Hi There's always the ever popular 5370 (a or b) off auction on the cheap ...
The box we had did indeed have a pretty good time stamper. It would take in "anything or everything" and ultimately tell you what was happening with it. I don't recall the GPS data being good to the ~20 ps level. Simply doing <1 ns level time transfer would be a major upgrade over what most of us have available. If you could do a number of "shots" over an hour or so that certainly would do me a *lot* of good. That of course assumes I'm borrowing a very good standard on the other end. Bob On Mar 15, 2010, at 9:40 PM, Bruce Griffiths wrote: > According to the available documentation for one variant of the NIST box, it > had (apart from the GPS receiver) a multichannel time stamping counter to > time stamp PPS pulses from external signal sources (generated using a > programmable divider so that any source with a frequency of up to around > 100MHz or so that was nominally a harmonic of 1Hz could be used). > The timestamp resolution of was about 25ps. > > Bruce > > > > Bob Camp wrote: >> Hi >> >> One could always use the ever popular super cooled sapphire resonator >> oscillator and an equally handy optical ion standard. >> >> -------------------- >> >> Anything that involves comparing same to same is vulnerable to all sorts of >> common mode effects. Ensembles of cesiums all made on the same line can have >> issues. Even having something like (yikes!) WWVB to throw in the mix will >> help rule out part of the errors that creep in. >> >> One thing we haven't talked about (but could) are time transfer setups via >> common view GPS. Back when we had a NIST box it did them under robotic >> control. Judging from the data plots it did a very good job. >> >> There really wasn't a lot in the silly box. Their system did indeed use a >> (at that time) fancy antenna and a pretty good receiver. It's not clear to >> me that the 1980's technology in the box could not be duplicated today for a >> lot less than they put into it. Anything you can toss into the mix is a good >> thing. With good enough time transfer you could use the H-Maser in somebody >> else's basement ..... >> >> Bob >> >> >> >> On Mar 15, 2010, at 8:55 PM, Bruce Griffiths wrote: >> >> >>> Unless you have a CSO or a hydrogen maser absolute measures of ADEV and >>> phase noise arent feasible for the range of Tau of interest. >>> Even an indirect method such as measuring the location of the apparent >>> minimum in ADEV between the GPS SV constellation observables and the OCXO >>> when it is undisciplined depend heavily on the ADEV characteristics of the >>> OCXO being used. >>> >>> Bruce >>> >>> WarrenS wrote: >>> >>>> yeah, >>>> So many variables, ALL the more reasion to just see what the overall >>>> effect is on the more common type of GPSDO receviers at a few sites. >>>> So did you have a better plan? >>>> >>>> ws >>>> >>>> **************** >>>> Bruce Griffiths Added: >>>> >>>> >>>>> WarrenS wrote: >>>>> >>>>> Bruce wrote: >>>>> >>>>>> "Which antenna performance metric do you have in mind?" >>>>>> >>>>> Could do GPSDO hold over performance, but that would not be much of >>>>> a test of the antenna. >>>>> How about the antenna's effect on the ADEV Osc noise and Phase noise. >>>>> What else does the Time Nut care about? >>>>> >>>>> >>>>>> Since the better timing receivers use carrier phase ... >>>>>> >>>>> I don't remember you ever finding ANY Time Nut that is now using one. >>>>> So may be simpler for now to just stick to the more common type of >>>>> GPSDO in use. >>>>> >>>>> >>>> The Motorola M12+T and iLotus M12M use carrier phase smoothing of the >>>> code phase observables. >>>> >>>> Its highly likely that a number of the better performance GPS timing >>>> receivers also use carrier phase smoothing. >>>> >>>> Thus whether one is aware of it or not the antenna carrier phase >>>> properties are likely to be of some importance. >>>> >>>> In the absence of complete information on how your particular GPS timing >>>> receiver uses carrier phase and code phase observables, the best you can >>>> do is compare the performance of a range of antennas using a given >>>> timing receiver. >>>> >>>> Such results will only apply to a particular site and receiver. >>>> Specifying the pertinent characteristics (eg isolated on a flat plain, >>>> surrounded by a set of hills, mountains which obscure the sky below 10 >>>> degrees, surrounded by trees that obscure everything below 40 degeees >>>> elevation, etc) of your antenna location and the particular GPS receiver >>>> used will be helpful to others in selecting an antenna that suits their >>>> budget, receiver, antenna location constraints, etc. >>>> >>>> Bruce >>>> >>>> >>>>> ws >>>>> >>>>> ************* >>>>> Bruce said: >>>>> >>>>> Which antenna performance metric do you have in mind? >>>>> There are several, some of which are considered in the paper: >>>>> http://www.novatel.com/Documents/Papers/effectofantenna.pdf >>>>> >>>>> Since the topography surrounding the antenna, its height and location on >>>>> the Earth all affect measured performance any comparative measurements >>>>> should use the same receiver and antenna location. >>>>> >>>>> Some