Re: [time-nuts] ntp and asymmetric delays
I was going to post my ntp output and ask for an opinion, then this discussion popped up. It would appear that asymmetric delays are the exact explanation for what I am seeing. Is that a reasonable assumption? It does seem to be rather consistent throughout the day, however. The reason for checking against the net when I have a GPS source is that I want ntp to continue if/when there is no PPS. Is there any way to inform ntp of the asymmetry? Thanks, -- Thomas Valerio Every 20.0s: /usr/sbin/ntpq -n -c pe pe Tue Oct 11 12:37:33 2016 remote refid st t when poll reach delay offset jitter == x127.127.28.0.NMEA. 0 l4 16 3770.000 -30.300 36.009 *127.127.28.1.PPS.0 l3 16 3770.0000.001 0.000 -208.53.158.34 216.93.242.123 u9 64 377 17.2022.907 0.188 +208.100.4.52216.86.146.462 u 64 64 377 16.6122.332 0.193 +208.69.120.241 142.66.101.132 u5 64 377 24.2581.688 0.223 -128.118.25.3130.207.244.240 2 u 53 64 377 40.4294.956 2.577 > Hi > > NTP can *not* detect âcommon modeâ asymmetric delay. Having a local > GPS does not count in this respect. What does count is an NTP client / > server sitting in your home trying to figure out what time it is only > by hooking to the internet. > >To do this it must do a few things: > > 1) Get a signal out through the (slow / long lag) upload channel on your modem. > 2) Route that signal through the cable guyâs low capacity upstream network to >one of his (at best) two or three gateways to your local empire. These may >or may not be in the same state you live in. > 3) Fly the signal over the backbone to whatever server is involved. > 4) Fly a signal back over the backbone to possibly another set of gateways. > 5) Route that signal through the cable guyâs high capacity downstream network. > 6) Run it through the (quite fast / low lag) downstream channel on your modem. > > Steps 1,2,5 and 6 are common to every single server you try to access. If your > modem has an âupstreamâ lag of (say) 101 ms and a âdownstreamâ lag > of (say) 1 ms, every server you contact will have a round trip time of at > least 102 ms. They *may* have more than this, but none will ever have less. > > As the day progresses and various groups pop on and off the system in your state, > the usage of the upstream and downstream channels changes. It is not unreasonable > to guess that both change as a percentage. If that guess is correct, your upstream > varies by significantly more than your downstream. That will get into NTPâs loop > correction stuff as well. > > You *might* ask, how about pings? Well, you *might* look into it and find that > your local cable system recognizes pings at a very low level and preferentially > routes them. Yes, thatâs hogwash and nobody would ever do it â¦.. except > thatâs the way it works here with my internet. The network can be completely > dead and pings (along with other ICMP traffic) will get through. Hmmmâ¦.. > > You are indeed a guy with 5 watches to check against. The gotcha is that every > single one of them has been set fast or slow by the same amount. > > Bob > >> On Oct 6, 2016, at 11:03 AM, Chris Albertson >> wrote: >> >> I still think NTP can detect asymmetric delays. Only it can't know that >> is >> what it is detecting. What else generate those offset numbers? Yes >> it >> could very well be that MRS is running slow but I doubt that is the >> case. >> And I really doubt your GPS' PPS is off by even one microsecond.A >> good >> bet is that ALL the results we see is because the real-world >> communication >> path is different from the assumption NTP makes about communications >> paths. >> >> In practice what NTP sees is all due to the Internet and not so much the >> reference clocks. Your data shows this. 162.23.41.10 .MRS has >> different >> stat depending on who is looking at it. So those billboards are showing >> network stats not server stats. (but NTP can't know that for certain so >> it >> is obliged to call them server stats) >> >> This is 2016. Almost any reference clock you are likely to use will be >> pretty much dead-on, at least to within the precision that NTP works >> with. >> So anything those billboards say is really about the communications >> paths. >> But NTP has no theoretical right to assume the cause of what it sees. >> Theory and practice differs, In theory NTP can not detect asymmetric >> delay but in prac
Re: [time-nuts] controlling instruments using USB
Have you looked at alien to convert the rpm to a deb?
https://www.google.com/#q=alien+package+conversion
> Semi-off-topic..
