RTCA DO-160 – Section 21.0 – Emission of Radio Frequency Energy

These tests determine that the equipment does not emit undesired RF noise in excess of the levels specified below.

The notches specified in the radiated emissions limits are included to protect aircraft RF sensors operating frequencies.

Categories are defined in terms of location and separation between the equipment and aircraft radio antennas. As these parameters are widely linked to aircraft type and size, some examples are given with each category definition.

Category B

This category is intended primarily for equipment where interference should be controlled to tolerable levels.

Category L

This category is defined for equipment and interconnected wiring located in areas far from apertures of the aircraft (such as windows) and far from radio receiver’s antenna. This category may be suitable for equipment and associated interconnecting wiring located in the electronic bay of an aircraft.

Category M

This category is defined for equipment and interconnected wiring located in areas where apertures are electro-magnetically significant and not directly in view of radio receiver’s antenna. This category may be suitable for equipment and associated interconnecting wiring located in the passenger cabin or in the cockpit of a transport aircraft.

Category H

This category is defined for equipment located in areas which are in direct view of a radio receiver’s antenna. This category is typically applicable for equipment located outside of the aircraft.

Category P

This category is defined for equipment and associated wiring located in areas close to HF, VHF, or Global Positioning System (GPS) radio receiver antennas, or where the aircraft structure provides little shielding.

Category Q

This category is defined for equipment and associated wiring located in areas close to VHF, or GPS radio receiver antennas, or where the aircraft structure provides little shielding.

General Requirements

This section does not measure or control spurious signals conducted out of the antenna terminals of receivers or transmitters. That control should be specified in the equipment performance standard for that receiver or transmitter. Radio transmitters or receiver/transmitters must meet specified emissions requirements (including the selected frequency ±50% of the band of frequencies between adjacent channels) while in a non-transmitting or receive mode.

Note: Do not measure radiation emanating from antennas or, in the case of transmitters, any radiation on the selected frequency ±50% of the band of frequencies between adjacent channels while the transmitter is keyed and supplying RF to the load.

The equipment under test shall be set up on a ground plane and operated in accordance with the criteria in Subsection 20.3 sub-paragraph a and sub-paragraph b, parts 1, 2 and 5 with the following limitations and additions:

a. For radiated emission measurements as in Subsection 21.5, antenna spacing to the ground plane edge and the EUT spacing from the ground plane edge shall be maintained as shown in Figure 21-11.

b. Interference shall be measured using the peak detector function of the interference measuring equipment. Interference measuring instruments with selectable IF bandwidths (BW) may be used, and the selected BW must be the values given in Table 1.

c. Line Impedance Stabilization Networks (LISNs) shall be used as shown in Figure 21-6. Figure 20-1 provides technical data for a LISN.

d. Power return wires tied locally to the ground plane as noted in Section 20.3.a (6) are not tested.

e. The time constant of the peak detector must be lower or equal to 1/BW. Where applicable, video bandwidths shall be selected to be greater than or equal to the resolution bandwidth.

f. Longer dwell, sweep and measurement times than those shown in Table 1 may be necessary to detect time-varying emissions. Dwell times in Table 1 are associated with a potential rate of variation of approximately 60 Hz.

g. For emission measurements, the entire frequency range for each applicable test shall be scanned. Minimum measurement time for analog measurement receivers during emission testing shall be as specified in Table 1. Synthesized measurement receivers shall step in one-half bandwidth increments or less, and the measurement dwell time shall be as specified in Table 1. Larger receiver bandwidths may be used; however, they may result in higher measured emission levels.

NO BANDWIDTH CORRECTION FACTORS SHALL BE APPLIED TO TEST DATA DUE TO THE USE OF LARGER BANDWIDTHS.

h. Recorded data shall provide a minimum frequency resolution of 1% or twice the measurement receiver bandwidth, whichever is less stringent, and minimum amplitude resolution of 1 dB.

i. Amplitude versus frequency profiles of emission data shall be automatically generated and shall be continuous.

j. Data Required In Test Report – The test report shall include the following test setup and data items.

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