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

Fri Jan 15 23:18:03 UTC 2021

What was the program that you used for the plot please?
Regards
Paul
WB8TSL

On Fri, Jan 15, 2021 at 5:54 PM Andy Talbot <andy.g4jnt at gmail.com> wrote:

> 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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