Noise Reduction Techniques

How to Set Averaging

Using Hardkey/SoftTab/Softkey

Using a mouse

1. Press Avg BW > Main > Averaging.

2. Enter the Averaging number.

1. Click Response.

2. Select Avg BW.

3. Select Averaging....

Average dialog box help

Average ON   Check to enable Averaging.

Average Factor   Specifies the number of measurements that are averaged. Range of 1 to 65536 (2^16).

Average Type

Sweep  Each data point is based on the average of the same data point measured over consecutive sweeps. When the number of sweeps = Average Factor, the averaging continues following the Sweep Averaging formula.

(Sweep) Restart   Begins a new set of measurements that are used for the average. Applies only to Sweep averaging - NOT Point.

Point   Each data point is measured the number of times specified by the Average Factor, and then averaged, before going to the next data point.  

• On subsequent sweeps, averaging is automatically restarted by measuring each data point again the number of times specified by the Average Factor.

• Because measurements occur quickly in the background, the Average Counter is NOT updated.

• Point averaging is NOT available in Gain Compression, or Noise Figure Apps.

Notes

• An Average Counter appears on the screen when Sweep averaging is selected, displaying the number of sweeps that has been averaged. The effect on the signal trace can be viewed as the Average Factor increases. This can assist in the selection of the optimum number of sweep averages. The Average Counter is NOT updated for Point averaging.

• Channel-wide scope- Averaging is enabled and the factor is set for all measurements in a channel. The Average counter is displayed for each channel.

• Calibration - Because averaging is a mathematical process that occurs after the raw measurement is made, averaging can be turned ON before or after calibration without invalidating the error correction terms. If averaging is ON before calibration, the measurement of calibration standards are averaged measurements. More time is needed to perform the calibration, but there will be less noise in the resulting error correction terms. Subsequent corrected measurements will also have less noise error. In addition, noise is further reduced by turning Averaging ON after calibration.

• Triggering is implemented separately from Averaging. For example, setting averaging factor to 4 has NO effect on the number of triggers that are required to achieve 4 sweeps or 4 data points.

• Unratioed measurements - Although averaging unratioed (single receiver) measurements is allowed, you may see unexpected results.

• The noise floor does not drop when averaging unratioed measurements as on ratioed measurements.

• Phase results may tend toward 0.  This is because phase measurements are relative by nature. Measuring absolute phase with a single receiver appears random. Averaging random positive and negative numbers will tend toward 0.

Sweep Averaging Formula

NewAvg = (NewData/n) + [OldAvg*(n-1/n)] 'where n = average factor

From the formula, you can see that data from the first n sweeps continues to be included in the results of subsequent sweeps. Its effect is increasingly smaller but never diminishes to zero.  For example, with n = 5, the average of the 5 sweeps is displayed. On the 6th sweep, you see 4/5 the average of the first 5 sweeps plus 1/5 the new sweep.

The effects of older data can be eliminated by clicking Restart.

Learn more about Averaging (scroll up)

How to set IF Bandwidth

Using Hardkey/SoftTab/Softkey

Using a mouse

1. Press Avg BW > Main > IF Bandwidth.

2. Enter the IF Bandwidth value.

1. Right click on the BW icons on the status bar.

2. Select an IF Bandwidth....

IF Bandwidth dialog box help

For M938x,

Right click on the BW icons on the status bar then select IF Bandwidth... to display the IF Bandwidth dialog:

IF Bandwidth  Specifies the IF (receiver) bandwidth. The value of IF bandwidth is selected by scrolling through the values available in the IF bandwidth text box. The IF BW is set independently for each channel.

The following IFBW values are common to all models:

1 | 2 | 3 | 5 | 7 | 10 | 15 | 20 | 30 | 50 | 70 | 100 | 150 | 200 | 300 | 500 | 700 | 1k | 1.5k | 2k | 3k | 5k | 7k | 10k | 15k | 20k | 30k | 50k | 70k | 100k | 150k| 200k | 280k | 360k | 600k | 1M | 1.5M | 2M | 3M | 5M | 7M | 10M | 15M

For the highlighted IFBW settings (1 MHz and above):

1. • 7 MHz to 15 MHz settings are available ONLY with DSP version 5.0 and above.

