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Performance Levels and Methods of Measurement of Electromagnetic Radiation from Vehicles and Devices Narrowband, 10 kHz to 1000 MHz
The SAE J1816-1987 standard is a foundational document for electromagnetic compatibility (EMC) testing in the automotive and device industries. It defines methods for measuring incidental narrowband electromagnetic radiation in the frequency range of 10 kHz to 1000 MHz, and establishes performance levels to protect nearby communication and broadcast receivers. This article provides an overview of the key requirements, measurement equipment, test setup, and common considerations for engineers implementing this standard.
🛠️ Engineering Insight: The standard is analogous to FCC Part 15 but adapted for vehicles and large devices. It focuses on narrowband emissions (as opposed to broadband in SAE J551) and provides a common test method for repeatability across different test sites.
Measurement Equipment and Antenna Setup for Narrowband Emissions
The standard specifies measuring equipment conforming to CISPR Publication 16 or ANSI C63.2. To ensure repeatability between test sites, antennas must be selected based on the frequency range. The following table summarizes the required antennas:
| Frequency Range | Antenna Type |
|---|---|
| 10 kHz – 30 MHz | 1.1 m monopole with ground plane, and a loop antenna (enclosed in a 60 cm square) |
| 30 MHz – 200 MHz | Broadband biconical dipole |
| 200 MHz – 1 GHz | Log-periodic dipole array (max length 1.2 m) |
Key setup parameters include:
- Polarization: The electric field antenna shall be vertically polarized. The loop antenna is used for magnetic field measurements in three orthogonal planes.
- Antenna Height: The reference point (ground plane of monopole, midpoint of biconical or log-periodic elements, or center of loop) shall be positioned at 1.0 ± 0.1 m above the ground plane.
- Measurement Distance: The test antenna shall be placed at 3.0 ± 0.1 m from the test vehicle or device, measured from the center of the antenna elements (or tip for log-periodic) to the perimeter of the device.
⚠️ Common Mistake: Using incorrect antenna polarization is a frequent error. The electric field must be measured with vertical polarization; horizontal polarization may be considered in future revisions but is not part of this standard. Additionally, for magnetic field measurements, the loop must be oriented in three orthogonal planes to capture the full emission.
Test Procedures and Performance Levels for Receiver Protection
The test procedure requires equipment calibration and positioning the vehicle or device adjacent to the antenna. Long-term operator-controlled devices (e.g., blower motors) should be set to maximum noise-producing conditions, which may require running the engine for some subsystems.
Detector Types and Bandwidths: Measurements shall use a peak or quasi-peak detector. The standard specifies the following bandwidths depending on frequency and detector type:
| Frequency Range | Quasi-Peak Bandwidth | Peak Bandwidth |
|---|---|---|
| 10 kHz – 150 kHz | 200 Hz | 1 kHz |
| 150 kHz – 30 MHz | 9 kHz | 10 kHz |
| 30 MHz – 1 GHz | 120 kHz | 100 kHz |
The established performance levels are intended to protect adjacent mobile communication and broadcast receivers. The standard covers narrowband emissions from on-board logic and computer modules. For broadband emissions, reference is made to SAE J551. Outdoor free-space conditions are the reference; indoor shielded rooms should be correlated to open site measurements.
🛠️ Design Insight: To ensure repeatable results, pay careful attention to ground plane size and antenna positioning. The monopole requires an appropriate ground plane. For measurements at lower frequencies (below 30 MHz), near-field interactions can affect results; using the specified antennas and setup minimizes variability. The loop antenna should be completely enclosed by a 60 cm square to maintain a defined measurement geometry.
Indoor vs Outdoor Test Site Correlation
While open site measurements are satisfactory, anechoic or shielded rooms are desirable at higher frequencies to reduce ambient signals. At low frequencies, standing waves can occur even in anechoic rooms. It is essential to establish correlation between indoor and outdoor test sites, with free-space (outdoor) as the reference condition. For more details on anechoic shielded rooms, see SAE J5107.
Frequently Asked Questions
- What is the main purpose of SAE J1816-1987?
It provides a common test method for measuring narrowband electromagnetic radiation from vehicles and devices, establishing performance levels to protect communication and broadcast receivers. - Which antennas are used for different frequency ranges?
Monopole and loop antennas for 10 kHz–30 MHz, biconical dipole for 30–200 MHz, and log-periodic dipole array for 200 MHz–1 GHz. - How does this standard relate to FCC Part 15?
SAE J1816 is analogous to FCC Part 15 methodology but adapted specifically for vehicles and large devices. It uses similar detector types and bandwidths. - Is vertical polarization always required?
Yes, for electric field measurements in this standard. Horizontal polarization may be considered in future revisions.
