Display Scale Fidelity Performance Test

This test verifies that the PSA meets the Display Scale Fidelity specification. The test compares a known external attenuation change to a signal level change on the PSA. The Scale Fidelity error is the difference between the known attenuation change and the measured signal change. Fixed attenuators are placed on each side of the step attenuators in order to reduce mismatch errors. This test is performed in two parts.

Part 1 —  Input Mixer level of -21 dBm to -75 dBm

The PSA input attenuator is set to 10 dB. The source is set to +10 dBm and the external attenuator is set to 19 dB. The resulting -25 dBm (-35 dBm at the mixer) input signal is measured and recorded as the reference. Next, the PSA input signal is varied from -11 dBm to -65 dBm (-21 dBm to -75 dBm at the mixer) by switching external attenuation. The difference between the reference signal and the measured signal is compared to the known attenuation change and the Scale Fidelity Error is calculated.

Scale fidelity below -75 dBm is not measured as noise becomes the dominant error factor, and noise averaging would greatly increase test times.

Part 2 —  Input Mixer Level of -14 dBm

The PSA input attenuator is set to 10 dB. The source is set to +10 dBm and the external attenuator is set to 26 dB. The resulting -25 dBm (-35 dBm at the mixer) input signal is measured and recorded as the reference. Next, the PSA input signal is set to -4 dBm (-14 dBm at the mixer) by switching external attenuation. The difference between the reference signal and the measured signal is compared to the known attenuation change and the Scale Fidelity Error is calculated.

This test requires step attenuator calibration data to obtain valid results. Make sure you enter the calibration data for the step attenuators that you're using. Please refer to the Equipment Calibration Data section in the N7800A TME Help for details on how to enter this data. You must enter the data for the following columns to obtain valid results: Attn(dB), Uncert(dB) and ReflSize.

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Required Test Equipment

Test Equipment

Model Number

Signal Source

PSG Models
(see equipment list)

1 dB Step Attenuator

8494G Option 001, H50

10 dB Step Attenuator

8496G Option 001, H50

Attenuator Driver

11713E

Attenuator Interconnect Kit

11716A 

3 dB Fixed Attenuator

8491A, Option 003, H33

6 dB Fixed Attenuator

8491A, Option 006, H33

10 dB Fixed Attenuator

8491A, Option 010, H33

Type-N Cable

11500C 

BNC Cable

8120-2582 

3.5 mm (f) to Type-N (f) adapter
(for E4440A/43A/45A Option BAB)

1250-1745

2.4 mm (f) to Type-N (f) adapter
(for E4446A/47A/48A)

11903B  

Connection Setup

Display Scale Fidelity Test Setup, Part 1

Display Scale Fidelity Test Setup, Part 2