Re: [time-nuts] Some observations of the BG7T BL GPSDO
-Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Stewart Sent: Sunday, March 22, 2015 7:03 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Some observations of the BG7T BL GPSDO Hi John, Doesn't that have a NEO-6M in it rather than a timing receiver? Bob I've (recently) heard that it does. Also, apparently the DOCXO is tuned by a 16-bit DAC that results in steps of about 0.15 mHz. The system is frequency-locked rather than phase locked, so a frequency error of that magnitude is considered normal, according to an email from BG7TBL to Bob R. -- john, KE5FX Miles Design LLC ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Comparing the BeagleBone Black Raspberry Pi as NTP servers
On Sun, 22 Mar 2015 16:41:56 -0400 Paul tic-...@bodosom.net wrote: 1) Did you start out using the attached patch antenna? D Drown implies successfully using the patch on the Adafruit until it was soldered in place. He fixed that by switching to an external antenna. I've never had any success with attached patch antennas but my receivers are inside. The BBB is known to have a bad EMI behaviour. You should not put any sensitive RF components near it, without proper shielding. Attila kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Z3810AS PPS to a Raspberry Pi
On Mon, Mar 23, 2015 at 4:58 PM, Pete Stephenson p...@heypete.com wrote: On 3/23/2015 5:20 PM, Dan Watson wrote: The solution I came up with is very simple but works well. I capacitively couple the signal into a MOSFET which triggers a monostable 555 circuit. This generates a nice clean ~100ms pulse that I send to the PI, and an LED. Because who doesn't like blinking LEDs? For NTP the 555 is good enough but for any kind of precision timing (where nanoseconds mater) the capacitive coupling and 555 would introduce a LOT of noise. But NTP works at the microsecond level.I'm surprised to can't get the Pi to interrupt on the raising edge of the PPS and that you had to make the pulse longer. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Comparing the BeagleBone Black Raspberry Pi asNTP servers
Folks, Many thanks for all your comments. I am now undertaking tests with the stripped-down Console build of the OS. With both the RPi and the BBB I started with what the typical user might install rather than any special version (indeed, it's built into the BBB). It seems that while many services are enabled and run by default on the BBB, this is not so on the RPi, and hence the great difference in CPU load. Early results are that this does not make a lot of difference to what NTP on the card reports, but it does significantly affect the view from outside, i.e. what an NTP client might see from an NTP server. Specific replies: Graham: The other thing that will help is getting rid of the cape-manager system you are using, that is file i/o based. There is a lot of file scanning going on that is not useful in time critical applications. Yes, but I have no idea how to do that. There seems to be a peculiarity in that with the full OS gpsd works as expected, but it doesn't start automatically with the console OS. It does run when started by hand, and I have used dpkg-reconfigure to try and make it auto-start. For the moment, I will leave that as one of the BBB's unexplained mysteries! Attila, Mike: You will see that I have taken your advice and used the console OS. Likely I will not use the BBB for much else as the RPi 2 is more powerful and has a much wider support base. Attila: Thanks for the pointer to the pre-built buildroot images, but they note: Since that time, BBB support was merged upstream, so this is really, really old. Please, please, don't use this in new projects. I'm really only interested in what they typical user might download or find pre-installed. Chris: Yes, the two /etc/ntp.conf are identical, with the possible exception of a leapsecond file not yet being configured for the BBB. Paul: The patch antenna on the Adafruit does work here much of the time, but it is smaller than the patch in the magnetic mount antenna I ended up using. Compared to the naked Adafruit module, a ublox M8Q module and mag mount antenna is noticeably better for indoor use here, and on RPi cards other than the one in this test I've switched to these units: http://ava.upuaut.net/store/index.php?route=product/productpath=59_60product_id=117 Paul: I agree that the table could be improved, but rather than remove information I have emboldened that for the two servers which the client is testing. The table is due for a full update once today's running is completed without interruption. Wolfgang: I agree with your comments, but I am comparing more out-of-the-box rather than special builds etc. To show how things changed between the two OS versions I added a comparison here: http://www.satsignal.eu/ntp/BBB-vs-RPi.html#OS-comparison Many thanks all for your help. Tomorrow I will update the table, and I'm sure that the BBB will win out under both measures. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Z3810AS PPS to a Raspberry Pi
On 3/23/2015 5:20 PM, Dan Watson wrote: The solution I came up with is very simple but works well. I capacitively couple the signal into a MOSFET which triggers a monostable 555 circuit. This generates a nice clean ~100ms pulse that I send to the PI, and an LED. Because who doesn't like blinking LEDs? I laid out a small PCB and ordered a few boards so that I can drop it right onto the GPIO header of the Pi. I have attached a picture of the board, as well as a capture of the input and output waveforms. Looks nice: your surface-mount soldering looks great. The blue trace is the PPS signal from the GPSDO on the gate of the MOSFET, and the yellow trace is the output of the 555. After a couple days of settling, NTP stats on the Pi seem comparable to other GPSs I've tried, but I'll have to collect more data to really be sure of the performance. I think this circuit could also be used to translate PPS signals from other items of equipment to proper logic pulses. Lots more experimenting to do... I've been looking at doing something similar once my Thunderbolt arrives. Out of curiosity, how much does the 555 timer delay the PPS signal? Is it consistent? What's the rise time? Anyway, if anyone is interested in more information about the circuit or board let me know. And comments are welcome. I'd definitely be interested in the board. Any chance of modifying it for through-hole components? My SMT soldering skills are pretty bad. If you can send me the schematic I'd be happy to try modifying it for through-hole components. Cheers! -Pete ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] ADEV noise floor vs counter gate time
