SIGMA BENEFON TDP-52-SN3 - Manual (Page 45)

27.1.1999
4A0701GB.__1 11
Product: TDP-52-SN3 (Sigma Gold) / OA0700 Audio
transmit signal. VR3 is a maximum deviation gain control circuit to set the
transmit signal level. After the VR3 comes switch TXAUDON, which mutes the
tx-audio signal using the TXMUTE control. From the switch, the signal is fed to
the summing junction (ADD3) of the tx-audio signal, FFSK signal and Fii-
signal. Next comes VR4 gain control circuit to set. SMF1 is smoothing filter for
tx-audio signal. The tx-audio signal is then fed to the V102 connector pin 20.
5.1.7 RX-Audio
The rx-audio signal coming from the receiver through the V102 pin 8 is fed to
the audio circuit I405 pin 23. Inside the circuit, the signal is fed to the
operational amplifier (AMP2) inverting input. The amplifier gain is set by
resistors R440 and R441. The signal is next passed through an anti-aliasign
filter. VR5 is a gain control circuit to set the rx-audio signal to the correct level.
Next comes de-emphasis (D/E) circuit. Equalize the pre-empassized rx-audio
signal. The signal passes from the D/E through the switch RXAUDON. RXBPF
is the band-pass filter for the rx-audio signal. RXDET is the rx-audio signal
detection circuit. This circuit works as a full wave rectifier. After the RXBPF
comes expander circuit (EXP). Expand the rx-audio signal amplitude. It can be
bypassed. The linearity is adjustable by the control register EVR. VR6 is a gain
control circuit to set the rx-audio signal to the correct level. After VR6 comes
the RXMUTE switch, which is operated by the RXMUTE control. ADD4 is the
summing junction of the rx-audio signal, external signal (not used), DTMF
signal and transmit signal. VR10 is the volume control circuit to set the level of
earphone and external earphones. The rx-audio signal is connected through
the receiver driver (RECAMP) to the earphone.
5.1.8 FII Signal
The NMT system uses the FII signal to check the radio path quality. This
approx. 4kHz signal is split from the rx-audio signal after the VR5 and is filtered
through the band-pass filter (FBPF). VR7 sets the FII signal to the correct level.
Switch FILOOPON can be operated by the FIION control, to be summed with
the tx-audio signal before the VR4.
5.1.9 FFSK Modem
The FFSK data signal from FFSK modulator to be transmitted is passed
through the FFSK low-pass filter and pre-emphasis (FFSKP-EM) to the VR9,
which adjusts its level. The data signal is switched using switch FFSKTXON.
The data signal is summed with the tx-audio signal by the ADD3.
The received data signal is split from the rx-audio signal after the de-emphasis
circuit. The data signal is fed through the FFSK band-pass filter to the FFSK
demodulator and FFSK data detector.
FFSK DET block. The block works to judge the FFSK signal existence by
comparing the amplitude of the noise reduced FFSK signal and the provided