>
> I've got a bunch of Keysight/Agilent/HP instruments with USB interfaces
> that I want to control from Python. On Mac and PC, the PyVisa library
> works great (either the one with the NI back end or the python only back
> end )
>
> But, on Ubuntu, there's no way to install the NI drivers (RH install
> only, and Ubuntu is debian..)
>
> So, I've been doing usbtmc, which sort of works. (after figuring out
> all the udev rules stuff)
>
> If I do something like this from the python interpreter:
>
> >>> import usbtmc
> >>> myinst = usbtmc.Instrument( mfr, product)
> >>> myinst.write('some command')
>
> it works fine.
>
> But if I put the same three linesin a .py file and run it, it doesn't
> always work.. sometimes, you need to send the command twice.
>
> It seems it might be a timing thing (in libusb or usbtmc?) but putting
> some sleep() in between connecting to the instrument and doing the write
> doesn't seem to work all the time.
>
> Very curious.
>
> Any ideas?
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[time-nuts] Dead tree material: Ships, Clocks, and Stars: The Quest for Longitude
I usually don't have very much to contribute to this list, a lot of what gets discussed here is a bit above my pay grade, so I mostly just read and hope some of it sinks in. Also not sure how much interest there is on this list in dead tree material. That being said, I was at Ollie's Bargain Outlet, https://en.wikipedia.org/wiki/Ollie's_Bargain_Outlet and I saw four copies of Ships, Clocks, and Stars: The Quest for Longitude Hardcover November 4, 2014 by Richard Dunn (Author), Rebekah Higgitt (Author), http://www.amazon.com/Ships-Clocks-Stars-Quest-Longitude/dp/006235356X for $10. I was thinking of buying a copy for myself and wondered if there might be some interest from others. According to the USPS web site this book can be shipped at media mail rates for less than $5, so at $20 on your doorstep this book is about $15 cheaper than it appears to be available any where else. Any interest? Thomas Valerio ___ 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] Just When You Thought It Was Safe ....
Well if you look at his sales counts it isn't working very well, and now after the latest comments he might have to deal with a backlash effect. Right now I'm definitely in at $60-70, unlikely but possibly in at $100, although that is still hard to justify, $150 not a chance. I'd buy a James Miller GPSDO before I would buy a KS24361 at $150. It's not nearly the same bang for the buck adev wise as a KS24361, even at $150, but at least I get some serious space savings and I am far more confident that the money is going to an honest seller. -- Thomas Valerio > It is a common fishing technique, and the guy has done this > several times over the last year, or so. > > When his sales dry up, he drops the price to $100, and then > waits for a sale I'm pretty sure that he monitors this > group for news of the new low price to leak out... and then > quickly he bops the price back up to $150. > > I considered buying one about two such casts ago, and missed > the low price point... and then decided that I didn't really > need to play this game with the seller. > > -Chuck Harris > > > > paul swed wrote: >> Bob >> Just took a look and the pair seems to still be at $150. Maybe it was a >> special? >> The ovens are as you say $25 each and shipping for either 1 or 2 is >> $18.75. >> Regards >> Paul >> WB8TSL >> >> On Mon, Jul 27, 2015 at 8:44 PM, Bob Camp wrote: >> >>> Hi >>> >>> For all of you who dropped off the list back around Christmas and >>> decided >>> to re-join now that the KS box yack has died down â¦.. >>> >>> The usual auction site now has the pair selling for $100 and the âno >>> GPS >>> insideâ part of the pair selling for $25 or two for $50. >>> >>> Mighty fair prices considering that they are new old stock rather than >>> salvage units. >>> >>> (Yes I suppose that if we all hold off, they could go lower still. They >>> also could head over for scrap metal reclamation) >>> >>> Bob ___ 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] Low cost GPS for model aircraft
You might want to check out http://diydrones.com/ as well. Thomas Valerio > This chatter about model aircraft GPS got me to wondering if there now > off-the-shelf flight control systems for model planes that will do nav > and/or attitude control? I know there are mini-gyros, but I think they are > only good enough for attitude control. > > Last time I was into this, if you lost radio contact the model was gone or > had crashed.. > > -John ___ 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] Radio Shack GPS Module
The Adafruit breakout board looks very appealing. I also already own
several Trimble Resolution T's and something I've been wondering about for
a while is whether there is any downside, difficulties or problems with
mounting a bare GPS receiver board inside a computer case. If there are
problems, would enclosing it in a shielded enclosure ameliorate those
problems? Has anyone on the list done this?
