[time-nuts] Do you know the correct time?
I thought many of you would be interested in this article : http://www.devmonkey.edn.com/blog/jon-titus-blog/how-do-you-know-correct-time?cid=Newsletter+-+EDN+on+Development+Tools ___ 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] Using digital broadcast TV for timing?
I'm not completely convinced that DTV has been eliminated as a source, but it would take some study (and discussions with the DTV providers). There may be something there. The problem you have is that so many (most, if not all) stable rf signal sources are derived from GPS today, so that in the EXTREMELY unlikely event that all (24+) GPS sats went off the air, many of those sources would all be affected to one degree or another. You might look at the Russian Glonass system, the European Gallileo system (which is only in prototyping stage), and possibly the Chinese Beidou NAVSATS. Gallileo and Glonass work similar to GPS, but Beidou is a different beast. There are receivers that use both GPS and GLONASS, but I don't have any direct experience with them. WWV (and related HF time signal sources) are an obvious alternative source. NIST operates WWV transmitters at 2.5, 5, 10, 15 and 20 MHz from Fort Collins, CO, and WWVH from Hawaii. These signals are locked to Cs standards. There are other HF time signals from Canada, etc, you might check out. Depending on what you want to do, you might just consider synchronizing a Rb, or a bank of Rb's to GPS. Then if GPS went away, the Rb's would free run for a considerable time. "Considerable" needs to be defined by your timing requirements, and duration, in the non-GPS environment. And then, of course, there are Cesium standards available, if you have deep pockets. Jerry Finn AG6HH ____ From: Chris Albertson To: jerryfi ; Discussion of precise time and frequency measurement Sent: Wednesday, February 8, 2012 9:13 PM Subject: Re: [time-nuts] Using digital broadcast TV for timing? On Wed, Feb 8, 2012 at 7:48 PM, jerryfi wrote: > Thanks Paul. You and Bob Camp provided some good updates/info. It may > present enough of a challenge/reward for someone to examine further. I'm > with you on the available time front - too many other projects/commitments to > pursue further myself. I'll be interested if Chris, or someone else, can > make some headway though. OK if not DTV what other common signal that you could pick up without use of exotic equipment (so this entirely eliminates rotating neutron starts or "pulsars") what else can you get that has decent timing other then GPS and CDMA. I'm not giving up on DTV yet. The video signal is compressed so it may be basically white noise but I bet it is wrapped in some transport like packets that are regular. In practice GPS works well but a question came up here "What could you use if GPS went away?" I said "I bet there is some signal all around us that just happens to have precision timing embedded in it. Maybe DTV maybe it's direct broadcast TV. -- 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] Using digital broadcast TV for timing?
Thanks Paul. You and Bob Camp provided some good updates/info. It may present enough of a challenge/reward for someone to examine further. I'm with you on the available time front - too many other projects/commitments to pursue further myself. I'll be interested if Chris, or someone else, can make some headway though. Jerry AG6HH From: paul swed To: jerryfi ; Discussion of precise time and frequency measurement Sent: Wednesday, February 8, 2012 7:07 PM Subject: Re: [time-nuts] Using digital broadcast TV for timing? All gone these days in the US. Indeed I can speak to the CBS network it was driven by CS references in the 80s and 90s. I used CBS for aligning my references Xtal oven oscillators that were never ever turned off in a large facility that uplinked all 8 CBS regions and 22 other cable networks. Unfortunately few could get to that color burst signal as devices called frame synchronizers came into play from the 80s to the 90s. They would strip off that burst and insert the local reference of generally much lower quality. As far as todays digital TV signals they can contain significant jitter. But its actually trickier then that and I honestly have to say I am not sure that you might not be able to get something useful. Several interesting points. Many of the television transmitters do use GPS referenced sources. Its an interesting exploration. I simply don't have the time though. Regards Paul WB8TSL On Wed, Feb 8, 2012 at 7:38 PM, jerryfi wrote: A bit off topic, but historically related back in the 70's, I tapped off the color burst > >oscillator in my TV (a Heathkit) to get a 3.579545 MHz (315/88 MHz) >source to > >calibrate my homebrew frequency counter. The TV's color burst oscillator was >phase > >locked to the color burst signal on the broadcast signal (which was on the >"back > >porch" of the hori sync signals). Supposedly, the networks were locked to >Cesium > >standards traceable to NBS for LIVE broadcasts, such as news and sports. Taped > >programs, of course, were not usable as an accurate source. In any case, that >signal >served my purposes at the time (providing a reference for calibrating my >counter that >was more accurate than anything else available to me). > >I'm not sure if, what, or where analog TV is still broadcast, but I think >there are still a > >few stations (low power) around. You might still be able to use that signal, >IF you can > >dig it out of your old analog TV. ;-) I do have analog tv's hooked up to my >cable > >box - I suspect that live broadcasts would still have an accurate color burst, >so maybe > >I think the other methods discussed here (ie, GPS) would provide easier and >more > >reliable timing sources. ;-) > > >Trying to locate the appropriate signal(s) in a digital TV today would be >interesting. > >Just as a historical aside. > > > >Jerry Finn >Santa Maria, CA > > > >> Date: Tue, 7 Feb 2012 18:01:26 -0800 >> From: Chris Albertson >> To: Discussion of precise time and frequency measurement >> >> Subject: [time-nuts] Using digital broadcast TV for timing? >> Message-ID: >> >> Content-Type: text/plain; charset=ISO-8859-1 >> >> GPS requires a good view of the sky, Hard to do in say the 7th floor >> of a 40 story building if you have no windows. I'm wondering about >> using the new digital TV signals for timing. >> >> I'm pretty sure there is time code in the signal and I'm pretty sure >> the bits are clocked at a very accurate rate. Also TV receivers are >> very easy to find and put "hooks" into. I'd bet the broadcast TV >> signal could be almost as good as GPS. >> >> The plan is to try and phase lock a local oscillator and use a very >> long time constant on the loop filter. I bet the TV transmitters are >> locked to GPS and over a long enough time are as good as GPS. Also in >> many cities there are many TV transmitters, should be able to take >> advantage of that. >> >> Before I try some experiments anyone want to tell me why I'm wrong? >> -- >> >> 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. > ___ 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] Using digital broadcast TV for timing?
