Ericsson EF738 Service Manual page 175

Technical Description
RX and TX Sat Circuits
RX SAT Filter
A 6 kHz bandpass filter is included to capture the received SAT tone from the com-
posite received audio signal
RX SAT Schmit Trigger
The filtered SAT signal is then amplified and routed to a schmit trigger circuit in
ANTON where it is squared up and driven to GUSTAV as a digital signal.
TX SAT Filter
The TX SAT signal originates in GUSTAV as a digital signal. The TX SAT filter is a
6 kHz bandpass filter for removal of high order harmonics from the signal.
TX SATDEV Programmable Gain Stage
A programmable gain stage SATDEV is provided to adjust tolerances in the sum-
ming circuit to maintain the proper signal level to transmit a 6 kHz SAT tone at 1.7
kHz FM deviation. This gain stage is nominally 0 dB with an adjustment range of
+4.8 to -4.5 dB in steps of 0.3 dB.
Test mode 22 can be used to adjust SATDEV.
8Kbit/s Manchester Data Circuit
Data Filter
A 20 kHz lowpass filter is provided to limit the frequency components of the digit-
ally generated Manchester data.
Data is transmitted as an 8 kHz signal at 6.2 kHz FM deviation.
DATADEV Programmable Gain Stage
The filtered data signal is routed to a programmable gain stage, DATADEV, for
trimming out tolerances in the summing amplifier. The DATADEV gain stage is
nominally 0 dB with an adjustment range of +3.2 to -2.8 dB with steps of 0.4 dB.
HandsFree Circuit
ANTON includes rectifier circuits for audio detection in the RX and TX paths.
A single port is provided for the monitoring of the rectified signal.
A switch is software controlled to select the RX or TX path for sampling.
An external capacitor is provided to set the time constant for each path.
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