In the Netherlands, we have clocks at train stations like on the one on the image below.
In order to get the time as precise as possible, the clocks read the time from the DCF77 signal. (As far as I know, for the sake of this question, let's say it is the case.) DCF77 is a longwave time signal from Germany used in mainland Europe.
My question is, how secure are these clocks?
What would happen if I would broadcast a completely other time on the same wavelength near such a clock? Would the time change?
Disclaimer: I'm absolutely not planning on doing this. (Otherwise, I would have found out myself.) I'm just curious about how secure these clocks are.