Agilent Technologies 8564EC, Service Manual

Page: 346 / 512

Chapter 9 451
IF Section
Log Amplifier (P/O A4 Assembly)
CAUTION
Damage to the 8566A/B results if a dc block is not used. The 8566A/B
and many other spectrum analyzers have dc-coupled inputs and cannot
tolerate dc voltages on their inputs.
5. Set the 8566A/B to 4.8 kHz center frequency and 2 kHz span.
6. Connect the VIDEO OUTPUT (rear panel) of the 8564EC or
8565EC spectrum analyzer through a 20 dB attenuator and dc
block to the input of the 8566A/B. Set the sweep time of the 8566A/B
to 10 seconds.
7. Set the 8566A/B to single trigger and press TRACE A
CLEAR-WRITE
.
Trigger a sweep on the 8566A/B and on the signal generator
simultaneously. The 8566A/B should show a 3 dB bandwidth of
600 Hz
±
100 Hz.
8. Reconnect W29 (coax 7) to A5J3.
10.6952 MHz VCXO
Refer to function block E of A4 log amplifier schematic diagram (sheet 2
of 4) in the 8560 E-Series Spectrum Analyzer Component Level
Information.
The purpose of the 10.6952 MHz voltage-controlled crystal oscillator
(VCXO) is to provide an LO for down-converting the peak of the
10.7 MHz IF filter passband to 4.8 kHz. Since the peak of the passband
of the 10.7 MHz IF filters is 10.7 MHz
±
300 Hz, the frequency of the
VCXO is between 10.6949 MHz and 10.6955 MHz. This frequency can
best be measured at the collector of A4Q202.
The center frequency of the 300 Hz resolution-bandwidth filters and the
1 Hz to 100 Hz filters should differ no more than 10 Hz. If the center
frequency is different by more than this, or if no signal is present in the
1 Hz to 100 Hz resolution-bandwidth settings, troubleshoot the
10.6952 MHz VCXO.
Error message
ERR 539
may occur if the VCXO is not oscillating. If
problems exist with the VCXO control voltage, error messages
ERR 536
or
ERR 530
may occur.
Between sweeps the VCXO, at times, is turned off. To prevent the
oscillator from turning off, press
PRESET
,
FREQUENCY
, 0.3
GHz
,
SPAN
,
1
kHz
,
SGL SWP
,
CAL
, and
IF ADJ OFF
.
Input Switch
Refer to function block D of A4 Log Amplifier Schematic Diagram (sheet
2 of 4) in the 8560 E-Series Spectrum Analyzer Component Level
Information.