R&S PR100 User Manual
5 Operating principle
Frontend
Starting from the antenna socket, the frequency in the signal path is limited to 8 GHz.
Signal processing then takes place in three paths for three different frequency
ranges. Signals from 9 kHz to 30 MHz are routed via a preamplifier directly to the A/D
converter. Signals from 20 MHz to 3.5 GHz are taken to the IF section via a
preselection and a preamplifier, or via an attenuator in the case of high signal levels.
The preselection as well as the attenuator effectively protect the IF section against
overloading. This is particularly important in this frequency range, where the
maximum signal sum levels occur. Signals from 3.5 GHz to 8 GHz are taken to the IF
section via a preamplifier. The three-stage IF section processes the signals from 20
MHz to 8 GHz for the subsequent A/D converter. To provide optimum instrument
performance, only signals up to 7.5 GHz are processed in the subsequent stages.
The uncontrolled 21.4 MHz IF can also be tapped ahead of the A/D converter via a
BNC socket of the R&S®PR100 for further external processing.
Digital signal processing
After A/D conversion of the signal, the signal path is split up: In the first path, the IF
spectrum is calculated by means of a digital downconverter (DDC), a digital
bandpass filter and an FFT stage. The bandwidth of the bandpass filter can be
selected between 10 kHz and 10 MHz. Before the IF spectrum is output on the
display or via the LAN interface, results are postprocessed by means of the
AVERAGE, MIN HOLD or MAX HOLD function as selected by the user. In the
second path, the signal is processed for level measurement or demodulation. Here,
too, the signal is taken via a DDC and a bandpass filter. To process the different
signals with optimum signal-to-noise ratio, the receiver contains IF filters with
demodulation bandwidths from 150 Hz to 500 kHz, which can be selected
independently of the IF bandwidth. Prior to the level measurement, the absolute
value of the level is determined and weighted by means of the AVERAGE, MAX
PEAK, RMS or SAMPLE function, as selected by the user. The measured level is
then output on the display or via the LAN interface. For the demodulation of analog
signals, the complex baseband data is subjected to automatic gain control (AGC) or
manual gain control (MGC) after the bandpass filter. It is then applied to the AM, FM,
USB, LSB, ISB, PULSE or CW demodulation stage. The complex baseband data (I/Q
data) of digital signals is directly output for further processing after the AGC/MGC
stage.
The results obtained are available as digital data and can be output via the LAN
interface as required for the particular task. Digital audio data are reconverted to
analog signals for output via the loudspeaker.
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