[time-nuts] Re: HP atomic clocks . The cesium tubes in them are no longer any good, {External}

paul swed paulswedb at gmail.com
Tue Oct 11 21:19:30 UTC 2022 

Jim
If the units been off a long time then it is normal to peg. Power it up and
set the switch to some other reading and let it run 2-3 weeks. Maybe take a
quick check once per week. You may find that it comes down. Maybe not. But
it can take a lot of time to clear. The trick to recovery or at least pump
down is a slightly higher power 3500 vdc supply that can supply more than a
few microamps worth of current. Ideally adjustable current limiting. They
are out there for reasonable money on the auction sites. Be careful 3500 V
is nasty.
If you are going to do this there are a few more details. But nothing major.
You maybe 100% right though the Cs maybe used up.
Regards
Paul
WB8TSL

On Tue, Oct 11, 2022 at 3:37 PM Jim Muehlberg via time-nuts <
time-nuts at lists.febo.com> wrote:

> Hi Aiden,
>
> I've just come into possession of a 5061A here at work.  It's was on
> it's way to salvage but I dragged it into my office to add my ever
> increasing pile of "stuff I might need".
>
> In any event, I'd like the detail on how you resurrected the tube.  Mine
> has a serial number indicating 1991 manufacture.  Not sure where we got
> this beast.  If we used it here at the observatory, I'm sure it was on
> until it died. Could have been 10-20 years!
>
> Ion pump current is off scale.
>
> I'm not a certifiable time nut, but I am getting the fever!
>
> Thanks,
>
> Jim Muehlberg
>
> On 2022-10-11 2:17 AM, Aiden Gibson via time-nuts wrote:
> > Hi all, first time replying!
> >
> > Absolutely right about leaving them running on standby, however there is
> a transistor-based "interlock" which will cut power to the tube if a given
> ion pump current is exceeded.
> >
> > I recently brought a 5061A back to life by removing the beam tube and
> running the ion pump overnight with a benchtop HV supply.
> >
> > If they end up being beyond saving, they're still worth hanging onto for
> their fantastic OXCOs!
> >
> > Aiden Gibson
> > ajg0063 at auburn.edu
> >
> >
> >
> > -------- Original message --------
> > From: Greg Maxwell via time-nuts<time-nuts at lists.febo.com>
> > Date: 10/11/22 00:40 (GMT-05:00)
> > To: Discussion of precise time and frequency measurement<
> time-nuts at lists.febo.com>
> > Cc: Lester Veenstra<m0ycm at veenstras.com>, Greg Maxwell<
> gmaxwell at gmail.com>
> > Subject: [time-nuts] Re: HP atomic clocks . The cesium tubes in them are
> no longer any good,
> >
> > Sometimes "dead" tubes will come back to life if you leave the
> > instrument running in standby for a week so that the ion pump has time
> > to pull the pressure back down.
> >
> >
> > On Mon, Oct 10, 2022 at 2:58 PM Lester Veenstra via time-nuts
> > <time-nuts at lists.febo.com>  wrote:
> >> Wrong email subject on original post, Apologies
> >>
> >> Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y
> >> lester at veenstras.com
> >>
> >> -----Original Message-----
> >>
> >>
> >> Any suggestions on how to make use of this offer from a local ham?
> >> - - - - - -
> >> "There are four HP atomic clocks sitting in the back room at the
> University.  The cesium tubes in them are no longer any good, and we no
> longer have the unused spare cesium tube, but it was bad anyway. The clocks
> do contain a stabilized 5 MHz crystal oscillator which was locked to the
> cesium tube when they were working.
> >>
> >> I am pretty sure I can get one or two of these clocks for you. "
> >>
> >> - - - - - -
> >> I hate to decline an offer of HP equipment.
> >>
> >> Does anyone (any company) offer new replacement tubes?