Hi Bill, I'm travelling at the moment, but I had another go just now and it has stopped wiping my details when I press the save button so hopefully that means it is fixed. I must just have been unlucky and picked a glitchy day (this was at the end of last week). Though, now that I've downloaded NI-VISA and got that working I probably don't need to download tek-VISA. Best Regards, James -Original Message- From: Bill Byrom t...@radio.sent.com To: time-nuts time-nuts@febo.com Sent: Sun, 22 Mar 2015 20:28 Subject: Re: [time-nuts] ADEV noise floor vs counter gate time Was the website problem this past week? The main Tek US website was acting up for a while one day this week, but seems to be fine now. I have no insights on European access. -- Bill Byrom N5BB On Sun, Mar 22, 2015, at 07:10 AM, James via time-nuts wrote: Hi Bill, Thanks for the pointers. I should say that my results reported so far have been with my older TTi TF930 reciprocal counter, not with my FCA3100 which I have only just got (it arrived a few days ago) and I'm in the process of writing software to talk to it via the USB. I did discover the website, in fact I'd downloaded the manual before buying the counter, and it is fortunate I did because the website for me didn't work - I'm currently talking to Tek support about it. The problem is that to download software you must have your details registered. Every time I register my details and press the save button the site wipes all my details and returns to a blank form. When I try to down load the software it then stops me and tells me to update my details. I update my details and it blanks the form and so on... slightly frustrating. I've tried both Firefox and IE. The other thing is that the manuals don't show on the European site (I'm in the UK), you click on them but the download screen just shows a blank line. I got round this by going to the international site and just closing the screen asking me for my area rather than responding to it - I had to do this several times. I have now downloaded NI-VISA and have managed to do a bit of talking to the instrument over USB though I've not yet had time to do this properly. So in summary - I'm pleased with my counter but the Tek website for Europe at least has some serious bugs which hopefully will be fixed soon. The Tek support person I spoke to on the phone was helpful but she wasn't in a position to fix the web site issues directly so has forwarded my case to Tek IT. I intend repeating my TTi TF930 experiment with my FCA3100 when I've got everything working ok and am looking forward to seeing the results. James -Original Message- From: Bill Byrom t...@radio.sent.com To: time-nuts time-nuts@febo.com Sent: Sun, 22 Mar 2015 2:27 Subject: Re: [time-nuts] ADEV noise floor vs counter gate time Hi, James. I'm a Tektronix RF Application Engineer in Dallas and thought I would throw in a few points about your FCA3100 (if you haven't read up on these already): All Tektronix manuals and technical reference documents can be downloaded for no charge on our website (http://www.tek.com), but some items may require you to register and sign in. The detailed specification and performance verification document (document number 077-0495-01) has many details about the specifications, and is at: http://www.tek.com/frequency-counter-supplies/mca3027-manual/fca3000-and-fca3100-series-mca3000-series All downloadable files for this product can be found in the list at: http://www.tek.com/search/apachesolr_search/fca3000 If you have a used counter, be sure you check the firmware version and update it if needed. If your exact model is FCA3000, you have a 300 MHz counter with 100 ps single-shot resolution. This counter has reciprocal counter features (based on a 10 ns main counter time resolution), but also uses 100 ps RMS jitter interpolation to determine edge location with an additional X100 resolution. When the initial edge of the signal you are measuring is detected, the interpolater resolves this edge with 100 ps resolution relative to the internal 10 ns clock. After the desired measurement interval, the final edge is also resolved with 100 ps resolution, and the number of signal edges and interpolated intitial-to-final time are used to determine the frequency (for example). The analog interpolation circuit uses a constant current charging a capacitor with a sampler and A/D converter. Counting a 100 MHz signal, this provides 12 digits of resolution per second of measurement interval. -- Bill Byrom N5BB On Wed, Mar 18, 2015, at 05:49 PM, James via time-nuts wrote: Hi Dave, Thanks for another detailed response. I've now programmed a version of my code that attempts to recover the raw data by trying different counts up and down from the nominal and finding the one with the
Re: [time-nuts] Comparing the BeagleBone Black Raspberry Pi as NTP servers
The other key key key item is make sure you hand build yourself a 3.14 or .16 kernel. NS On Mon, Mar 23, 2015 at 2:30 AM, Attila Kinali att...@kinali.ch wrote: On Sun, 22 Mar 2015 16:41:56 -0400 Paul tic-...@bodosom.net wrote: 1) Did you start out using the attached patch antenna? D Drown implies successfully using the patch on the Adafruit until it was soldered in place. He fixed that by switching to an external antenna. I've never had any success with attached patch antennas but my receivers are inside. The BBB is known to have a bad EMI behaviour. You should not put any sensitive RF components near it, without proper shielding. Attila kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
