IFH 2-2

Figure 2-2. Audio panel. Figure 2-1. Typical navigation/communication installation. Communication Equipment Navigation/Communication Equipment Civilian pilots communicate with ATC on frequencies in the very high frequency (VHF) range between 118.000 and 136.975 MHz. To derive full benefit from the ATC system, radios capable of 25 kHz spacing are required (e.g., 134.500, 134.575, 134.600). If ATC assigns a frequency that cannot be selected, ask for an alternative frequency. Figure 2-1 illustrates a typical radio panel installation consisting of a communications transceiver on the left and a navigational receiver on the right. Many radios allow the pilot to have one or more frequencies stored in memory and one frequency active for transmitting and receiving (called simplex operation). It is possible to communicate with some flight service stations (FSS) by transmitting on 122.1 MHz (selected on the communication radio) and receiving on a VHF omnidirectional range (VOR) frequency (selected on the navigation radio). This is called duplex operation. An audio panel allows a pilot to adjust the volume of the selected receiver(s) and to select the desired transmitter. [Figure 2-2] The audio panel has two positions for receiver selection, cabin speaker, and headphone (some units might have a center “OFF” position). Use of a hand-held microphone and the cabin speaker introduces the distraction of reaching for and hanging up the microphone. A headset with a boom microphone is recommended for clear communications. The microphone should be positioned close to the lips to reduce