On 2016-11-29 19:30, Jeff Liebermann wrote:
On Tue, 29 Nov 2016 18:07:29 +0100, "Carlos E.R."
wrote:

And I hope it is well built... I have a wall clock that syncs every
night (about 3 AM) from a radio signal from Germany, I think. The rest
of the day it runs autonomously.

I'm surprised that it works. I think you're in Spain and DFC77
transmitter is in Germany. Spain is at the outer edge of the coverage
area:
https://en.wikipedia.org/wiki/DCF77#Reception_area
https://en.wikipedia.org/wiki/DCF77#/media/Filecf_weite.jpg

Yes, I am at the middle of the 1500 km circle. Ie, at something like
1700 km. Those clocks are widely sold here, but they don't work on every
room. Your graph explains it, but I already suspected it.

Pity there are no nearer transmitters. A network of transmitters, probably.

You can improve reception by moving the clock to a location where
there is less electrical interference (away from switching power
supplies, TV's, computahs, etc). Also, orienting the loopstick so
that it is horizontal and "broadside" to the direction of Germany.


My clocks (I have 4) do not have a ferrite rod, like those in the
wikipedia. Unless minimal and well hidden.

However, sometimes there is some problem and it is 15 hours off sync.

That's what happens when the clock receives garbage instead of an
update. The usual algorithm is for the clock to receive two or three
valid updates in close succession before it will accept the data. If
it hears two identical noisy updates, it will display erroneous data.
It's very unlikely that this will happen, but it's not impossible. If
your clock does NOT require two or three consecutive valid updates,
it's highly likely that you will see far more garbage updates.

I guess all use the same chip, and it is faulty. Once the clock syncs
well, it should reject an update that is more than some minutes off.
Humm... but then there is the summer saving time change. But some clocks
use 3 volts instead of 1.5 and work better.


Depending on the model, it can manage to sync the next day, or never. I
can not really trust it.

I don't think a DFC77 clock will work reliably at your location in
Spain. Think about using NTP updates from over the internet instead.

I thought about that, yes, but not how to do it cheaply. A tablet would
do, but more expensive.

It can easily be done with a Raspberry Pi.
http://www.satsignal.eu/raspberry-pi/DigitalClock.html

Interesting, but complicated.

An old handheld GPS receiver, mounted on the wall will also work but
watch out for the 17 sec the GPS - UTC difference.

:-)

--
Cheers, Carlos.