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2 1. Frequency Response Adjustments

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

Attenuator,

A6A14

Limiter, and semi-rigid cables

A6W1,

A6W2,

A6W3,

A6W4,

A6W5,

and

A6W20.

When any of these components is

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

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

GHz),

the adjustments necessary to align

the

A6A8

YIG-Tuned Mixer (YTX) include YTX mixer diode biasing,

YTX/YTO

tracking and linearity, and YTX delay compensation. After

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

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.

Equipment

Synthesized Sweeper

.....................................

8340A/B

Power Meter

...............................................

..HP436

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)

........

8473D/8474C

Power Splitter

.............................................

HP 11667B

Adjustments 3-175

1 2 ... 310 311 312 313 314 315 316 317 318 319 320 ... 404 405

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