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

Tue Oct 11 15:39:58 UTC 2022

Lester absolutely true you could lock to a GPS. Save me the rf multiplier
that you won't be needing. Now the good news is that the tube and such will
reduce the weight quite a bit. The 5061s are heavy...
The 5061 should give you a 1 pps out and then any number of GPSDO circuits
out there can do the rest of the job.
Happy to discuss further and Time-nuts is the right place for the
discussion.
Regards
Paul

On Tue, Oct 11, 2022 at 11:19 AM Lester Veenstra via time-nuts <
time-nuts at lists.febo.com> wrote:

> They will look good in the rack next to the Sulzer and HP Crystals, the
> Rubidium, and the ex telco GPS and the Chinese GPS.  I probably could
> discipline the internal 5 MHz to an external GPS
>
> Lester B Veenstra  K1YCM  MÃ˜YCM  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: Bob kb8tq [mailto:kb8tq at n1k.org]
> Sent: Monday, October 10, 2022 4:46 PM
> To: Discussion of precise time and frequency measurement
> Cc: Lester Veenstra
> Subject: Re: [time-nuts] HP atomic clocks . The cesium tubes in them are
> no longer any good,
>
> Hi
>
> Iâ€™d guess there are at least 5 chassis out there for every fully
> functional
> HP tube, at least if you are talking about the stuff that came out before
> the
> 5071A. It probably still is 5 or more chassis, even if you count
> semi-functional
> tubes. There are ways to swap around tubes between brands. Even so, there
> still arenâ€™t many good tubes to go around.
>
> All that said, one should never turn down an offer like this. You just
> never
> know what might suddenly turn up tomorrow :)
>
> Bob
>
> > On Oct 10, 2022, at 10:50 AM, Lester Veenstra via time-nuts <
> time-nuts at lists.febo.com> wrote:
> >
> > Wrong email subject on original post, Apologies
> >
> > Lester B Veenstra  K1YCM  MÃ˜YCM  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  MÃ˜YCM  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 â€œdelay is equal in both directionsâ€ 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 Allanâ€™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 â€œhitâ€ 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 getâ€™s itâ€™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 â€œcommon modeâ€ issues we have been talking
> >>> about.
> >>> It is also unclear how the â€œunknownâ€ timing variation between the bands
> >>> due to the antenna impacts these solutionsâ€¦..
> >>>
> >>> 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 â€œonlyâ€
> >>>>> 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 â€œabsoluteâ€. One could go
> >>>>> grab a GPS simulator and start poking. First step would be to find
> >>>>> a simulator that is specâ€™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 â€¦..
> >>>>>
> >>>>> Simpler answer would be a quick â€œclock tripâ€ with your car full
> >>>>> of 5071â€™s â€¦â€¦ 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 canâ€™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.
> >>>>>>>> Itâ€™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.
> Iâ€™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, thatâ€™s not
> >>>>>>>>> mentioned in the docâ€™s. Any benefit from the corrections would
> have
> >>> to
> >>>>>>>> be part of
> >>>>>>>>> post processing.
> >>>>>>>>>
> >>>>>>>>> No, thatâ€™s not the same as talking about the F9 itâ€™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 F9â€™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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