Third Order Intercept Distortion Performance Test

This test measures the Third-Order Intermodulation distortion produced by two input signals, and computes the Third Order Intercept (TOI) point.

Two signals separated by 100 kHz are combined in a directional bridge, or directional coupler, and are input to the PSA. Mixing products will appear on the PSA above and below the two fundamental frequencies. These mixing products are Third Order products which are located at 2*F1-F2, and 2*F2-F1, where F1 < F2 . The PSA measures the amplitude of the lower and upper distortion products relative to the fundamental frequency. TOI is computed using the higher amplitude mixing product.

Testing begins by turning on one signal source and measuring the signal level at the splitter output with a power meter. The other splitter output is connected to the PSA input. The signal amplitude is measured on the PSA. The second signal source is turned on and its amplitude is adjusted to match that of the first signal. The distortion products are then measured relative to the fundamental amplitude. The Intercept point is calculated as: TOI = Mixer Level + Distortion (dBc)/2.

In the 3 Hz to 3 GHz band, a filter is used to attenuate signal generator second harmonic product (2*F1). If a low pass filter was not used, the source second harmonic would artificially increase the distortion product. Above 3 GHz, the analyzer provides internal preselection so the source does not require an external filter.

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Required Test Equipment

Test Equipment

Model Number

Synthesized Sweeper
(2 required)

PSG Models
(see equipment list)

Power Meter

N1914B

Power Sensor

N8485A 

Power Splitter

11667B

Directional Bridge

86205A 

Directional Coupler

87300B 

10 dB Attenuator

8493C (Option 010)

BNC Cable (2 required)

8120-2582 

3.5 mm Cable (2 required)

8120-4921

50 MHz Low Pass Filter

0955-0306

1.8 GHz Low Pass Filter
(2 required)

0955-0491

3.5 mm (f) to 3.5 mm (f) adapter 
(2 required)

83059B 

BNC (m) to SMA (f) adapter

1250-1700

Type-N (m) to Type-N (m) adapter

1250-1475

Type-N (m) to BNC (f) adapter

1250-1476

Type-N (m) to 3.5 mm (m) adapter

1250-1743

Type-N (m) to 3.5 mm (f) adapter 
(2 required, 3 required for Option BAB)

1250-1744

3.5 mm (m) to 3.5 mm (m) adapter
(2 required)

1250-1748

2.4 mm (f) to 3.5 mm (f) adapter

11901B 

2.4 mm (f) to 3.5 mm (m) adapter
(for E4446A/47A/48A)

11901D

3.5 mm (f) to Type-N (m)
(8485A adapter)

08485-60005

Connection Setup

Power Meter Calibration

Third Order Intercept Distortion Low Band Test Setup
(50 MHz Low Pass Filter)

Third Order Intercept Distortion Low Band Test Setup
(1.8 GHz Low Pass Filter)

Third Order Intercept Distortion High Band Test Setup