Hello, Lastly, I built a WiFi Jammer for all channels and then have this nicely installed in a case … This time I would somehow build a 4G LTE jammer. However, I have no plan how to do this now? Unfortunately, you will not find much on the internet either. PS … I am aware of the illegal consequences.
From a legal point of view, I can only advise against it. WLAN interference may still be reasonably OK (if, of course, already unauthorized), because it is an open frequency band and you probably have taken any allowed wireless module, which is then limited by the local broadcasting strength. The detectability should be correspondingly difficult (also that it is deliberate). At LTE, that could be something else. Incidentally, the Federal Network Agency has measuring stations distributed throughout Germany that monitor the radio room. If something strange comes up, you could be located.
Otherwise, you need a radio transmitter, usually software-defined radios (SDR) are used. A relatively inexpensive (300 €) is e.g. the hackrf. With enough transmission power, you may already bother something, it is better, of course, to deal with it more closely. For example modulation type, possible pilot tones, structure of the data packets … It should be noted, of course, that each network provider has its own frequency ranges. You will not be able to bother several (at least with such low-cost hardware) at the same time.