Thanks,
Thomas Valerio
> From: Tim Shoppa
>
> Very likely the Parallax PMB-648, a SirfStar III. A fair number of local
> radio shack stores have Parallax and Arduino stuff on the shelves without
> a Radio Shack part number.
>
> http://www.parallax.com/go/GPS
> ===
>
> If you want PPS output, and TTL/CMOS levels for serial are OK, this is a
> rather nice little module, cheaper than the Radio Shack item:
>
> http://www.adafruit.com/products/746
>
> Lower power as well, and more sensitive, and you can add a battery for
> backup.
>
> Cheers,
> David
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Re: [time-nuts] Posting Rules
I think I pretty much agree with Perry. This list has occasionally gone quite aways OT, but it invariably finds its way back, and certainly more than quickly enough. However, a mother replacement does absolutely nothing to speed up the process, least of all a sanctimonious, holier-than-thou one. Thomas Valerio >> Charles wrote: Please keep your political comments to yourself and off >> the list (however humorous you might think they are). This is simply >> not the place for them. >> > Charles, > > On the two lists we both subscribe to, you always seem to have something > to say about almost every post. Often it falls into the category of > Mother says: now don't forget to do ___. (You can fill in the > blank space.) I see you doing this in a very condescending manner. > > On the R-390 list, I've forgotten more about the R-390A receiver > than you will ever know. I was trained on them, serviced them in > the military, developed parts kits for them, wrote the Y2KR3 manual > and have had a number of published technical articles about them. > At least on the R-390A radio you have done nothing that I'm aware > of and I follow information on it very carefully. > > You don't own or administer this list. All members have the right to > make civil posts of their opinion whether others agree with them on > not. My mother died many years ago and I don't need you to be her > replacement. You have the same privilege of all of us to post or delete. > > Kind Regards, > Perrier ___ 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] RFX GPSDO - Anybody played with one of these?
Actually, it was in Nuts & Volts as well, and I was thinking about posting a similar query to the list, but my incentive and my interest pretty much went negative when my cursory investigation revealed that price information appeared to be non-existent. IMHO for pretty much *everything* that is for sale, if you have to ask for the price it is a scam. The message that I get from non-existent pricing information is that this product's price/value proposition can't stand on it's own, the only way you will be convinced to purchase, at a usually inflated price point, is after the snake oil sales people have had a chance to get their spiel out. Thomas Valerio > Offhand I can not think of any reason it could not exist but if you > have to ask for the price, then I suspect it will be too expensive. > > On Sun, 30 Sep 2012 19:40:47 -0700, Skip Withrow > wrote: > >>Hello Nuts, >>Just saw this mentioned in Circuit Cellar, just wondering if it really >>exists, how much they are asking, and if anyone has played with one >>yet? >> >>http://www.rfx.co.uk/pdfs/GPS_OCXO_1300_10_module.pdf >> >>Regards, >>Skip Withrow ___ 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] Serial to Excel utility.
NP, http://freecode.com/projects/np might be a good starting point. Nic McLean wrote: Sorry folks for the slightly OT post. Does anybody know of a utility that will import and parse the serial bit stream from a GPS and put values into a couple of cells in an Excel spreadsheet? Regards, Nic VK2KXN / VK5ZAT ___ 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.
