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

[paul swed]

I guess I would ask what the goal of the effort might be.
It seems like a good answer. One thing I was amazed buy was that back in
the 1960s HP wrote some papers on using WWVB. What they did was check the
offset at distance everyday about the same time. This offered quite a bit
more accuracy and avoided all of the night propagation effects. Essentially
from day to day the path is about the same.
If your system is stable enough could you simply put it in holdover at
night?
The other question I had is how do you then use the locked crystal
oscillator at 5.184 Mhz?
Does it somehow divide down to a useful number?
Nice project and good luck. Looking forward to hearing more.
Regards
Paul
WB8TSL

On Fri, Jan 15, 2021 at 11:02 AM JF PICARD via time-nuts <
time-nuts at lists.febo.com> wrote:

>  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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