[time-nuts] lawnmower robots may be the end of VLF timekeeping

Esa Heikkinen tn1ajb at nic.fi
Sat May 9 15:10:51 EDT 2015


Poul-Henning Kamp kirjoitti:

> I spent some time capturing some data today.
> The measurements is from my $20 loop-antenna in the attic, which is
> something like 8 meters up and 10 meters besides the lawn-mower loop:
> 	http://phk.freebsd.dk/time/20150509.html

In the Finland that problem is even worse! For me it's called Savon 
Voima, our local power company (but also many other power companies 
around the Finland). They are using PLC based remote readable utility 
meters. These meters communicate with power lines, using ancient 1200 
bps. FSK using 83.2/93.6 kHz frequencies. Because the power grid is not 
designed for this kind of communication, those frequencies will of 
course leak all over the places.

Because the metering hardware is cheap crap made by Slovenian company, 
those frequencies are not very accurate/narrow and so they block the 
DCF77 77,5 kHz band totally! Because all in-house wiring act as an 
transmitter antennas, the field strenghts inside the houses can be as 
high as 120 dBuV/m.

The system is so stupid that it need to communicate 24h to transfer less 
than six digits (the reading of the utility meter), which is basicly 
needed once per month for elecricity billing. Every meter can act as 
repeater to other meters.

The DCF77 problem was verified when there was large blackout. During 
this blackout the DCF77 clocks was syncronized at moments, when they 
never synchronize normally.

When this was reported to Finnish authority called Viestintävirasto 
(it's Finnish version of FCC), they say that this doesn't matter - the 
DCF77 is not "protected" in Finland (even when you can buy radio 
controlled clocks from the shop).

The whole idea about PLC is so stupid and the universal stupidity factor 
of the people designing these is so high that there's nothing to do 
anymore. Even the power company said that this is not reliable system, 
having much of interferences, the readings are not transferred 
succesfully all the times. But still they buy this kind of crap, even 
when knowing it weaknesses. Clearly the marketing guys of PLC systems 
knows their business and they can even cope with local auhorities so 
that there's no problems to install these everywhere.

I think that we have lost the game! Only way to set the clock is to 
build your own DCF77 transmitter - like the local authority said: the 
DCF77 band is not "protected" - at least here in Finland...

-- 
73s!
Esa
OH4KJU



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