MAJOR COMPONENTS

Figure 1-6-RT-1397/ARC-197 transceiver. In the P-3C aircraft, this system interfaces with four of the intercommunication stations in the transmit/receive functions. The pilot, copilot, TACCO, and NAV/COMM stations can transmit and receive over this radio. The other stations in the aircrafl have receive function only. MAJOR COMPONENTS There are three components to the AN/ARC-197 system. These components are the RT-1397/ARC-197 transceiver, the C-11067/ARC-197 VHF-AM control panel, and the 949880 VHF antenna. RT-1397/ARC-197 Transceiver The RT-1397/ARC-197 transceiver (fig. 1-6) is a solid-state unit, consisting of a power supply, frequency synthesizer, receiver modulator, and transmitter. There is one indicator, one push button, one microphone jack, and one headphone jack on the unit. The indicator is labeled TRANSMIT POWER, which illuminates when output power is greater than 10 watts. The push button is labeled SQUELCH DISABLE, which will disable the squelch for low signal levels. The microphone and headphone jacks are used for maintenance and emergency VHF communication in case of ICS failure in-flight. C-11067/ARC-197 VHF-AM Control Box The control box (fig. 1-7) controls the operation of the system. There are two dual function knobs and a display window on the control panel. The display window shows the selected frequency of the system. Figure 1-7.-VHF-AM control box. The outer ring of the dual function knob on the left applies system power and selects the test function. The inner knob changes the frequency of operation in 1-MHz steps over the range of control. The outer ring of the dual function switch on the right is labeled VOL, and it is not used in the P-3 aircraft. Volume is controlled by the ICS system. The inner knob of this control is used to change the frequency of operation in 25-kHz steps over the range of control. 949880 VHF Antenna The 949880 antenna is located in the tailcap on top of the vertical stabilizer of the P-3 aircraft. This antenna radiates and receives the VHF radio frequency signals. Signals routed to and from the antenna go through a VHF bandpass filter, which reduces the crosstalk between the VHF and UHF systems. VHF FUNCTIONAL DESCRIPTION There are two modes of operation with the AN/ARC- 197 radio. These two modes are receive and transmit. Receive Mode In the receive mode, the received RF signals from the antenna are routed through the filter, and applied to the receiver circuits in the transceiver. The frequency selected on the control box is applied to the frequency synthesizer. The synthesizer uses a single phase-locked loop to generate RF injection frequencies, in 25-kHz steps, from 116.000 to 155.975 MHz. The RF injection frequencies, along with dc tuning voltages, electronically tune the receiver to the selected frequency. The AM detected audio is applied to the audio amplifier circuit. Squelch circuits disable the output amplifier if the required signal-to-noise ratio or carrier level is not present. The output audio is then applied to the ICS interconnection box for distribution to the various stations. 1-12