Rohde & Schwarz M3SR Series 4100, Service Manual, Page: 50 / 138

R&S M3SR Series 4100 HF Transceivers Frontend - Function
6124.9007.82.01 1.14
In TX mode a D/A converter generates the modulated 48 kHz IF signal for transmit mode. This signal
is filtered and afterwards transformed for the image rejection mixer. The second mixer and crystal filter
are used in TX mode to mix the 2nd IF (48 kHz) to the 1st IF (40.048 MHz). The AGC amplifier is de-
activated in TX mode. The first mixer is used to mix 1st IF of 40.048 MHz to the TX frequency. The
preamplifier generates the exciter output signal.
+10 dBm TX output level control
In order to have a constant TX output level (+10 dBm) for all frequencies, a fitting process is done, re-
sulting in a look-up table stored in the FLASH. For each TX frequency, the correspondent table value
is read. Via a D/A converter the table value is converted to a DC value ALC (Automatic Level Control),
to control the TX D/A converter output level.
Fig. 1.5 Frontend, Block Diagram
ICN-S4100-A-E11100-R-D0894-00203-A-01-1
Tx/Rx
Rx
Overvoltage
Detection
RCB
10 dB
30 MHz
digital Tx/Rx
Signal
I/O
Inhibit
FPGA
A/D
Flash
90°
0°
80 MHz
LO 2=
2nd IF
48 kHz
2nd Mixer
AGC
40.058 - 70.048 MHz
LO 1
Filter
1st Mixer
1st IF
40.048 MHz
Tx
X1
X2
D/A
AGC regulator
A/D
AGC
D/A
Vref
Tx
A/D
PLL
IF
Clock
12.288 MHz
D/A
AF-
Test
Output
100 kHz
Ref. Freq.
DIV
2
ESSI