Unknown 433 MHz signal every 5 seconds for 30-40 ms

[joan]

I have a 433 MHz receiver connected to the Pi.

I am experimenting with removing static so ignore all signals if they have not been preceded by 30 ms (or thereabouts) of no high/low change.

I expected to get zero or random triggers.

I am getting a trigger every 5 seconds.

Is there a signal at this period on 433 MHz? It may be an artefact with my software, my initial tests suggest not.

[fruit-uk]

Someone, a neighbour perhaps, has got an energy monitor (Owl) or something similar?

[scruss]

What kind of 433 MHz receiver are you using? Most of the simple ones have a crude AGC circuit that ramps up the gain slowly until you get a trigger. This allows them to pick up faint signal, but also limits them to very short transmissions with fairly lengthy alternating 'training bits' headers.

I found rigging up a very tiny speaker element between the receiver's output and ground helped me tell if it was a regular signal or just noise.

[joan]

Thanks both.

I'm using the cheapest 433 MHz receiver I could find on eBay. It came as a RX/TX pair.

I'm not sure if the pulses after the 30-40 ms high edge are data or not. It's difficult to distinguish between static and signal. They may be a signal or any signal may be encoded in the length of the high edge (if I trigger on slightly longer edges I get regular messages at different, but regular, intervals).

[fruit-uk]

Might placing it in a grounded bsicuit tin be enough to block external signals?

[joan]

Might placing it in a grounded bsicuit tin be enough to block external signals?

That's where I keep my head apart from when outside when I use my rather fetching tin foil hat.

My real motivation is to discover if this is an artefact of my software or a real signal. It doesn't actually cause me any problems.