The Appearance of Jamming

Some cell phone jammers are made to look like actual phones. Others are briefcase-sized or larger.
The biggest cell phone signal jammers used by police and the military can be mounted in vehicles for convoy security.
Inside Cell Phone blocker.
Electronically speaking, 3g4g cell phone jammers are very basic devices. The simplest just have an on/off switch and a light that indicates it's on. More complex devices have switches to activate jamming at different frequencies. Components of a jammer include:

Antenna

Every jamming device has an antenna to send the signal. Some are contained within an electrical cabinet. On stronger devices, antennas are external to provide longer range and may be tuned for individual frequencies.

Circuitry

The main electronic components of a mobile phone blocker are:
  • Voltage-controlled oscillator - Generates the radio signal that will interfere with the cell phone signal
  • Tuning circuit - Controls the frequency at which the jammer broadcasts its signal by sending a particular voltage to the oscillator
  • Noise generator - Produces random electronic output in a specified frequency range to jam the cell-phone network signal (part of the tuning circuit)
  • RF amplification (gain stage) - Boosts the power of the radio frequency output to high enough levels to jam a signal