sunair RT-9000C, Руководство по эксплуатации и обслуживанию

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RT-9000C Hardware Supplement
Document No. 8128000602
Revision A (19 Mar 2007)
8-26
RT-9000 C
When the radio is used in CW Mode, the detected CW signal routed from the 1A2A3 Audio Assembly
enters digital signal processor U401. U401 and direct digital synthesizer U201 generate a shaped CW
output signal directly at 454 kHz.
The 455 kHz Third Local Oscillator is not used in this design to generate IF signals but instead is used to
create a 5.005 MHz clock source. PLL clock generator U202 and 5.005 MHz VCXO U203 are locked to a
frequency 11 times the 455 kHz Third Local Oscillator input signal. Buffered outputs are routed to U201
and IF clock generator U408, which generates and distributes clock signals to the analog, digital, and
data converters.
The output of U201 is sent to low-pass filter consisting of C217, L202, C218, C219, L203, and C220 to
remove undesirable high frequency content. The filtered 455 kHz signal is then switched to the
appropriate 455 kHz filter according to the selected emission mode.
The 455 kHz signal is routed to solid-state switches U3 and U6 whose operation is tied to receive or
transmit-states. In transmit-state, the operation of each switch is dependant upon the selected emission
mode. Signals passing through switch U3 are switched to filter FL2 and used for USB, AME, and CW
transmission.
Signals passing through switch U6 are further switched to filters FL3 or FL4 by solid-state switches U4
and U5. These switches operate together but operate only for specific combinations of emission mode
and Transmit or Receive-states. Filter FL3 is used for LSB and FL4 is used for ISB transmission.
Refer to following table showing how these filter are used when transmitting various emission mode
signals. Note that this filter usage is somewhat different than for receive-state operation.
Transmit-State
Emission Mode vs. Filter Usage
455 kHz Filters
Mode
FL2 FL3 FL4
USB
X
LSB
X
AME X
CW X
ISB X
The signals passing from FL2 and through U4 are combined in transformer T1 and passes to T4. The
signal is then switched through diode gates CR29 and CR24 to mixer X1. The 455 kHz signal is mixed
with the Second Local Oscillator, which has a fixed frequency of 47.850 MHz. This produces the 48.305
MHz transmit IF signal.
The signal is switched by diode gate CR6, amplified by U12, and switched again by diode gate CR3. The
signal next is band-pass filtered and switched by diode gate CR2 to amplifier U13. The amplified signal is
passed to an attenuator consisting diodes CR9 and CR10. This attenuator can be controlled by ALC or
TGC feedback signals that control transmitter power output based on RF load conditions or emission
mode. The signal from the attenuator is amplified by U14 and finally routed to the 1A2A5 Front End
Assembly through coaxial connector P3.
Automatic Level Control (ALC) sets transmit power level based on forward and reflected power signals
routed from the 1A3 Filter Assembly. U9, U19, and U20 produce a control voltage sent to attenuator
diodes CR9 and CR10.
Transmitter Gain Control (TGC) is a special ISB Mode-related feedback signal. This signal is based on
the power of the USB and LSB audio input and the power indicated by the TGC Power Detect signal. This
signal is developed by digital signal processor U401 and allows it to set a lower output power than the
ALC circuit would set. The ALC function remains active but is not the dominant control.