R&S SMU200A Instrument Design and Function Description
1007.9845.82 3.5 E-6
LF AM
Two modulation inputs of narrow bandwidth are available as the LF AM source. They can be selected
via a switching matrix. Either DC or AC coupling is possible. The modulation depth can be set from 0 to
100% using a DAC. The signal is fed into the Q channel of the baseband processing module.
Pulse Matrix/Blank/RF_DOWN_N
The pulse matrix can be used to switch either one of the two modulation inputs of narrow bandwidth or
the pulse line to the pulse modulator output for the IQOP3 RFM and IQOP6. The switching logic can be
inverted. The RF_DOWN_N line (from the attenuator) and the BLANK line (from the DAC IF board) are
hard-wired to the two pulse outputs.
Levatt
The two Levatt signals are filtered out and forwarded to the DSP controller and the RFM.
Radio Frequency Module RFM
The RFM contains the following elements:
• I/Q modulator with bypass for CW signals for reducing the broadband noise in the CW operating
modes
• 15/30/45 dB LEVATT attenuation (for slot attenuation with digital modulation)
• 15 dB LEVELPRESET attenuation, adjustable in 1 dB steps
• 6 switchable lowpass filters for suppressing harmonics after the first preamplifier
• Pulse modulator with typ. 100 dB reduction
• Switchable amplifier for high output power (for overrange operating states)
• LEVEL CONTROL: PIN diodes for level reduction with typ. 30/60 dB in the normal range/overrange
• Mixing range with 1040 MHz or 1200 MHz local oscillator
• Switchable 5 dB attenuator for generating 5 dB steps in the output power
• Output amplifier with 3 switchable harmonic filters
• Directional coupler + detector attenuator + rms level detector with thermostat
Switching Sequence
Operating the MIX_A mixer switch is allowed only when PULSE_SWITCH=ON.
This precaution prevents "hot switching", which can destroy the mixer switch.
Interrupts
IRQ_UTHERMOX
The RFM thermostat requires a settling time of two minutes (maximum) to reach the nominal
temperature. The interrupt IRQ_UTHERMOX line is H (+3.3 V) if the thermostat temperature deviates
more than +-1 °C from the nominal temperature (70 °C). This generates a correspondent error
mesage.
IRQ_QUADX
If the I/Q modulator quadrature control loop is out of range, this interrupt will be triggered and a error
message is generated.
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