Chapter 11 599
RF Section
A15 RF Assembly
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
in the
HP 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 (non-Option 002 spectrum analyzers only). 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 an spectrum
analyzer sweep to compensate for front-end conversion loss versus
frequency. Perform the following steps to test the amplifier gain:
The 10.7 MHz bandpass filter provides a broadband termination to the
mixer while filtering out unwanted mixer products.
1. On the HP 8560E/EC, 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
4. Use an active probe with another spectrum analyzer to measure the
signal at A15TP601 (function block C). The signal should measure
−17 dBm ±4 dB confirming the operation of the 2nd IF Amplifier.
5. Use an active probe with another spectrum analyzer to measure the
300 MHz into the LO port of the third mixer. The signal should
measure at least +20 dBm.
6. Measure the power of the mixer 10.7 MHz IF output. The signal
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