Reducing Input Attenuation On Spectrum Analyzer

The ability to measure a low-level signal is limited by internally generated noise in the spectrum analyzer. The measurement setup can be changed in several ways to improve the analyzer sensitivity. The input attenuator affects the level of a signal passing through the instrument. If a signal is very close to the noise floor, reducing input attenuation can bring the signal out of the noise.Spectrum Analyzer

Ensure that the total power of all input signals at the analyzer RF input does not exceed +30 dBm (1 watt).

Step 1.Preset the analyzer:

Step 2. Set the frequency of the signal source

  • Press FREQUENCY 300 MHz
  • Press Amplitude −80 dBm.
  • Connect the source RF OUTPUT to the spectrum analyzer RF INPUT.

Step 3.Set the center frequency, span and reference level:

Step 4.Move the desired peak (in this example, 300 MHz) to the center of the display:

Step 5.Reduce the span to 1 MHz (as shown in Figure) and if necessary re-center the peak:

  • Press Span  1 MHz.Reducing Input Attenuation

Step 6.Set the attenuation to 20 dB:

Note that increasing the attenuation moves the noise floor closer to the signal level.

A “#”mark appears next to the Atten annotation at the top of the display, indicating that the attenuation is no longer coupled to other analyzer settings.

Step 7.To see the signal more clearly, set the attenuation to 0 dB:

See Figure shows 0 dB input attenuation.

Reducing Input Attenuation

Warning When you finish this example, increase the attenuation to protect the analyzer’s RF input: