text: Appendix A
  Table A-1. Common jamming signals
  Signal Description
  Random Synthetic radio noise. It is indiscriminate in amplitude and frequency. It is similar to normal
  Noise background noise and can degrade all types of signals. Operators often mistake random noise
  jamming for receiver or atmospheric noise and fail to take appropriate electronic protection
  actions.
  Stepped Tones transmitted in increasing and decreasing pitch. They resemble the sound of bagpipes.
  Tones Stepped tones are effective against single-channel amplitude modulation or frequency
  modulation voice circuits.
  Spark Bursts are of short duration and high intensity; they are repeated at a rapid rate. This signal is
  effective in disrupting all types of radio communications. Spark jamming is easy to produce and
  one of the most effective jamming signals.
  Gulls Quickly rising and slowly falling variable radio frequency. The effect produced is similar to the cry
  of a seagull. Gulls produce a nuisance effect and are very effective against voice radio
  communications.
  Random Pulses of varying amplitude, duration, and rate. Pulses disrupt teletypewriter, radar, and various
  Pulse data transmission systems.
  Wobbler A single frequency, modulated by a low and slowly varying tone. The result is a howling sound
  that causes a nuisance effect on voice radio communications.
  Recorded Any audible sound, especially of a variable nature. Recorded sounds can distract radio
  Sounds operators and disrupt communications. Music, screams, applause, whistles, machinery noise,
  and laughter are examples.
  Preamble A tone resembling the synchronization preamble of the speech security equipment, broadcast
  Jamming over the operating frequency of secure radio sets. Results in all radios being locked in the
  receive mode. Preamble jamming is especially effective when employed against radio networks
  that use speech security devices.
  Preventive Measures
  A-29. Measures operators and planners can use to reduce susceptibility to enemy jamming include—
  * Minimize radio transmissions. Try to keep radio transmissions to six seconds or less.
  * Use electronic counter-countermeasures, such as frequency hopping.
  * Train using radio silence.
  * Use low power setting on radios for normal operations to reduce the probability of detection.
  * Use terrain masking to reduce the probability of detection and block potential sources of enemy
  jamming.
  Indicators
  A-30. The enemy strives to perfect and use new and more confusing forms of jamming, which requires radio
  operators to be increasingly alert to the possibility of jamming. Training and experience allow operators to
  determine whether a particular signal is a jamming signal. During operations, radio operators should remain
  alert to possible jamming indicators. Observable indications of jamming include—
  * Apparently random noise or static over voice channels.
  * Recorded sounds—messages or music—over voice channels.
  * No answer to a radio transmission.
  Reaction
  A-31. Communications jamming requires prompt corrective action to restore critical communications
  capabilities. Possible reactions to jamming include—