estimates for the effect of multipath on code phase receivers can >>>>> be found: >>>>> >>>>> http://bbcr.uwaterloo.ca/~wzhuang/papers/iee95_gps.pdf >>>>> >>>>> http://bbcr.uwaterloo.ca/%7Ewzhuang/papers/iee95_gps.pdf >>>>> >>>>> Since the better timing receivers use carrier phase smoothing of the >>>>> code phase timing, both the carrier phase and code phase performance of >>>>> the antenna are important. >>>>> >>>>> A phased array antenna like the one in the following papers may provide >>>>> better performance than alternative antennae: >>>>> >>>>> http://www.navsys.com/Papers/0001002.pdf >>>>> http://www.congrex.nl/07c12/papers/day1_s1_paper05_Konovaltsev.pdf >>>>> >>>>> Some measurements with geodetic antennae: >>>>> http://www.fig.net/pub/fig2008/papers/ts05g/ts05g_03_eventzur_shaked_2816.pdf >>>>> >>>>> >>>>> Comparison of code phase and carrier phase time transfer: >>>>> http://tycho.usno.navy.mil/ptti/ptti2004/paper41.pdf >>>>> >>>>> Bruce >>>>> >>>>> ****************** >>>>> WarrenS wrote: >>>>> >>>>>> Brian wrote: >>>>>> >>>>>> >>>>>>> "There were also comments about surveying and timing antennas." >>>>>>> >>>>>> Those may of been from me, unsuccessfully trying to make a point of >>>>>> the difference between what is 'Best' and what is 'GOOD enough'. >>>>>> >>>>>> >>>>>>> "about every national timing laboratory uses choke ring antennas. >>>>>>> ... for timing stability reasons." >>>>>>> >>>>>> Then again they also have multiple CS and Just their Antenna budget is >>>>>> likely more than the annual income of most time nuts. >>>>>> Can you do a test to show IF there is ANY improvement for the AVERAGE >>>>>> time nut when compared to a well setup (Tbolt) GPSDO using a TacoSalad >>>>>> antenna? >>>>>> >>>>>> Would be interesting to see a plot of cost vs. performance for the >>>>>> various antenna types, >>>>>> Scaled to show the performance improvement that the average Time nut >>>>>> would see. >>>>>> The TacoSalad antenna, originally cost me a total of $7.95, And took >>>>>> under 30 seconds to build. >>>>>> That cost should be discounted because those parts had been considered >>>>>> just throw away junk up until now. >>>>>> >>>>>> ws >>>>>> >>>>>> ********************** >>>>>> >>>>>> ----- Original Message ----- From: "Brian Kirby" >>>>>> <kilodelta4foxmike at gmail.com> >>>>>> To: "Discussion of precise time and frequency measurement" >>>>>> <time-nuts at febo.com> >>>>>> Sent: Monday, March 15, 2010 2:09 PM >>>>>> Subject: Re: [time-nuts] Choke Ring Pictures >>>>>> >>>>>> >>>>>> >>>>>>> Dr. Clark passed on a tip that I used. Put the funnel in a microwave >>>>>>> oven and run it and see if the funnel warms up. If it warms up, you >>>>>>> do not use it. I do not know what type of plastic the funnel was >>>>>>> made out of; it was white, semi-transparent. >>>>>>> >>>>>>> There were also comments about surveying and timing antennas. If you >>>>>>> investigate about every national timing laboratory uses choke ring >>>>>>> antennas. Some enclose the antenna unit and they temperature control >>>>>>> it. They do this for timing stability reasons. >>>>>>> >>>>>>> The commercial timing antenna is bullet shaped and is operated >>>>>>> without a ground plane. They are patch antennas. When there is not >>>>>>> ground plane, the antenna picks up best from the overhead and less >>>>>>> towards the horizon. These antennas usually have a lot more gain >>>>>>> (30-50 db vs most normal antennas in the 15-25 db range). >>>>>>> Also in surveying, we cut off the horizon at 15 degrees in software. >>>>>>> A free Army Corp of Engineering manual on GPS Surveying is at >>>>>>> http://140.194.76.129/publications/eng-manuals/em1110-1-1003/toc.htm >>>>>>> The main difference in surveying and timing is in surveying they use >>>>>>> the carrier phase method, were in timing most use a solution derived >>>>>>> from the processing of the coarse acquisition code, in were the >>>>>>> receiver is in a fixed over-determined position . Some timing labs >>>>>>> are using carrier phase method, when they need more resolution. >>>>>>> >>>>>>> Brian - KD4FM >>>>>>> >>>>>>> >>>>>> **************** >>>>>> >>>>>>>> warrens wrote: >>>>>>>> >>>>>> ... >>>>>> >>>>>>>> Preliminary results for the Taco Dish GPS antenna as an indoor >>>>>>>> antenna are looking good. >>>>>>>> Certainly worth considering if your GPS antenna is stuck indoors, >>>>>>>> 'Out of the rain in the living room'. >>>>>>>> I find it best to rise it up near the ceiling such as on an upper >>>>>>>> shelf with nothing above it. >>>>>>>> It would be hard to tell the difference between the GPSDO >>>>>>>> performance obtained from this or the Best outdoor antenna if using >>>>>>>> a Tbolt set to the standard default settings. >>>>>>>> Picture attached >>>>>>>> >>>>>>>> ws >>>>>>>> >>>>>>>> >>>>>>> ************** >>>>>>> >>>>>> >>>>> >>>> >>>> _______________________________________________ >>>> 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. >>> >>> >> >> _______________________________________________ >> 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. > _______________________________________________ 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.
