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

paul swed paulswedb at gmail.com
Tue Oct 11 13:30:23 UTC 2022 

With respect to the bad units I believe in West Virginia there are parts
that I could use to keep my old 5061s cooking. The small HV supplies and
the RF multiplier assembly. Essentially the waveguide structure that
attaches to the tube.
With respect to the tubes I have also recovered one that was dead. Good or
bad I created a new DC oven controller and ran the CS hotter. With humor
only later did I learn that HP made a DC oven controller. Hey have fun with
those dead tubes. It doesn't hurt.
Regards
Paul
WB8TSL

On Tue, Oct 11, 2022 at 2:57 AM Aiden Gibson via time-nuts <
time-nuts at lists.febo.com> 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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