Actually an HP 5065A in good condition is adequate to characterize the best GPSDOs beyond t=10s or so (see green trace). 5065As aren't that much noisier than passive masers until you get past t=1000 seconds!
On the other hand, a telecom-grade rubidium is nowhere near good enough for GPSDO tweaking (blue trace). -- john, KE5FX > -----Original Message----- > From: [email protected] [mailto:[email protected]]on > Behalf Of Bob Camp > Sent: Monday, March 15, 2010 6:22 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Choke Ring Pictures > > > 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_shak > ed_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 -- [email protected] > >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
<<attachment: gps_refs.gif>>
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