HP 8566B Adjustment Manual page 315

input mixer. In Band F (the external mixing bands), the output of an
external harmonic mixer is connected to the front-panel 321.4 MHz IF
INPUT, bypassing the two internal mixers.
The frequency response of the spectrum analyzer is mainly
determined by the two input mixers - the A6A6 First Converter
Assembly and A6A8 YTX Assembly - and the associated A6A5
Amplifier/Coupler/Load Unit (ACLU) Assembly. Additional signal
path components that affect frequency response include the A6J3
RF INPUT Connector Assembly, A6Al Coaxial RF Switch, A6A2 RF
Attenuator, A6A14 Limiter, and semi-rigid cables A6W1, A6W2,
adjusted or replaced, the spectrum analyzer frequency response must
be verified and adjusted as necessary.
To adjust frequency response, an externally-leveled synthesized
sweeper is used as a reference signal source. The synthesized sweeper
output is connected to the spectrum analyzer RF INPUT using a
low-loss microwave cable, a precision resistive splitter, and a power
sensor or planar-doped, barrier diode detector. The power meter or
detector output is connected to the synthesized sweeper LEVELING
EXT INPUT to precisely level the signal power at the input of the
spectrum analyzer. Since the synthesized sweeper and spectrum
analyzer both sweep independently of each other, one must be swept
quickly relative to the other to review the frequency response across
a given frequency band.
The f9 Vdc precision reference is initially checked and adjusted.
Then, the drive current to the A6A4 Second Converter 3.3 GHz
oscillator is set at 15 mA, and the SWEEP+TUNE offset is adjusted
for Band A.
Over each frequency band, the leveled reference signal from the
synthesized sweeper is used to adjust the spectrum analyzer for
optimum flatness and amplitude. In Band A (100 Hz - 2.5 GHz, not
preselected), overall RF gain and flatness are adjusted. In Bands B,
C, D, and E (2 GHz - 22 GHz), the adjustments necessary to align
the A6A8 YIG-Tuned Mixer (YTX) include YTX mixer diode biasing,
the A6A8 YTX is aligned in each of these four preselected bands,
RF Gain and flatness are then optimized with the Preselector DAC
centered at the default setting of 32 and the YTX modulated with a
20 Hz sinusoid. In the external mixing bands (Band F), the conversion
loss is set to 30 dB and the spectrum analyzer RF gain is adjusted with
a 321.4 MHz, -30 dBm reference signal connected to the front panel
32 1.4 MHz IF INPUT.
Synthesized Sweeper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HP 8340A/B
Power Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..HP436 A
Power Sensor (50 MHz to 18 GHz) . . . . . . . . . . . . . . . . . . . . . . . . . HP 8481A
Frequency Synthesizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HP 3335A
Digital Voltmeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HP 3456A
Pulse/Function Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HP 8116A
Planar-doped Barrier Diode Detector (10 MHz to 33 GHz) ........ HP
Power Splitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HP 11667B
2 1. Frequency Response Adjustments
Adjustments 3-175