Although simple jammers have been around as long as radio transceivers have, technological advances of the past decade has thrusted forward the development of advanced and sophisticated intelligent jamming equipment. Early jammers were but a simple transmitter keyed on to a specific frequency producing a carrier which interfered with receiving stations. Modern day ECCM radio equipment use such techniques as Frequency Hopping and Spread Spectrum technology to circumvent the effects of ECM jamming equipment. Modern technology has lead to the development of modern jamming equipment employed in today's tactical environment. This new breed of equipment is capable of employing such techniques as wide-band rf spectrum transmitters, and various audio tones to jam or to spoof receiving equipment and their operators.
Most jammers feature several modes of operation and several modulation types.
Operational modes range from hand keying, random keying, periodic keying, continuous keying and the more sophisticated look through mode. A CW jamming signal beats with another signal and produces a steady tone. In the case of SSB or AM signals a howl sound is produced at the receiving station. When various types of modulations are applied to a transmitter, this is referred to as Modulated Jamming . Below are some modulation samples to aid in the recognition of jammer signals.