanical oscillator. The first sticky point is which

[time-nuts] Trimble Resolution-T GPS timing message arrival times

Attached is a plot of the timing message arrival times of the Trimble Resolution-T receiver running in TSIP mode. Like the Adafruit Ultimate, its firmware seems to do little to get the timing message out at a fixed reference point. As Tom pointed out, this is only an issue if you are trying

Re: [time-nuts] Adafruit Ultimate GPS timing message arrival times

I liked the Adafruit too when I was using it a couple of years ago, but it did have a bad habit of going walkabout.  Yeah, a lot of that was my antenna, but it's still worth mentioning. Bob - AE6RV.com GFS GPSDO list: groups.yahoo.c

Re: [time-nuts] Adafruit Ultimate GPS timing message arrival times

Hi Brooke, That's a reasonable assumption. I haven't ever tried mine at 10 Hz. But note that fast update rates is more meant for navigation and positioning than it is for timing. Just in case we have some newcomers to the thread I'd like to point out that this recent series of measurements of

[time-nuts] Adafruit Ultimate GPS timing message arrival times

It is only tracking the GPS sats, running at 1Hz rate. Almost every GPS receiver that can run faster than 1Hz has warnings that the 1PPS output is only valid/stable if the device is configured for 1Hz output. My Ublox 8 receiver tracks GPS/Glonass/Beidou/SBAS sats. I have seen it trackin

Re: [time-nuts] Adafruit Ultimate GPS timing message arrival times

Hi Mark: Isn't this the receiver that hears a very large number of GNSS satellites and also has a 10 Hz update rate? If so, I'd expect that there would a large variation in message lengths. How stable is the 10 PPS or 1 PPS output? -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.

[time-nuts] Adafruit Ultimate GPS timing message arrival times

A couple of people have asked about the poor message arrival time performance of the popular Adafruit Ultimate GPS receiver. I modified Lady Heather to analyze the message arrival times using a histogram instead of a simple average. When I looked at the histogram data (.01 msec resolution), I

Re: [time-nuts] Commercial software defined radio for clock metrology

Hi There are a *lot* of papers out there on downsampling and ADEV. Just about any / every technique known has been tried and evaluated. The only “correct” answer is to throw away the samples (decimation). Anything else you do will give you subtle (or not so subtle) issues. That said, there ar

Re: [time-nuts] Commercial software defined radio for clock metrology

Hi The simple answer is a filter at the highest sample rate (say 1 second) that impacts the 1 second data. You then decimate from there. If you want 1 second data that “looks right” you start at something higher (say 0.1 second) and filter there. The data set is filtered once (if at all) and d

Re: [time-nuts] Very Accurate Delta Time RF Pulse Measurements

Hi Jerome, This may or may not be of any help, but have you considered using several RTL-SDR devices running at the same time?  You'd need to use a common clock, and probably a number of other enhancements.  But, if you could pull it off, you'd have a wideband RDF type of device.  You'd probably

Re: [time-nuts] Very Accurate Delta Time RF Pulse

I have an Optoelectronics 3000A and as far as I know, the only thing distinguishing this capability from any other frequency counter is discrimination on the digital side which filters unstable counts. In practice it operates like an FM receiver where the strongest signal captures the input. If I

Re: [time-nuts] Commercial software defined radio for clock metrology

Hmm, I might have answered my own question: filter to the fast samples to the equivalent noise bandwidth (ENBW) of the lower desired sampling rate and then decimate. > On Jul 29, 2016, at 9:44 PM, Kevin Rosenberg wrote: > > Hi Bob, > > You have a good point. That leads to the question is what

Re: [time-nuts] Very Accurate Delta Time RF Pulse

Hi Jerome: Some time ago a company called Opto Electronics made a frequency counter with a small antenna that would count the frequency of a nearby signal. They call these Near Field Receivers. Some modern scanner radios incorporate some of these ideas. http://www.prc68.com/I/BC125AT.html --