RF noise figure measurements with the SVA1032X spectrum analyser

Introduction

Noise figure is an important measurement parameter in the process of microwave product development and production, and its measurement is an important element of noise measurement. This manual describes in detail the use of a spectrum analyser to measure noise coefficients with the Siglent SVA 1032X (9kHZ - 3.2GHz), including the filter response of the spectrum analyser, the derivation of noise coefficients, the calculation of cascaded output noise, etc.

Spectral analyser filter response - RBW

The following procedure is used to measure the filter response or shape factor of the resolution bandwidth. Knowledge of the form factor is useful when measuring the noise figure. The procedure covers the measurement of the form factor of 100, 1kHz and 10kHZ RBW; however, it can also be used for other RBW and frequency settings.

Setup for SA and signal generator

1. Connect the 10 MHz clocks together, regardless of which is primary or secondary.
With Siglent devices, the external clock is automatically recognised and displayed during operation.
Ensure that the connectors are clean and correctly tightened.

2. Connect the RF output to the RF input of the spectrum analyser.

3. Setting for signal generator:
Pout=-10dBm
RF=CW @ 1GHz
ALC=automatic

4. Allow at least 30 minutes or more for the warm-up phase.

5. Set up spectrum analyser

6. Freq=1GHz
Frequency step size=10Hz (repeat the process with 100Hz and 1kHz
step size for the following RBW/VBW settings).

7. Span=0Hz
Trigger=Freewheel
Points=751, not adjustable

8. RBW/VBW=100Hz (repetition for 1kHz and 10kHz)

9. Attenuator=automatic

10. Preamplifier=off

11. Reference level=0 dBm

12. Scale/div=5 dB

13. Detector=Pos Peak

14. Sweep mode → Sweep rule → Accuracy

15. Sweep time=automatic

16. Mark=centre of the sweep

Measuring the form factor

Switch the signal generator ON, set the RF output amplitude so that a value of -10 dBm is displayed on the spectrum analyser
Increase/decrease the frequency of the spectrum analyser in 10Hz steps and record the values.
Repeat this for other RBW/VBW settings and other frequency steps.

Fc	Frequency	Delta (db)	RBW/VBW
1 GHz		+/- 50Hz	100Hz
	Fc - 50 Hz	-2,95
	Fc - 40 Hz	-1,87
	Fc - 30 Hz	-1,07
	Fc - 20 Hz	-0,44
	Fc - 0 Hz	0
	Fc + 20 Hz	-0,44
	Fc + 30 Hz	-1,08
	Fc + 40 Hz	-1,87
	Fc + 50 Hz	-2,94

Fc	Frequency	Delta (db)	RBW/VBW
1 GHz		+/- 500Hz	1kHz
	Fc - 500 Hz	-3,0
	Fc - 400 Hz	-1,92
	Fc - 300 Hz	-1,08
	Fc - 200 Hz	-0,47
	Fc - 0 Hz	0
	Fc + 200 Hz	-0,49
	Fc + 300 Hz	-1,07
	Fc + 400 Hz	-1,91
	Fc + 500 Hz	-3,0

Fc	Frequency	Delta (db)	RBW/VBW
1 GHz		+/- 5kHz	10kHz
	Fc - 5000 Hz	-3,02
	Fc - 4000 Hz	-1,94
	Fc - 3500 Hz	-1,51
	Fc - 3000 Hz	-1,08
	Fc - 2000 Hz	-0,48
	Fc - 0 Hz	0
	Fc + 2000 Hz	-0,48
	Fc + 3000 Hz	-1,09
	Fc + 3500 Hz	-1,5
	Fc + 4000 Hz	-1,94
	Fc + 5000 Hz	-3,03