Computing stuff tied to the physical world

Microwave interference?

In Hardware on Nov 15, 2012 at 00:01

To get more options with remote nodes, I wanted to get this DCF77 clock working again, broadcasting the current time of day once a minute:

3311819588 20f3b58d12 o

Last time I tried (long ago), it didn’t work – but I’ve been running the OOK Relay for ages now, and since it still had the DCF77 receiver hooked up, I decided to have another go.

Sure enough – all it was is a broken wire… doh!

Now there are time-of-day packets in the air again, here at JeeLabs – sent by ookRelay2:

Screen Shot 2012 11 13 at 12 24 29

It works really well – at last – and will come in handy soon enough, I expect.

But the curious thing is those 3 missed packets at 12:13, 12:16, and 12:19.

Could it be the microwave? It was just around the time I was heating up something…

More investigation needed.

  1. But.. the DCF77 signal is 77(.5) kHz, which is well outside the range of the microwave? Interesting. :)

    • Indeed – it may also be some fluorescent lights. Or the induction stove? Hopefully with more data the cause will become clear.

  2. Noise can get wrapped onto a certain band in an electrical system under a lot of different conditions. If your receiver doesn’t contain a filter it wouldn’t surprise me if that happens here too. Wireless headphones are another nice example, because most of them are way outside of the microwave band, but will still have trouble receiving the signal if a microwave is on nearby. The same thing goes for some wireless networks etc.

  3. I recently found that in our living room a 12V/2A switching power supply loaded with about 8 Watts of LED stripes and mounted behind a wood board inhibits DCF77 reception for the radio clock that hangs on the front side of the board.

    Fortunately the LEDs are usually off at night when the clock resynchronizes with DCF77, but the morning after I was up late following the US election, my daughter noticed that the radio symbol was gone from the clock’s display. Further investigation revealed it was the power supply I had installed a few days earlier.

  4. One hopje bet that it is the induction hob. Especially on “low heat”, they can generate RF “hash” well into the MHz. A mains line filter can sometimes damp it down, but those coils under the ceramic surface are hard to shield.

    • Right on the button – as always – I suspect: yesterday evening the clock packets were gone for long periods of time, and it did indeed coincide with Liesbeth preparing a wonderful meal! Good – I’m logging both, so it should be possible to bring out the correlation once enough data has been collected. Hopefully it only disturbs the DCF77, not the 868 MHz packets flying around here all the time.

Comments are closed.