R&S FSP Instrument Design and Function Description
1164.4556.82 3.5 E-1
IF Filter – Module
The frontend in the signal path is followed by the IF filter module (analog IF):
calib.
only
XTAL-Filter
LOG
dither s ource
LIN
Detecktor
X147
X146
X131
X132
CAL_Amp1 CAL_Amp2
-10...+40 dB
/ 10 dB
StepGain
0...+10 dB
/ 0.1 dB
RBW 300k ... 3M
RBW 10MHz
RBW
100kHz
RBW 10MHz
RBW 300k ... 3M
IF-FILTER BOARD
Signal Path and selftest
RBW
100kHz
RBW
300kHz
ABC D
LC-Filter IILC-Filter I
Selfttest detector selfttest detector Selftest detektor Selftest detektor
Fig. 3-4 IF filter
The R&S FSP offers resolution bandwidths from 1 Hz to 10 MHz in steps of 1/3/10. The selection filter at
the second IF of 404.4 MHz in the frontend yields the 10 MHz bandwidth. Selection is not performed at
the IF of 20.4 MHz.
The tunable bandwidths from 300 kHz to 3 MHz are at the third IF (20.4 MHz) on the IF filter module.
The bandwidths from 100 kHz to 3 MHz are provided by 4 decoupled LC circuits.
The IF filter module also comprises circuits for the IF gain (step gain) from 0 to 50 dB in 0.1 dB steps,
level correction for all bandwidths and frequency response correction using a variable gain amplifier
each.
The IF filters are followed by a log detector to obtain the display dynamic range.
The module also comprises a limiting amplifier (in the log-amp) with a TTL output for the frequency
counter.
For the digitally implemented resolution bandwidths from 1 Hz to 120 kHz, the 20.4 MHz IF signal at the
IF filter output is routed to the A/D converter.
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