HP 8562E, Service Manual

Page: 443 / 482

Refer to function blocks A, B, C, D, and E on Al5 RF Section Schematic Diagram (sheet 4 of
4)
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
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 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
to 30 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 filter provides a broadband termination to the mixer while filtering
out unwanted mixer products.
1. On the HP 85623, press then .
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 Set the source to the
following settings:
Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Amplitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -30
For troubleshooting, it is recommended that you use an active probe, such
as an HP
and another spectrum analyzer. If an HP 1120A active
probe is being used with a spectrum analyzer having dc coupled inputs, such
as the HP HP
and the HP either set the active
probe for an ac-coupled output, or use a dc-blocking capacitor between the
active probe and the spectrum analyzer input. Failure to do this can result in
damage to the spectrum analyzer or the probe.
4. Use an active probe with another spectrum analyzer to measure the signal at
(function block C). The signal should measure -17 confirming the operation
of the 2nd IF Amplifier.
5. Use an active probe with another spectrum analyzer to measure the 300 MHz signal into
the LO port of the third mixer. The signal should measure at least
6. Measure the power of the mixer 10.7 MHz IF output. The signal level should be
approximately -22
7. Move the WR PROT/WR jumper on the A2 controller assembly to the WR
position.
8. While measuring the 10.7 MHz IF output signal at the mixer, adjust the signal source
until the level of the 10.7 MHz IF is -40
RF Section 12-17