A random interesting observation by my radio clocks:
Normally the DCF77 transmitter uses a mechanism that shifts the transmitter phase by steps of 100ns. There's an observation receiver somewhere (don't know where) that receives the transmitted signal and the transmitter phase gets adjusted by said 100ns steps to compensate for whatever happens on the way from the transmitter through the antenna.
Normally this behaviour looks like some random phase noise superposed to the phase of the received signal, like this:
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1224511;image)
The phase has steps of nominally 2.79 degrees every few seconds.
This morning, the signal looked like this:
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1224513;image)
No steps, just noise. I've seen this before, it's rather rare. I don't know if the phase correction just isn't necessary or if someone turned off this control loop by intention.
I've noticed this (the 2.79° steps) when I tested my radio clock for the first time and was curious about it - is this some kind of secret data transmission? So I just asked the folks at PTB and got an answer, explaining this control system, which matched exactly my observation. At the time I've asked them, it wasn't documented on their public website.