I found that on the train my mobile phone often has no signal, can't talk, can't send messages, why is this?

I need to travel a lot for work reasons, so I often take the train. I found a problem that my mobile phone has no signal at all on the train several times, and my mobile phone can't even send messages, which makes me very distressed. , I wonder why this is?

Topsignaljammer  2022.

Hello, according to your statement, it is very likely that someone has used a cell phone jammer on the train. The cell phone signal jammer scans from the low-end frequency of the forward channel to the high-end frequency at a certain speed during the working process. The mobile phone manifests as the phenomenon of searching the network, no signal, no service system, etc.