b. Keying the intercom. To key the intercom (ENERGIZE THE RELAYS), a
circuit to ground must be completed by keying (PUSH-TO-TALK) the audio
accessory (Figure 6).
When the audio accessory is connected to J803, the
intercom can be keyed with the MONITOR switch on the C-2298, set to any
position. When the audio accessory is connected to J802, the intercom can
be keyed only when the MONITOR switch is set to INT ONLY.
(1) When keying the intercom from the commander's (CDR) C-2298 J803,
a ground is being applied through the handset to the 22-30 volts DC at J803,
pin C. Current flows through the circuit, which causes each K501, K502, and
K503 to energize, keying the AM-1780.
(Trace this circuit on your system
Commander's intercom keying circuit (intercom keyed).