This is a single frequency modulated by a slowly
varying tone resembling a howling sound. It is a nuisance to voice radio
(g) Preamble jamming. This is the broadcasting of synchronization
tones over the operating frequency of a radio net that uses voice security
devices. It often causes radios to be locked in the RECEIVE mode.
(h) Recorded sounds. These can be any audible sound of a varying
nature. Examples are music, screams, applause, whistles, machinery noise,
and laughter. They are used to distract voice radio operators and disrupt
(2) Subtle jamming is not obvious to the radio operator because no
sound is heard. The receivers are blocked and unable to receive an incoming
signal, even though everything seems normal.
Subtle jamming affects the
squelch mode of FM radios. It places a tone on the receiver squelch circuit
that blocks out weaker signals on the frequency. The operator believes the
radio is functioning properly, but no signal is present on the assigned
Atmospheric conditions, malfunctions of the radio, and other radios (enemy
or friendly) cause it.
Other sources include electric, electronic and
b. Once you realize an enemy is conducting jamming operations, you
should report the jamming. You should then:
(1) Continue to operate.
(2) Improve the signal-to-jamming ratio.
(3) Adjust the receiver. This includes adjusting the beat frequency
oscillator, adjusting the bandwidth, adjusting the gain or volume control,
and fine tuning the frequency.
(5) Adjust, change, or move the antenna.
(6) Set up a retransmission station.
(7) Change the frequency.
(8) Use a different satellite.