Tektronix RSA3408, Руководство по обслуживанию

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Theory of Operation
2- 2
RSA3408B Analyzer Service Manual
In the baseband, an input signal enters the 1
st
Converter. Then the signal path is
switched with a relay and the signal is sent directly to the A10 A/D board for
A/D conversion. In the RF1 band, an input signal goes through all converters
(1
st
, 2
nd
, and 3
rd
). In the RF2 and RF3 bands, an input signal is directly
frequency-converted by the 1
st
Converter into the 2
nd
IF signal of approximately
421 MHz, then sent directly to the 3
rd
Converter, bypassing the 2
nd
Converter.
The RF2 module consists of the 2
nd
Converter, 2
nd
IF Filter, and 2
nd
Local
Oscillator (LO). The 1
st
IF signal sent from the 1
st
Converter passes through a
Bandpass Filter and a Lowpass Filter for removal of unnecessary frequency
bands. After this, the 1
st
IF signal enters the 2
nd
Converter. In the 2
nd
Converter,
the 1
st
IF signal is mixed with the 2
nd
LO signal and frequency-converted into
the 2
nd
IF signal of approximately 421 MHz.
The same is true of 1
st
LO; the 2
nd
LO frequency is controlled by a synthesizer
circuit (RF4 module) to stabilize the LO output frequency. The 2
nd
IF signal is
sent to the 2
nd
IF Filter, which has two filters with the pass bandwidth of
40 MHz and 4 MHz, respectively.
The RF5 module consists of the 3
rd
Converter and the 3
rd
IF Gain block. In the
3
rd
converter, the signal is mixed with the 3
rd
LO signal and then frequency-con-
verted into the 3
rd
IF signal of 76 MHz normally, which is changed to 39 MHz in
an ACLR measurement with the sweep mode. In the RF2 and RF3 bands, the 2
nd
IF signal from the RF2 module enters the band switching relay in the input
section of the 3
rd
Converter.
The 3
rd
IF Gain block consists of a Step Amplifier of 12 dB/step with the
maximum gain of 60 dB and a Step Attenuator with the maximum attenuation of
31 dB. This block maintains the 3
rd
IF signal to be sent to A/D Converter at an
appropriate level, and adjusts the accuracy of conversion gain.
The RF6 module consists of the 3
rd
IF Filter block, Oscillator block, and
10 MHz Reference Oscillator. The 3
rd
IF signal enters the 3
rd
IF Filter containing
two filters with the pass bandwidth of 40 MHz for 76 MHz IF and 1.2 MHz for
38 MHz IF, respectively, which are software-selectable.
The Oscillator block contains the 3
rd
local oscillator with the local frequency of
345 MHz for 76 MHz IF or 383 MHz for 38 MHz IF, and A/D clock with the
clock frequency of 102.4 MHz. Both the 3
rd
LO signal and A/D clock signal
generated in the Oscillator block are highly stabilized signals locked with a
10 MHz reference signal, and are output to the 3
rd
Converter and A10 A/D
board, respectively.
RF2 Module
RF5 Module
RF6 Module