> >>
> >> Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y
> >> lester at veenstras.com
> >>
> >> 452 Stable Ln (HC84 RFD USPS Mail)
> >> Keyser WV 26726
> >>
> >> GPS: 39.336826 N  78.982287 W (Google)
> >> GPS: 39.33682 N  78.9823741 W (GPSDO)
> >>
> >>
> >> Telephones:
> >> Home:                     +1-304-289-6057
> >> US cell                    +1-304-790-9192
> >> Jamaica cell:           +1-876-456-8898
> >>
> >>
> >>
> >> -----Original Message-----
> >> From: time-nuts [mailto:time-nuts-bounces at lists.febo.com] On Behalf Of
> Bob kb8tq
> >> Sent: Saturday, February 27, 2021 6:39 PM
> >> To: Discussion of precise time and frequency measurement
> >> Subject: Re: [time-nuts] U-blox teaser
> >>
> >> Hi
> >>
> >>
> >>
> >>> On Feb 27, 2021, at 11:18 AM, Dana Whitlow<k8yumdoober at gmail.com>
> wrote:
> >>>
> >>> Thanks, Bob.
> >>>
> >>> It seems to me that, depending on the positions of sats visible to
> one's GPS
> >>> antenna and the spatial distribution of free electron density in the
> >>> ionosphere,
> >>> the ionospheric contribution to position errors could sometimes largely
> >>> cancel.
> >>> But that observation may (or may not) reflect strongly on one's
> ability to
> >>> get
> >>> accurate absolute time from GPS on "average" days.
> >>>
> >>> During my Arecibo Observatory days we used NIST's TMAS service to keep
> >>> our H-maser-based station clock synced with UTC.  Our user community
> >>> (mainly VLBI and pulsar timing people) seemed pretty satisfied with +/-
> >>> 100ns
> >>> accuracy, so I tried to do better by keeping things well within +/- 50
> ns
> >>> during
> >>> my reign.  IIRC, NIST was claiming that TMAS could produce results
> mostly
> >>> within about +/- 20 ns.
> >>>
> >>> To be honest I'm baffled by how time transfer much better than that
> could
> >>> be achieved in practice.
> >> One way (mentioned about a month back on the list) is a two way transfer
> >> via satellite. The “delay is equal in both directions” assumption is
> pretty good
> >> in this case. Once you have that as a baseline, you can measure the
> performance
> >> of other approaches.
> >>
> >> One of *many* starting points to rumble down this rabbit hole:
> >>
> >>
> https://www.nist.gov/pml/time-and-frequency-division/time-services/common-view-gps-time-transfer
> <
> https://www.nist.gov/pml/time-and-frequency-division/time-services/common-view-gps-time-transfer
> >
> >>
> >> I would suggest starting with David Allan’s paper (referenced in the
> link above) as a
> >> pretty good starting point.
> >>
> >> Bob
> >>
> >>> Regarding Q3, yes I'm aware that *some* GPS receivers do the
> estimation of
> >>> ionospheric delay.  What I was asking was:  Do any of the relatively
> >>> inexpensive
> >>> receivers to which we time-nuts have access do this?  Here I'm
> speaking of
> >>> those being sold for no more than a few hundred USD.
> >>>
> >>> Dana
> >>>
> >>>
> >>>
> >>> On Sat, Feb 27, 2021 at 9:08 AM Bob kb8tq<kb8tq at n1k.org>  wrote:
> >>>
> >>>> Hi
> >>>>
> >>>>
> >>>>
> >>>>> On Feb 27, 2021, at 9:41 AM, Dana Whitlow<k8yumdoober at gmail.com>
> wrote:
> >>>>>
> >>>>> I've long understood that ionospheric delays and variations thereof
> lead
> >>>> to
> >>>>> *position*
> >>>>> uncertainties in GPS navigation receivers, to the tune of perhaps 10m
> >>>>> (2DRMS IIRC).,
> >>>>> and that these are said to constitute the single largest GPS error
> >>>> source.
> >>>>> Q1: Would this not imply timing errors of comparable magnitude (10's
> of
> >>>>> nsec)
> >>>>>       for a single band GPS?
> >>>> Once all the signals “hit” the antenna, the delays are mostly common
> mode.
> >>>> Instead of showing up as a position error, they show up as an error
> in the
> >>>> time estimate. Since time is one of the things you estimate in the
> >>>> solution
> >>>> (along with X,Y, and Z) it get’s it’s own independent solution.
> >>>>> Q2: Why have I not seen this issue raised in connection with the
> present
> >>>>> discussion
> >>>>>      about achievable absolute timing accuracy?
