I am not an expert but this is how I understand it.

Originally they were designed to stop radar. They do this by detecting and broadcasting the same frequency and pattern back to the source. This can confuse the radar system that relies on bounced back signals from hard objects. Radar can work for more than 100 miles detecting very faint bounced back signals.

Newer ones (like the one destroyed) are designed to jam cell phone signals etc. This gets a bit more complicated. These are two way signals with both sources producing and receiving signals. Military ones are also encrypted to reduce jammers spoofing their signals. These types of jammers rely on producing lots of noise in the key frequencies that overpowers and masks the communication signals. Since radio signals follow the inverse-square law the jammers effective range is limited. For example an effective interference signal at 2 miles away from the source will be reduced by 75% at 4 miles away and likely be ineffective.