primary and auxiliary systems can be tied together at various
switchboards, or individual stations may be cut out of the
circuits; but the supplementary system does not have these
Circuits in the supplementary system are usually not manned.
Some supplementary circuits are equipped with a buzzer or a
horn for calling another station. The supplementary circuit you
will use the most is the call signal station (fig. 3-6). To call
another station, you turn the station selector switch to the station
you want to call and then turn the hand crank. The hand crank
operates a magneto generator that produces a distinctive howl (an
audible noise). The howl will continue as long as you crank the
How do you call another station from a call signal
Figure 3-6.A call signal station.