Agilent Technologies 22A Specifiche Scaricare il pdf (Pagina 90)

The word eliminate may be a little strong. Preselectors do not have infinite

rejection. Something in the 70 to 80 dB range is more likely. So if we are

looking for very low-level signals in the presence of very high-level signals,

we might see low-level images or multiples of the high-level signals. What

about the low band? Most tracking preselectors use YIG technology, and

YIG filters do not operate well at low frequencies. Fortunately, there is a

simple solution. Figure 7-3 shows that no other mixing mode overlaps the

–

mixing mode in the low frequency, high IF case. So a simple low-pass filter

attenuates both image and multiple responses. Figure 7-8 shows the input

architecture of a typical microwave spectrum analyzer.

5.3

4.7

4 4.4

5 5.6

–

LO frequency (GHz)

Preselector

bandwidth

Signal frequency (GHz)

Figure 7-7. Preselection; dashed lines represent bandwidth

of tracking preselector

3 GHz

3 - 7 GHz

Sweep generator

Display

3.9214 GHz

Analog or

Digital IF

321.4 MHz 21.4 MHz

3.6 GHz

external

mixer

321.4 MHz

Preselector

300 MHz

Input

signal

Atten

Low band

path

High

band path

Figure 7-8. Front-end architecture of a typical preselected spectrum analyzer

1 2 ... 85 86 87 88 89 90 91 92 93 94 95 ... 119 120

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Agilent Technologies 22A Specifiche Pagina 90

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