Garmin G1000 Cockpit Reference Guide for Cessna Nav III 65SECTION 4 – AUDIO PANELMarker Beacon ReceiverThe GMA 1347 marker beacon is used as part of theILS system. The marker beacon receiver is always ON andreceives at 75 MHz. The GMA 1347 provides a markeraudio muting capability.The receiver detects the three (3) marker tones, outer,middle and inner, and illuminates the appropriate mark-er beacon indicators. The marker indicators are locatedto the left of the altimeter on the PFD (Figure 4-4). Theouter marker frequency is 400 Hz with a blue indicator,the middle marker frequency is 1,300 Hz with an am-ber indicator and the inner marker frequency is 3,000 Hzwith a white indicator. Refer to Table 4-1 for a summaryof the marker beacon signal characteristics.When the MKR/MUTE key is selected, the annuncia-tor light becomes illuminated and the audio signal can beheard over the speaker or headsets during marker recep-tion.When the MKR/MUTE key is annunciated and a mark-er beacon tone is received, pressing the MKR/MUTE keymutes the audio but does not affect the annunciators. Theaudio returns when the next marker signal is received. Ifthe MKR/MUTE key is pressed during signal reception,while marker beacon audio is muted, marker audio andthe MKR/MUTE key annunciator light are turned off.NOTE: The marker beacon receiver lights operateindependently of the marker beacon audio andcannot be turned off.Marker Beacon Signal SensitivityThe HI SENS key can be pressed for increased markerbeacon signal sensitivity. The HI SENS function is usedto receive an earlier indication of nearing a marker duringan approach.Figure 4-3 Marker BeaconThe lamp and audio keying of the marker beacon re-ceiver are summarized in Table 4-1.