Thanks Bob. I haven't kept up on TV broadcast standards & methods, obviously. It might be interesting (for the curiousity challenged) to pull out the color osc signal and compare to another accurate source (ie GPS) for live broadcasts. While delayed, I would think that the signal freqs would still need to be maintained... hmmm, maybe not... interesting science project... anyone? anyone? ;-) Jerry > From: Bob Camp > To: jerryfi ; Discussion of precise time and frequency > measurement > Sent: Wednesday, February 8, 2012 4:43 PM > Subject: Re: [time-nuts] Using digital broadcast TV for timing? > > Hi > > The whole cesium lock approach died back in the 90's. These days your local > station buffers / retimes / reframes everything. If you are lucky they use a > Rb for the timing. > > Bob On Feb 8, 2012, at 7:38 PM, jerryfi wrote: > A bit off topic, but historically related back in the 70's, I tapped off > the color burst > oscillator in my TV (a Heathkit) to get a 3.579545 MHz (315/88 MHz) > source to > calibrate my homebrew frequency counter. The TV's color burst oscillator was > phase > locked to the color burst signal on the broadcast signal (which was on the > "back > porch" of the hori sync signals). Supposedly, the networks were locked to > Cesium > standards traceable to NBS for LIVE broadcasts, such as news and sports. > Taped > programs, of course, were not usable as an accurate source. In any case, > that signal > served my purposes at the time (providing a reference for calibrating my > counter that > was more accurate than anything else available to me). > > I'm not sure if, what, or where analog TV is still broadcast, but I think > there are still a > few stations (low power) around. You might still be able to use that signal, > IF you can > dig it out of your old analog TV. ;-) I do have analog tv's hooked up to my > cable > box - I suspect that live broadcasts would still have an accurate color > burst, so maybe > I think the other methods discussed here (ie, GPS) would provide easier and > more > reliable timing sources. ;-) > > Trying to locate the appropriate signal(s) in a digital TV today would be > interesting. > > Just as a historical aside. > Jerry Finn > Santa Maria, CA ___ 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] Using digital broadcast TV for timing?
A bit off topic, but historically related back in the 70's, I tapped off the color burst oscillator in my TV (a Heathkit) to get a 3.579545 MHz (315/88 MHz) source to calibrate my homebrew frequency counter. The TV's color burst oscillator was phase locked to the color burst signal on the broadcast signal (which was on the "back porch" of the hori sync signals). Supposedly, the networks were locked to Cesium standards traceable to NBS for LIVE broadcasts, such as news and sports. Taped programs, of course, were not usable as an accurate source. In any case, that signal served my purposes at the time (providing a reference for calibrating my counter that was more accurate than anything else available to me). I'm not sure if, what, or where analog TV is still broadcast, but I think there are still a few stations (low power) around. You might still be able to use that signal, IF you can dig it out of your old analog TV. ;-) I do have analog tv's hooked up to my cable box - I suspect that live broadcasts would still have an accurate color burst, so maybe I think the other methods discussed here (ie, GPS) would provide easier and more reliable timing sources. ;-) Trying to locate the appropriate signal(s) in a digital TV today would be interesting. Just as a historical aside. Jerry Finn Santa Maria, CA > Date: Tue, 7 Feb 2012 18:01:26 -0800 > From: Chris Albertson > To: Discussion of precise time and frequency measurement > > Subject: [time-nuts] Using digital broadcast TV for timing? > Message-ID: > > Content-Type: text/plain; charset=ISO-8859-1 > > GPS requires a good view of the sky, Hard to do in say the 7th floor > of a 40 story building if you have no windows. I'm wondering about > using the new digital TV signals for timing. > > I'm pretty sure there is time code in the signal and I'm pretty sure > the bits are clocked at a very accurate rate. Also TV receivers are > very easy to find and put "hooks" into. I'd bet the broadcast TV > signal could be almost as good as GPS. > > The plan is to try and phase lock a local oscillator and use a very > long time constant on the loop filter. I bet the TV transmitters are > locked to GPS and over a long enough time are as good as GPS. Also in > many cities there are many TV transmitters, should be able to take > advantage of that. > > Before I try some experiments anyone want to tell me why I'm wrong? > -- > > 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.
