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Spectral math magnitude controls

Vertical units can be either linear or log. You can select from the following choices by clicking the Math menu button. Then select

the Spectral Analysis Setup command.

Mag tab

Select the desired scale type, Linear, dB, or dBm:

■

Linear. When the spectrum is linear magnitude the vertical units are the same as the source waveform. Usually this is volts.

However, it may also be watts or amperes.

■

dB. This sets the vertical scale of the magnitude spectrum to dB. Use the Reference Level Offset to set which vertical

position in the magnitude spectrum will be zero dB. The following equation applies:

dB = 20 log (|X| - Ref)

Where X is a complex data point in the spectrum and Ref is the Reference Level Offset value.

■

dBm. This selects dB as described in the above equation, but also sets the Reference Level Offset to a value that is

equivalent to 1 mW of power into 50 ohms. Therefore, if the input units are volts, then the value is set to 223.6 mV. If the

input units are amperes, then the value is set to 40 mA. If the input units are watts, then the value is set to 1 mW.

Reference level

This sets the vertical position of the displayed spectrum. Its

value is the magnitude at the top of the display screen. When

this control is adjusted, the spectral waveform along with its

zero reference marker move vertically on the screen as shown.

This control does not change the spectral data.

Oscilloscope reference

722 DPO70000SX, MSO/DPO70000DX, MSO/DPO70000C, DPO7000C, and MSO/DPO5000B Series

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