   • The primary use for IFBW > 600 KHz is for wideband pulsed and pulse profile measurements. They do NOT provide faster sweep speeds for non-pulsed measurements.

   • A slight shift (1dB or more) in Log Mag traces may be seen when switching in and out of these bandwidths.

   • Available in Step sweep mode only - NOT available in Analog sweep.

   Note: The IFBW is limited to 600 kHz when performing Swept IMD measurements even if the Wide IF path is selected.

IFBW Shape  Selects the digital filter (window) to apply to the time domain IF signal. The filter effectively "shapes" the signal before application of the DFT to help avoid discontinuities which add unwanted frequency content to the spectrum. Each filter has its own advantages and disadvantages.

Gaussian filter shapes have much lower side lobe levels than the standard VNA filters, and so measurements with them will be less sensitive to closely spaced signals. Normally, in standard S-parameters this is not important and these filters show no benefit. But in cases such as mixer measurements, they may reduce spurious responses when spurious signals are close to the main signal to be measured. They have already been implemented in the spectrum analyzer mode.

Standard - Legacy filter. This filter is the fastest, but has side lobes that rise to ~-32 dBc.

Gaussian - This filter takes longer to acquire a point but has no side lobes.

The following shows the Standard and Gaussian 100 kHz filters:

Reduce IF BW at Low Frequencies : This is the same as LF Auto BW.

OK  Selects the IF BW value shown in the text box.

Learn about IF Bandwidth (scroll up)

How to access Bandwidth settings

Using Hardkey/SoftTab/Softkey

Using a mouse

1. Press Avg BW > Main

1. Click Response.

2. Select Avg BW.

3. Select Bandwidth....

Bandwidth dialog box help

Noise BW is equal to the Resolution BW divided by the Vector Average factor. You cannot directly set the Resolution BW or Vector Average in a Modulation Distortion channel. Resolution BW is always set to its maximum value for the given signal chosen. Vector Average is automatically set depending on the Noise BW setting.

Auto - Check to set the Noise BW to its maximum possible value. This results in the fastest possible sweep but increases the noise floor. If Auto is checked, then the Vector Average is set to 1, resulting in the widest Noise BW.

The Noise BW is displayed in the Softkey and in the middle of the display x-axis annotation.

How to enable/disable LF Auto BW

Using Hardkey/SoftTab/Softkey

1. Press Avg BW > Main > LF Auto BW.

2. ON enables and OFF disables LF Auto BW.

VNA Model

Stop Frequency

N5241B
N5242B

N5221B
N5222B

N5244B
N5245B

N5224B
N5225B

N5247B

N5227B

N5234B
N5235B

N5249B

19 MHz

0.05

0.05

0.005

0.005

0.005

0.005

0.025

0.05

38 MHz

0.05

0.05

0.01

0.005

0.01

0.005

0.025

0.05

53 MHz

0.05

0.05

0.015

0.005

0.015

0.005

0.025

0.05

75 MHz

0.1

0.1

0.025

0.025

0.025

0.025

0.025

0.1

105 MHz

0.1

0.1

0.05

0.025

0.05

0.025

0.025

0.1

146 MHz

0.14

0.1

0.1

0.025

0.1

0.025

0.025

0.14

175 MHz

0.29

0.1

0.15

0.025

0.15

0.025

0.025

0.29

205 MHz

0.29

0.29

0.15

0.15

0.15

0.15

0.025

0.29

250 MHz

0.5

0.29

0.25

0.15

0.25

0.15

0.025

0.5

396 MHz

1

1

0.5

0.5

0.5

0.5

1

1

500 MHz

1

1

1

0.5

1

0.5

1

1

500+ MHz
and above

1

1

1

1

1

1

1

1

M983xA

How to set Trace Smoothing

Using Hardkey/SoftTab/Softkey

1. Press Avg BW > Smoothing > Smoothing ON|OFF.