HP 8360 Working with Spectrum Analyzers/Reverse Power Effects, 1-32Getting Started Advanced

Working with Spectrum Analyzers/Reverse Power Effects

Reverse power is a problem with spectrum analyzers that do not have preselection capability. Some analyzers have as much as

+5 dBm LO feedthrough coming out of their RF input, at some frequencies. The effects of reverse power are less in the heterodyne band (0.01 to 2.3 GHz) where the power amplifier provides some broadband matching. Similarly, at frequencies above 2.3 GHz, reverse power that is within 10 MHz of the synthesizer’s frequency may be partially absorbed by the YIG filter. If the frequency difference is small enough to be within the leveling system bandwidth (typically 10 kHz CW, 200 kHz sweep or AM), the effect of reverse power is amplitude modulation of the synthesizer’s output. The AM rate equals the difference in RF frequencies. Reverse power problems may be treated by using the unleveled mode. There are two unleveled modes, ALC off and search.

To set the synthesizer to the ALC off mode:

1.Refer to menu map 1.

2.Press (ALC).

3.Select Leveling Mode ALCoff .

In this mode, the synthesizer provides RF power with no ALC correction and therefore requires a power meter to set a particular power.

To set the synthesizer to the search mode:

1.Press (ALC.

2.Select Leveling Mode Search.

In this mode, the synthesizer is in the normal ALC mode until the desired power level is reached, then the ALC is disconnected.

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