Introduction to the Spectrum Analyzer Lab

1
Introduction to the Spectrum Analyzer Lab

• Donna Kubik
• 15 Sept 2009

2
Spectrum analyzers

• Spectrum analyzers are cleaverly designed
  instruments that detect the frequency content of
  an input signal
• In this lab, an Agilent MXA Signal Analyzer
  (20Hz-2.6GHz) was used.
• A signal analyzer can be thought of as a
  souped-up spectrum analyzer

3
Initial setup
4
Initial setup (Steps 1-5)

• Starting with 10 MHz input signal and setting 10
  MHz as center frequency
• RBW910 kHz
• VBW910 kHz
• SWP1.00 ms
• Peak search yields
• Signal -16.57 dBm

5
Initial setup (Steps 6-7)

• Change span to 50 kHz
• RBW 470 Hz
• VBW 470 Hz
• SWP 273 ms
• Peak search yields
• Signal -16.57 dBm (changed)
• Accd to lab, this should not have changed?
• Learned that RBW, VBW, and SWP are coupled
  functions with span

6
Initial setup (Step 8-9)

• Decrease sweep to 100 ms
• Now its uncalibrated!!!
• RBW 470 Hz
• VBW 470 Hz
• SWP 100 ms
• Peak search yields
• Signal -58 dBm, but it is not stable

7
Initial setup (Step 10)

• Decrease RBW manually
• RBW and VBW still change together? I thought
  only RBW would change if Im using manual
  control?
• The 100 MHz peak is now resolved.

8
Signal measurements
9
Signal measurements (Steps 12-15 )

• Input 1 MHz signal from the function generator to
  the spectrum analyzer
• Stage freq 0 Hz
• Stop freq 20 MHz

10
Signal measurements (Steps 16)

• Reduce the VBW
• Notice the noise is much lower

11
Signal measurements (Step 16 cont.)

• Set the threshold to be above the noise floor

12
Signal measurements (sine wave)

• Measured frequency and amplitude

13
Signal measurements (Triangle waveform)
14
Signal measurements (Square waveform)
15
Noise floor
16
Noise floor

• In RF applications, 1 mW is often taken as the
  reference standard and dBm is used to indicate
  this standard.
• This level of -174 dBm is referred to as the
  noise floor or minimum noise level that is
  practically achievable in a system operating at
  room temperature. It is not possible to achieve
  any lower noise unless the temperature is lowered

17
Noise floor

• Note

18
Noise floor

• The noise floor is a function of frequency as
  shown in this and the next 2 slides.
• For example, the measured amplitude at 1.8 GHz
  is 90 dBm

19
Noise floor

• The measured amplitude at 3.29 GHz is 79 dBm

20
Noise floor

• The measured amplitude at 99.75 GHz is 85 dBm