Operating Instructions

Measurement Graticule

The 1705A is equipped with an internal graticule crt. The graticule has an 8 X 10 division scale that is lighted. Scale brilliance is controlled by the front-panel SCALE control. Figure 2-4 shows the 1705A graticule. Refer to this figure and subsequent figures when reading the following discussion of the graticule.

Tek

+ f

REF

-10

-20

-30

-40

-50

-60

-70

L

O

G

Figure 2-4: 1705A graticule scale

Vertical Scales The vertical scale is eight divisions in height. The center vertical scale is broken into five equal minor divisions per major division. Note that the 0 dB reference is at the top of the graticule and that 80 dB (maximum division) is at the bottom of the graticule. There are two gain selections: normal gain (10 dB/div) and high gain (2 dB/div). In normal gain mode, major divisions are 10 dB, which makes each minor division 2 dB. When the GAIN front-panel push button is held, high gain is selected, and major divisions are approximately 2 dB, which makes minor divisions about 0.4 dB each.

Since dB is a dimensionless ratio, and there are several scale variations, it is essential that there be some discussion of the various scales. The unit of measure described as dB (decibel) is 10 LOG P1/P2. If there is a specific scale defined (m, k, w, p, etc.), there is a specific reference point established. The 1705A has input specifications in dBm, which means that they are referenced to 1 mW (milliwatt). Therefore, -30 dBm is 30 dB below 1 mW. Table 2-1 is a handy reference table for dB and dBm. Table 2-2 provides a reference for conversion from dBm to ￿v.

1705A Spectrum Monitor

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Tektronix instruction manual Measurement Graticule, 1705A graticule scale