[time-nuts] Advice on good reception for radio clocks

Kasper Pedersen time-nuts at kasperkp.dk
Wed Jun 27 15:59:13 UTC 2012


On 06/27/2012 04:04 PM, Tony Finch wrote:

> Are there any basic steps I should take to improve the reception quality
> of a radio clock? I have a cheap and cheerful DCF77 receiver for
> connecting to some GPIO pins, but its PPS output is basically noise with
> maybe a one-second period. Perhaps it's just cheap and nasty.
> 


Be careful what you connect the ground of the receiver to.

When I did my DCF77 receiver, my first source of interference was the
common noise on the output of the supply I was powering it off of.
I went to a linear power supply, and things were good for a few years.

Then they installed remote-reading power meters in the neighbourhood,
and DCF77 was completely jammed. The meters talk back on 75kHz with
~6kHz bandwidth. Halfway by accident I found out that if I earth the
receiver well enough, thereby shunting off some of the 75kHz common mode
signal, I get mostly reliable reception all day.

I would suggest, at least for development, a battery and an optocoupler
to isolate the receiver section from conducted interference.

Hmm, I do have a Pi.
And when you have trouble decoding the signal at around 04 in the
morning, you too will have rediscovered sferics, and the need for a
filter that handles that.

/Kasper Pedersen



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