RF Noise Figure Measurements using Spectrum Analyzer Siglent SVA1032X (9kHz – 3.2GHz)

Spectrum Analyzer filter response – RBW

The following procedure is used to measure the filter response or resolution bandwidth shape factor.  Knowing the shape factor is useful when measuring noise figure.  The procedure will cover measuring the shape factor of 100, 1kHz, and 10kHZ RBW; however, this procedure can be used for other RBW and frequency settings.

Setup for SA and Signal Generator

1. Tie the 10MHz clocks together, does not matter which is primary or secondary.
   For Siglent equipment, the external clock is automatically detected and displayed in use.
   Ensure connectors are clean and properly torqued.
2. Connect RF output to RF input of spectrum analyzer.
3. Setup for Signal Generator:
   Pout = -10dBm
   RF = CW @ 1GHz
   ALC = auto
4. Allow at least 30 minutes or longer for warm-up time.
5. Set up spectrum analyzer:
6. Freq = 1GHz
   Freq step size = 10Hz (repeat with 100Hz & 1kHz step size for RBW/VBW settings that follow).
7. Span = 0Hz
   Trigger = free run
   Points = 751, not adjustable
8. RBW/VBW = 100Hz (repeat for 1kHz and 10kHz)
9. Attenuator = auto
10. Pre-amp = off
11. Ref level = 0dBm
12. Scale/Div = 5dB
13. Detector = Pos Peak
14. Sweep Mode → sweep rule → accuracy
15. Sweep time = auto
16. Marker = center of sweep

Measuring shape factor:

• Turn the signal generator ON
  adjust RF output amplitude for a -10dBm reading on the spectrum analyzer
• Increase/decrease the frequency of the spectrum analyzer by 10Hz steps and record values.
• Repeat for other RBW/VBW settings and other frequency step sizes.

Conclusion:  The shape factor for +/- 2.0dB is approximately 0.80 of the RBW