[time-nuts] Long Wave Radio-Frequency standard testing

Fri Jan 15 22:13:38 UTC 2021

I did a plot of the phase of the UK 198kHz longwave transmission to me, a
path of about 150km, compared against an HP5061A Caesium standard
N

early 24 hours duration, covering night time and day time propagation in
October.

You can observe the wild wandering of both phase and amplitude  during
night time due to skywave/groundwave interaction as the ionosphere shifts
around.

Plot also at
http://www.g4jnt.com/DropF/droitwichplot2a.bmp
if the attachment doesn't get through

[image: DroitwichPlot2a.bmp]
Andy
www.g4jnt.com

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On Fri, 15 Jan 2021 at 21:55, Gilles Clement <clemgill at gmail.com> wrote:

> Hi JF,
> DCF77 is more distant, less powerful and probably more polluted (77kHz).
> Anyhow I would probably not be able to measure better than 10e-11 with
> current setup (need a better reference)
> Indeed a good and stable phase lock was not easy to reach.
> I experienced the day and night huge differences (as documented in post)
> but nothing specific to phase shifts during sunrise or sunset.
> No big difficulties with the ferrite antenna and the receiver design
> either (thanks to good stuff from the old radio days probably).
> Found that magnetic field antenna (ie: ferrite) appeared much less
> sensitive to pollution than electric field antennas.
> Naturally bad experience with Led bulbs and vapor gas lamps. You have to
> chase them all and change to old filament lamps in and around the lab. No
> issues with computers though.
> What I found most challenging (and hence interesting) was the following :
> - Temperature control, high resolution and high stability (Crystal
> oscillator but also for the controller parts, ADC, DAC… )
> - PI loop stability (very tricky)
> - Matching theory with practice (still work in progress…!)
> - Understanding the logic and physics behind behaviors, the real root
> cause of problems,
> and especially why a « really clever » enhancement - more than often -
> actually leads to… performance degradation...
> Gilles.
>
>
>
> > Le 15 janv. 2021 à 16:57, JF PICARD via time-nuts <
> time-nuts at lists.febo.com> a écrit :
> >
> > Hi,
> > 800Kw according to the press release of ANFR. I doubt it is the best
> choice : DCF77 is more precise (active hydrogen maser) but a little bit
> more distant...
> > But the phase lock of a quartz on a VLF signal is not as easy. There is
> a considerable phase shift in the evening and in the morning with the sun
> position, big instabilities at these moments and you have a hudge
> difference between day and night (10 e-9/8)... Have a look at the Adret
> receiver 4101 with its step motor phase lock...The engineering of the
> ferrite road antenna is very tricky : temperature coefficient of the
> ferrite, subtle tiny out of resonnace tuning, problem of the interferences
> from domestic electrnic pollution (computers with sync of monitors, led
> drivers...). The archiyecture of the receiver is also tricky : no AGC
> (introduces phaseshift), heavy filtering (where : antenna, receiver...)
> >     On Friday, January 15, 2021, 03:54:40 PM GMT+1, Gilles Clement <
> clemgill at gmail.com> wrote:
> >
> > Hi,
> >
> > This is to share current results on a "Long Wave RadioFrequency
> Standard" project I have been pursuing for a while.
> > Attached are typical ADEV plots and a block diagram of the system.
> >
> > I live in a crowded city (Paris, France) with no - or very limited -
> access to open sky. Not good for GPS.
> > However a long wave broadcasting public service is (still) available,
> broadcasting time signal for clocks.
> > The transmitter is located in Allouis, central France (200km for Paris).
> > The signal is quite powerful (1MW) and the carrier (162kHz ) is
> stabilized with a Cesium-standard.
> >
> > I decided to test how far I could go in disciplining a local VCO with
> this signal.
> >
> > As well known, long wave RF has interesting features:
> > - Signal is available (almost) everywhere, anytime, in the country
> especially inside buildings (even underground !)
> > - Quite stable and strong ground wave in day time.
> > - Relatively easy antenna and RF signal processing (ferrite rod)
> > And there are naturally a number of drawbacks (especially with the
> Allouis signal) such as:
> > - Much more unstable signal at night (interferences with ionospheric
> path)
> > - Large phase modulation of the carrier (time signals bits +/- 1 rad
> phase modulated).
> > - RF perturbations on the signal path.
> > -Stop broadcasting for maintenance every Tuesday morning….
> >
> > Design of the « LWRFDO » was derived and inspired from many references
> (including this list naturally).
> > Principles are summarized in the attached pdf, with the following
> specific feature to get rid of the phase modulation:
> > The incoming signal has large sections of « un-modulated » segments
> between the time signal bits.
> > (Including a whole quiet section during the 59th second)
> > Such « quiet zones » are detected - where the 162kHz base carrier is
> untouched - and measurement of phase difference
> > with a local OCXO is then performed inside these quiet zones. Then PI
> controller to a 20bits DAC (see picture).
> >
> > Latest results show ADEV approaching 10E-11 at 1000 seconds on the « D2
> » graph (day time only).
> > « DN123 » is a three days uninterrupted run, combining day and night
> signals, showing the impact of night instabilities.
> > The frequency standard stability at the transmitter site  is given for
> 10e-12.
> > LWRFDO PPS is measured against an HP10811A PPS (about 10e-11 stability a
> 100s) with a TICC,
> > So I believe 10-11 is not far from the best one could get.
> > Which is actually not too bad, isn’t it ?
> >
> > Still working on improving the OCXCO (currently home brewed)
> >
> > Comment and suggestions welcomed,
> > Gilles.
> >
> >
> >
> >
> >
> >
> >
> >
> > _______________________________________________
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>
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