622 Chapter12
RF Section
A15 RF Assembly
3. Press SGL SWP, CAL, IF ADJ OFF.
4. Disconnect W29 (coax 7) from A15J601.
5. Connect a test cable from A15J601 to the input of another spectrum
analyzer.
6. Tune the other spectrum analyzer to 10.7 MHz. The signal displayed
on the other spectrum analyzer should be approximately −15 dBm.
7. Remove the test cable from A15J601 and reconnect W29 to A15J601.
Third Converter
Refer to function blocks A, B, C, D, and E on A15 RF Section Schematic
Diagram in the 8560 E-Series Spectrum Analyzer Component Level
Information.
The 3rd converter consists of the 2nd IF distribution, 2nd IF amplifier,
double balanced mixer, 10.7 MHz bandpass filter, and flatness
compensation amplifier. The 2nd IF distribution switches between two
possible 2nd IF inputs: the internally generated 2nd IF, or the external
mixing IF INPUT. A variable dc bias can be applied to the IF INPUT for
external mixers which require such bias. The selected input is fed to the
2nd IF Amplifier. This amplifier consists of four stages of gain and two
stages of SAW filters for image frequency rejection.
The flatness compensation amplifier consists of two fixed-gain stages
and two stages of variable gain. This provides an overall adjustable
gain of 4 dB to 30 dB. This gain is adjusted during a spectrum analyzer
sweep to compensate for front end conversion loss versus frequency.
The gain of the flatness compensation amplifiers is driven to a
minimum by the REDIR line going low during automatic IF
adjustment.
The 10.7 MHz bandpass filter provides a broadband termination to the
mixer while filtering out unwanted mixer products. Perform the
following steps to test the amplifier gain:
1. On the spectrum analyzer, press
AUX CTRL, then INTERNAL MIXER.
2. In the 2nd IF distribution (function block A), diode CR802 should be
forward biased and diode CR801 should be reverse biased.
3. Disconnect W35 (coax 92) and connect a signal source to A15J801.
Set the source to the following settings:
Frequency ............................................................. 310.7MHz
Amplitude ................................................................ −30dBm
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