> >>>> GPS time transfer is often done to the sub-ns level. There are a
> number of
> >>>> papers on this.
> >>>>
> >>>>> Q3: Do any of the "modern" timing GPS receivers available to
> civilians do
> >>>>> dual-band
> >>>>>      reception in a way that includes estimation of (and correction
> for)
> >>>>> said delays and
> >>>>>      their variations?  I know that Garmin, for one, is now selling
> L1/L5
> >>>>> handheld GPS
> >>>>>      receivers (GPSMAP66sr and GPSMAP65s), but I've seen no
> indication
> >>>>> that these
> >>>>>      units make any attempt at doing such corrections.
> >>>> Yes, some receivers do an estimate of ionospheric delay based on the
> >>>> variation of that delay with frequency. This does not help with
> >>>> tropospheric
> >>>> delay or all of the various “common mode” issues we have been talking
> >>>> about.
> >>>> It is also unclear how the “unknown” timing variation between the
> bands
> >>>> due to the antenna impacts these solutions…..
> >>>>
> >>>> Bob
> >>>>
> >>>>> Dana
> >>>>>
> >>>>>
> >>>>>
> >>>>> On Sat, Feb 27, 2021 at 7:43 AM Bob kb8tq<kb8tq at n1k.org>  wrote:
> >>>>>
> >>>>>> Hi
> >>>>>>
> >>>>>> The same 20 or so ns delay in a saw would also apply to the
> >>>>>> saw (or tight filter) in some timing antennas. It also would apply
> >>>>>> to the saw(s) in some modules. Even if the tolerance is “only”
> >>>>>> a couple ns on each of them, you *could* have 3 or more in the
> >>>>>> chain.
> >>>>>>
> >>>>>> Lots of numbers to crunch to get to 5 ns “absolute”. One could go
> >>>>>> grab a GPS simulator and start poking. First step would be to find
> >>>>>> a simulator that is spec’d for a < 5 ns tolerance on the PPS into
> >>>>>> GPS out. I do believe that rules out the eBay marvels that some
> >>>>>> of us have lying around …..
> >>>>>>
> >>>>>> Simpler answer would be a quick “clock trip” with your car full
> >>>>>> of 5071’s …… hour drive over to NIST and then back home.
> >>>>>> That sounds practical for most of us :) :)
> >>>>>>
> >>>>>> Bob
> >>>>>>
> >>>>>>> On Feb 26, 2021, at 9:29 PM, John Ackermann N8UR<jra at febo.com>
> wrote:
> >>>>>>>
> >>>>>>> A while ago I tried doing a decidedly non-anechoic measurement
> with a
> >>>>>> VNA exciter going to a 1500 MHz ground plane and the receiver
> connected
> >>>> to
> >>>>>> the antenna (with a known delay cable) and I got a similar result,
> but
> >>>>>> there was enough noise that I didn't think I could nail it down to
> >>>> within
> >>>>>> 10 ns.
> >>>>>>> I've also measured GPS antenna splitters and they tend to have
> 20-ish
> >>>> ns
> >>>>>> delays, mainly due to the SAW filters.  I did surgery on an HP
> splitter
> >>>> to
> >>>>>> remove the filters so it could be used for L1 and L2 and that
> dropped
> >>>> the
> >>>>>> delay down to only 1 or 2 ns.
> >>>>>>> So there's definitely lots of stuff to calibrate if you want to get
> >>>>>> accurate time transfer.
> >>>>>>> John
> >>>>>>> ----
> >>>>>>>
> >>>>>>> On 2/26/21 8:02 PM, Michael Wouters wrote:
> >>>>>>>> Typical L1 antenna delays range from 20 to 70 ns.
> >>>>>>>> I know of only one antenna for which a delay is given by the
> vendor
> >>>> and
> >>>>>> the
> >>>>>>>> technique used was just to measure the electronic delay ie by
> >>>> injecting
> >>>>>> a
> >>>>>>>> signal into the circuit. To do it properly, you need a setup in a
> >>>>>> microwave
> >>>>>>>> anechoic chamber with transmitting antenna etc. The practical
> >>>> difference
> >>>>>>>> may be small though, 1 or 2 ns ( sample of one antenna!).
