SOUTHERN AVIONICS COMPANY
Model SA100 Dual
2-77
Theory of Operation, Radiobeacon
transmission over radio or telephone link. The Modem PWB supplies this data conversion. U1 of
the Modem PWB is a single package modulator-demodulator integrated circuit which converts
the data stream to an audio channel with frequencies of 2025 Hz and 2225 Hz for transmission
from the transmitter to the Remote Control Panel. Control switch positions are transmitted from
the Remote Control Panel to the transmitter site over a second audio channel with frequencies of
1070 Hz and 1270 Hz. The two audio channels are electrically separated. To program a modem
for use in the Local Control Panel, remove Jumper J1 from the Modem Board if it has been
previously installed. Install Jumper J1 for use of the modem in the Remote Radiobeacon Control
Panel. U1 detects the presence or absence of an audio carrier transmitted from the modem
located at the other end of the data link. A carrier detect LED is located on the Modem Board for
diagnostic purposes. It will remain lit whenever a carrier of the proper frequency channel is
received.
Summary of Contents for SA100
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