Positive/Negative Peak Detectors
Refer to function blocks Y and Z of A3 Interface Assembly Schematic Diagram in the
HP 8560 E-Series Spectrum Analyzer Component Level Information.
The following information pertains to the positive peak detector and is applicable to
troubleshooting the negative peak detector.
The positive peak detector consists of an input amplifier (A3U204 and A3Q210) followed
by detector diodes (A3CR203 and A3CR204) and hold capacitor A3C217. Output amplifier
A3Q206, Q211, and Q212 buffers the hold capacitor. Both the input and output amplifiers
have a gain of one. Each amplifier has local feedback. On the output amplifier the emitter
of
Q212
connects to the gate of
Q206.
On the input amplifier the feedback goes through
Q209 and Q208 back to the base of U204D. Global feedback occurs from the output amplifier
through R223 back to the input amplifier U204D. The peak detector resets through Q207.
1.
Press (PRESET) and set the spectrum analyzer controls as follows:
2.
Centerfrequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz
Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..500MHz
Resolution bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AUTO
Videobandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..AUTO
Log dB/division . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 dB/DIV
If the spectrum analyzer does not meet the conditions in steps a through e below, the
positive and negative peak detectors are probably faulty. Continue with step 3 to check
the detectors.
a.
b.
C.
d.
The peak-to-peak deviation of the noise in NORMAL detector mode should be
approximately two divisions. Press
(TRACE),
TMCE
B ,
CLEAR
WRITE
3 ,
YIEU
B ,
TRACE
1,
MORF.
1
of 3 , and DETECTOR MODES .
Select

DESECTDR

POS PEAK

mode.
e.
Confirm that the noise is about one-third division peak-to-peak. The noise should also
be no higher than the top of the noise level in NORMAL detector mode.
Select

DETEXTOR

NEG

PEAK mode. The noise should be about one-third of a division
peak-to-peak. The noise should also be no lower than the bottom of the noise in
NORMAL mode.
Select
DETECTOZt
SAMPLE mode. Check that the noise appears between the top and
bottom of the noise in NORMAL mode.
3.
4.
5.
6.
On the spectrum analyzer, connect the front-panel CAL OUTPUT to the INPUT
500
and set the controls to the following settings:
Center frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz
Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz
Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 s
Detector mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . POS PEAK
Monitor
A3TP17
and
A3TP16
simultaneously with an oscilloscope.
Change the reference level from -10
dBm
to
+30
dBm
and verify a voltage change at
both
A3TP17
and
A3TP16
of 0.9 V to 0.5 V in 100
mV
steps.
Check the entire range of the detector by substituting a dc source at
JlOl
and varying its
output from 0 V to 1 V.
ADC/lnterface
Section 8-19