> >>>>>>>> Cheers
> >>>>>>>> Michael
> >>>>>>>> On Sat, 27 Feb 2021 at 11:42 am, John Ackermann N8UR<jra at febo.com
> >
> >>>>>> wrote:
> >>>>>>>>> They're claiming "even better than" 5 ns for relative time, which
> >>>> given
> >>>>>>>>> the 4 ns jitter seems at least sort-of reasonable.  But until
> someone
> >>>>>>>>> shows me otherwise, I'm still thinking that getting better than
> 25 ns
> >>>>>>>>> absolute accuracy is a pretty good day's work.
> >>>>>>>>>
> >>>>>>>>> John
> >>>>>>>>> ----
> >>>>>>>>>
> >>>>>>>>> On 2/26/21 5:26 PM, Bob kb8tq wrote:
> >>>>>>>>>> Hi
> >>>>>>>>>>
> >>>>>>>>>> I can’t think of many antennas (multi band or single band) that
> >>>> claim
> >>>>>> to
> >>>>>>>>> know their
> >>>>>>>>>> delay to < 5 ns. Simply having a *differential* delay spec of <
> 5 ns
> >>>>>> is
> >>>>>>>>> quite good.
> >>>>>>>>>> Same thing with delay ripple, you see specs out to around 15 ns
> on a
> >>>>>> lot
> >>>>>>>>> of antennas.
> >>>>>>>>>> None of this is getting you to the actual total delay of the
> >>>> antenna.
> >>>>>>>>> It’s a pretty good
> >>>>>>>>>> bet that number is a bit larger than either of these.
> >>>>>>>>>>
> >>>>>>>>>> Some of the ripple probably comes out in the standard modeling.
> I’m
> >>>>>> not
> >>>>>>>>> sure that
> >>>>>>>>>> the differential delay is taken out that way. Total delay, not
> taken
> >>>>>> out
> >>>>>>>>> in any obvious
> >>>>>>>>>> fashion ( at least that I can see). If the F9 has a built in
> antenna
> >>>>>>>>> database, that’s not
> >>>>>>>>>> mentioned in the doc’s. Any benefit from the corrections would
> have
> >>>> to
> >>>>>>>>> be part of
> >>>>>>>>>> post processing.
> >>>>>>>>>>
> >>>>>>>>>> No, that’s not the same as talking about the F9 it’s self doing
> X
> >>>> ns,
> >>>>>>>>> but it would be part
> >>>>>>>>>> of any practical system trying to get close to 5 ns absolute
> >>>> accuracy.
> >>>>>>>>>> 5 ns *relative* accuracy between two F9’s? I probably could buy
> that
> >>>>>> if
> >>>>>>>>> the appropriate
> >>>>>>>>>> one sigma / on a clear day / with the wind in the right
> direction
> >>>> sort
> >>>>>>>>> of qualifiers are
> >>>>>>>>>> attached.
> >>>>>>>>>>
> >>>>>>>>>> Bob
> >>>>>>>>>>
> >>>>>>>>>>> On Feb 26, 2021, at 4:27 PM, John Ackermann N8UR<jra at febo.com>
> >>>>>> wrote:
> >>>>>>>>>>> It's interesting that they talk about the F9 receivers
> offering 5
> >>>> ns
> >>>>>>>>> absolute time accuracy.  Does anyone know of tests confirming
> that,
> >>>> and
> >>>>>>>>> what sort of care was required in the setup to get there?
> >>>>>>>>>>> John
> >>>>>>>>>>> ----
> >>>>>>>>>>>
> >>>>>>>>>>> On 2/26/21 9:34 AM, Robert LaJeunesse wrote:
> >>>>>>>>>>>> FWIW. No detailed content, and a rather quick read. "Five key
> >>>> trends
> >>>>>>>>> in GPS".
> >>>>>>>>>>>> https://www.u-blox.com/en/blogs/insights/five-key-trends-gps
> >>>>>>>>>>>> _______________________________________________
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> --
>
> Jim Muehlberg
> Senior Engineer
>
> National Radio Astronomy Observatory
> ngVLA Local Oscillator Lead
>
> 1180 Boxwood Estates Rd B-111
> Charlottesville, VA 22903-4602
> P 434.296.0270
> C 434.422.2017
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