Want to Fly Legally? Understand This Essential UAV Certification

In recent years, the explosive growth of the UAV market has been accompanied by rising safety and communication risks. my country has continued to increase its safety supervision of UAVs. Among them, SRRC certification, as a mandatory certification for radio transmitting equipment model approval, is crucial to the legal operation of UAVs. This article will focus on the technical indicators and testing procedures of SRRC certification to help practitioners clearly understand the certification requirements and testing methods.

SRRC certification overview
SRRC (State Radio Regulatory Commission) is the management agency for model approval of radio transmission equipment in my country. All UAV and other radio equipment sold and used in China must pass its certification. UAV has a dedicated wireless communication module to transmit images and telemetry data, so it is included in the scope of key supervision. According to relevant regulations of the Ministry of Industry and Information Technology, except for a few small devices with extremely low transmit power (micropower UAV), other civilian UAVs must obtain SRRC certification before they can be legally sold and used.

Key certification indicators

The core technical parameters of UAV SRRC certification focus on frequency band and transmission power.

frequency division

• 1430-1444MHz： This frequency band is used for downlink telemetry and information transmission links for civil unmanned aircraft. Among them, the 1430-1438MHz frequency band is dedicated to video transmission of police UAVs and helicopters, and other civilian UAVs should use the 1438-1444MHz frequency band.

• 2400-2476MHz： Within the 2.4G frequency band, micro civil unmanned aircraft communication systems can only use this frequency band for wireless transmission.

• 5725-5829MHz： Commonly used in 5.8GHz high-speed data transmission, such as wireless video transmission, Wi-Fi and other applications.

Power division

• According to China's radio management regulations, radio transmitting equipment can be divided into micropower short-distance equipment and non-micropower short-distance equipment according to transmission power.

• The transmit power of non-micropower short-distance equipment exceeds the limit of micropower equipment, and the transmission distance is longer. It may cause greater interference to other radio equipment and requires SRRC certification.

Key technical indicators

The technical requirements for non-micropower short-distance equipment are as follows:

Certification test cases

During the SRRC certification process of SU17 UAV, we conducted standardized testing for each technical requirement and generated a detailed quantitative data report. SU17 UAV adopts 2.4GHz(2400-2476MHz) frequency band for image and telemetry data transmission. In China, the 2.4GHz frequency band is divided into 13 channels. The center frequency interval of each channel is 5MHz, the channel bandwidth is 20MHz, and 22MHz is actually occupied, of which 2MHz is an isolation band.

Working frequency

The frequency band requirement of UAV is 2400-2476MHz. Use a spectrum analyzer to check the cutoff frequency point of the current channel. The test data is as follows:

According to the measured waveform of the channel, it is clearly seen that the channel bandwidth is 22MH. The reason why it is greater than 20MHz is also to consider the frequency difference interference between frequency bands.

Equivalent isotropic radiated power limit

Equivalent isotropic radiated power is the total power radiated by the device in space. For SU17, the EIRP value needs to be less than 20dBm。Experimental link data Antenna gain: 3dB, line loss: 0.5dB, so set offset to 2.5dB. The test data is as follows:

Equivalent isotropic radiation power spectral density limit

The equivalent isotropically radiated power spectral density is a key indicator for measuring the radiated power of wireless devices within unit bandwidth. The EIRPSD value of UAV according to micro-power short-distance management is not greater than 10dBm/MHz。Experimental link data Antenna gain: 3dB, line loss: 0.5dB. So set offset to 2.5dB. The test data is as follows:

frequency tolerance

Frequency tolerance refers to the maximum allowable deviation between the transmitting frequency and the assigned frequency of a radio transmitting equipment under actual operating conditions. The standard requires that the frequency tolerance is not greater than 20×10 -6, which can be understood as less than 20ppm. For 2.4G, the frequency tolerance range is 2400MHz±48KHz. The test data is as follows:

Calculate the center frequency frequency offset value:2412-2411.995MHz=0.005MHz=5KHz SU17 meets the certification index requirements.

Out-of-band transmit power limit

Out-of-Band Emission (OBE) is the useless transmission power generated by equipment outside the nominal operating frequency band (channel bandwidth). It is an important technical indicator to ensure that radio equipment will not cause interference to other systems outside the designated frequency band. The standard requires that the maximum equivalent isotropic radiation power spectral density at the upper and lower limits of the frequency used should not be greater than -80dBm/Hz. Need to convert:-80dBm/Hz=-30dBm/100KHz=-20dBm/1MHz The test data is as follows:

Actual measured out-of-band transmit power limit:-40dBm/100KHz, SU17 meets certification requirements.

Spurious emission limits

Spurious emission limits are discrete unwanted signals generated by equipment outside the nominal operating frequency band. Including: harmonics (such as second harmonic, third harmonic), parasitic oscillation (caused by circuit nonlinearity), etc. The test data is as follows:

Measured data 1: 30MHz-1GHz, meeting certification requirements.

Measured data 2: 1GHz-12.75GHz, meeting certification requirements.

Special frequency band emission limits

The frequency range of 2483.5-2500MHz and 2390-2400MHz is selected for the spurious emission limit test as an example. The test data is as follows:

2483.5-2500MHz

2390-2400MHz

interference avoidance requirements

The core goal of interference avoidance requirements is to ensure that equipment or networks work reliably in complex electromagnetic environments and avoid mutual interference with other systems. This test resulted in laboratory test feedback that SU17 meets the certification requirements.

Experience sharing

Through the testing of SU17 in SRRC certification, we have some precautions to share with you for the certification testing of UAV in the 2.4G frequency band.

• According to the frequency requirements of SRRC certification, UAV is allowed to use the 2.4G frequency band 2400-2476MHz. So the UAV industry can use channels 1-11.

• Under the 20MHz bandwidth, channel numbers 1/6/11 are preferred because they are all independent channels. The applicable scenarios are mainly high-density environments in the 2.4G frequency band. Taking advantage of the characteristics of multiple channels, interference can be reduced and stability improved.

• The preferred channel under the 40MHz bandwidth selects one of the main channels 3/5/7 to become an independent channel. The applicable scenarios are mainly low-interference environments, using wide bandwidth to increase transmission rates.