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

Fri Jan 15 23:22:57 UTC 2021

Sorry, forgot to include the cite:
LATHAM, D. Diurnal Frequency Variation and Refraction Index. Nature 
Physical Science 234, 157–158 (1971). 
https://doi.org/10.1038/physci234157a0

Don

On 2021-01-15 15:13, Andy Talbot 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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