If Filter - Module; Fig. 3-4 If Filter - Rohde & Schwarz FSP3 Service Manual

R&S FSP
IF Filter – Module
The frontend in the signal path is followed by the IF filter module (analog IF):
X132
Selfttest detector
A
RBW 100kHz
XTAL-Filter
X131
CAL_Amp1 CAL_Amp2
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.
1164.4556.82
Instrument Design and Function Description
IF-FILTER BOARD
Signal Path and selftest
selfttest detector
B
RBW 300k ... 3M
LC-Filter I
RBW 10MHz
StepGain
-10...+40 dB
/ 10 dB
Selftest detektor
C
RBW 300k ... 3M
LC-Filter II
RBW 10MHz
StepGain
0...+10 dB
/ 0.1 dB
3.5
X146
dither source
Selftest detektor
RBW 100kHz
calib.
only
LIN
Detecktor
LOG
RBW 300kHz
D
X147
E-1