Third Order Intermodulation Distortion Performance Test

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

Two signals separated by 100 kHz are combined in a directional bridge or directional coupler (for isolation) and are injected into the analyzer input. The analyzer measures the amplitude of the lower and upper distortion products. TOI is computed using the higher (worst case) of these two products.

Below 3.6 GHz low pass filters are used to attenuate the source second harmonic. The harmonic is filtered so it does not create a false failure.

The filtered source is turned on and the signal level is measured at the splitter output port with a power meter. The filtered source amplitude is measured on the analyzer. The unfiltered source is turned on and its amplitude is measured on the analyzer using the analyzer’s delta-marker feature. The amplitude of the distortion product is then measured relative to the unfiltered source amplitude.

Required Test Equipment

Test Equipment

Recommended Model Number1

Microwave signal generator #1 and Microwave signal generator #2

PSG models
(see main equipment list)

Power meter

N1914A

Microwave power sensor

N8485A CFT

Power splitter

11667B

Directional bridge

86205A

Directional coupler

87300C

Attenuator, 10 dB fixed

8493C Option 010

Low pass filter, 50 MHz

Telonic Berkeley TLA 50-5AB2

Low pass filter, 1.8 GHz

  • 2 required

RLC L-1636

Cable, BNC (m) to SMB (f)

8121-2063

Cable, BNC (m) to BNC (m)

8120-2582

Cable, Coaxial, 3.5 mm (m) to 3.5 mm (m)

  • 3 required

11500E

Adapter, BNC (m) to 3.5 mm (f)

1250-1700

Adapter, Type-N (m) to BNC (f)

1250-1476

Adapter, 3.5 mm (m) to Type-N (m)

1250-1743

Adapter, 3.5 mm (f) to Type-N (m)

  • 2 required

1250-1744

Adapter, 3.5 mm (m) to 3.5 mm (m)2

  • 2 required

83059A

Adapter, 3.5 mm (f) to 3.5 mm (f)

  • For 3.5 mm source
  • 2 required

83059B

Adapter, 2.4 mm (f) to 3.5 mm (f)

  • For 2.4 mm source
  • 2 required

11901B

Adapter, 3.5 mm (f) to Type-N (m)

  • For the 8485A power sensor

08485-60005
  1. Refer to the main equipment list for a list of alternative models (if available).
  2. The 3.5 mm (m) to 3.5 mm (m) adapter between the power splitter and the DUT is critical in this test. Proper connector care and torqueing practices must be followed in order to insure optimal performance.

Connection Setups

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