Simoco EMEA Ltd SDB670AC01 Manual De Usuario
SDB670 – SERVICE MANUAL
TNM-M-E-0032
May 13
Page 38
TECHNICAL DESCRIPTION
U702 operates at 21.6 MHz and is specified at ±0.5 ppm frequency stability over the temperature
range –30 °C to +85 °C. Its output drives Clock Synthesiser U720 to provide two digital 21.6 MHz
outputs and a 95.04 MHz output. The 95.04 MHz output is used as the reference frequency for the
PLL as described above. The 21.6 MHz output SYN-ACLK is used as the clock for the Rx ADC
U401 and the other 21.6 MHz output SYN-DCLK1 goes via Schmitt Trigger U307 to provide SYN-
FCLK1 to clock the FPGA and also the DSP.
range –30 °C to +85 °C. Its output drives Clock Synthesiser U720 to provide two digital 21.6 MHz
outputs and a 95.04 MHz output. The 95.04 MHz output is used as the reference frequency for the
PLL as described above. The 21.6 MHz output SYN-ACLK is used as the clock for the Rx ADC
U401 and the other 21.6 MHz output SYN-DCLK1 goes via Schmitt Trigger U307 to provide SYN-
FCLK1 to clock the FPGA and also the DSP.
5.3.4.5
VCO’s
The Tx and Rx VCO’s use low noise transistors Q602 (Rx), Q604 (Tx) and associated parts to
generate the signals for the required band coverage. Electronic tuning is provided by varactor
diodes D604 to D615 where fitted with their control voltage CPP-RF derived from the Loop Filter
and PLL. A Negative Bias Generator is used to apply an adjustable negative bias to the varactor
anodes to extend their tuning range. VCO switching and timing is controlled by the DSP/FPGA via
the 5V-RX and 5V-TX power supplies and applied through switches Q607 (Rx) and Q608 (Tx).
VCO buffer Q605/Q606 isolates the VCO from load variations in following circuits and active power
supply filter Q600 minimises supply related noise. A PLL feedback signal is sampled from the
VCO buffer output via buffer Q710. The output from the VCO Buffers is passed through Tx/Rx
switch D700/D701, which switches it between either to the Mixer input or Tx Buffer. This switch is
controlled by the 5V-RX supply.
generate the signals for the required band coverage. Electronic tuning is provided by varactor
diodes D604 to D615 where fitted with their control voltage CPP-RF derived from the Loop Filter
and PLL. A Negative Bias Generator is used to apply an adjustable negative bias to the varactor
anodes to extend their tuning range. VCO switching and timing is controlled by the DSP/FPGA via
the 5V-RX and 5V-TX power supplies and applied through switches Q607 (Rx) and Q608 (Tx).
VCO buffer Q605/Q606 isolates the VCO from load variations in following circuits and active power
supply filter Q600 minimises supply related noise. A PLL feedback signal is sampled from the
VCO buffer output via buffer Q710. The output from the VCO Buffers is passed through Tx/Rx
switch D700/D701, which switches it between either to the Mixer input or Tx Buffer. This switch is
controlled by the 5V-RX supply.
In addition, each VCO includes an RF negative feedback network (ALC) to set their operation
levels for optimum noise reduction. This is achieved via diodes D616 to D619 that rectify the RF
signal. This is filtered and applied to input pins on op-amp U600, which provides amplified
correction voltages to the base bias of Q602 and Q604. This circuit also contains a means of
presetting and monitoring of the operating current via VCO-BIAS and SYN-ALCSET. The SYN-
ALCSET value is factory preset and stored in Flash.
levels for optimum noise reduction. This is achieved via diodes D616 to D619 that rectify the RF
signal. This is filtered and applied to input pins on op-amp U600, which provides amplified
correction voltages to the base bias of Q602 and Q604. This circuit also contains a means of
presetting and monitoring of the operating current via VCO-BIAS and SYN-ALCSET. The SYN-
ALCSET value is factory preset and stored in Flash.
5.3.5
Audio Processing
Refer to Figure 10 (page 42) and Figure 5 in TNM-S-E-0005, SDM600 Series – Issue 4 Circuit
Diagrams [2].
Diagrams [2].
5.3.5.1
Receiver Audio
The baseband quadrature signal sent to the DSP U203 is converted into a single digital data input
CD-DIN to the Coder-Decoder (CODEC) U803, which in turn converts it into an analogue signal
after further processing.
CD-DIN to the Coder-Decoder (CODEC) U803, which in turn converts it into an analogue signal
after further processing.
All Rx audio processing and filtering functions are performed by the CODEC under the control of
the DSP. These include de-emphasis, mute noise processing, mute control and volume control for
narrow and wideband operation. A CODEC DAC then converts the fully processed signal to an
analogue audio signal. Independent processing can be achieved on four separate outputs C-
OUT1, C-OUT2, C-OUT3 and C-OUT4, which enables great flexibility to suit customer
requirements. C-OUT3 normally provides volume controlled, de-emphasised audio to the audio
PA U808 via differential amplifier U804A. With a normal radio FPP configuration, the maximum
sinusoidal output is limited to 4 V
the DSP. These include de-emphasis, mute noise processing, mute control and volume control for
narrow and wideband operation. A CODEC DAC then converts the fully processed signal to an
analogue audio signal. Independent processing can be achieved on four separate outputs C-
OUT1, C-OUT2, C-OUT3 and C-OUT4, which enables great flexibility to suit customer
requirements. C-OUT3 normally provides volume controlled, de-emphasised audio to the audio
PA U808 via differential amplifier U804A. With a normal radio FPP configuration, the maximum
sinusoidal output is limited to 4 V
RMS
across the 4 Ω speaker. However, when more power is
required, it is possible to achieve up to 16 W into a suitable 4 Ω speaker.
In addition to the CODEC mute control, the audio PA is also muted on and off via inverter Q800
and CD-SPKRON derived from the FPGA. The other CODEC outputs C-OUT2, C-OUT3 and C-
OUT4 can provide any combination of audio characteristics including muted, unmuted, de-
emphasised, flat and volume dependency.
and CD-SPKRON derived from the FPGA. The other CODEC outputs C-OUT2, C-OUT3 and C-
OUT4 can provide any combination of audio characteristics including muted, unmuted, de-
emphasised, flat and volume dependency.
All CODEC outputs are fed to analogue gate U806 via differential amplifiers U804 and U805. This
enables switching flexibility to the radio connectors S1-4 (LINE-OUT1), S3-1 (LINE-OUT3) and S5-
18 (LINE-OUT2).
enables switching flexibility to the radio connectors S1-4 (LINE-OUT1), S3-1 (LINE-OUT3) and S5-
18 (LINE-OUT2).