NORDIC's nRFTM series (nRF401/nRF403/nRF903) wireless transceiver integrated chip integrates high-frequency transmit/receive, PLL synthesis, FSK/gmsk modulation and other circuits in a single chip, multi-channel switching, direct serial digital interface And without Manchester coding, it is one of the most integrated wireless data transmission products. It has few external components and low power consumption, which is convenient for design and production. Can be widely used in remote telemetry, wireless meter reading system, traffic management system, automatic alarm security monitoring system, car anti-theft monitoring, wireless keyboard / mouse / joystick / PDA, community / home / office / factory wireless network, remote control toys / robots Wait. The characteristics of nRF401/403/903 are listed in Table 1-41.
Application design assessment
Before starting the system design, the following preliminary assessments should be made for the overall solution.
1. Electromagnetic compatibility
The use of wireless products is subject to the radio regulations of the country (such as European ESTI, US FCC), which has restrictions on frequency bands, transmit power, duty cycle, channel bandwidth and other indicators. The nRFTM series of wireless transceivers use the international frequency band of ISM (Industrial, ScienTIfIC, Medical) with a transmission power of no more than 10 mW, so it can be used in most countries. However, the designer may require amplification at the output stage of the nRF device, which must be considered for compliance with local regulations.
2. Design transmission and reception distance
The energy loss (FSL) of an RF wireless link propagating in the free space of the visible range is calculated by:
Where: the input is the wavelength of the RF signal; R is the distance from the receiving end to the transmitting end; the FSL unit is dB.
As shown in Figure 1-133, the power distribution equation for the RF signal to propagate in the visible range is:
Where: SRX is the receiver sensitivity (dBm); GRX is the receiver (RX) antenna gain (dB); Grx is the transmitter (TX) antenna gain (dB); PTX is the transmitter RF output power (dBm).
From the equations (1 - 10) and (1 - 11), the theoretical transmission distance R≈l 500 m can be calculated.
However, in practical applications, the loss of the antenna impedance matching circuit at both ends should also be considered, the loss due to obstacles and multipath transmission in the transmission path, and the quality of the PCB board, the product casing and the human body.
influences. Some of these factors are closely related to the application environment. As a general rule of thumb, the transmission distance in the outdoor open space is about 1/2 of the theoretical calculation distance, and the indoor transmission distance is about 1/10 of the theoretical distance.
It can be seen from Figure 1 - 134 that for every doubling of the RF frequency, the loss will increase by about 6 dB, which causes the transmission distance to decrease by a factor of two. So if the main indicator required by the designer is the transmission distance, then the lower frequency can be chosen. The use of relay transmission is also a method to effectively increase the communication distance.
3. Other factors
Since wireless transmission is prone to interference and is easily interfered by other noises, designers must also carefully consider the application and installation location, and do not blindly pursue long distances. For battery power, you can use the duty mode to save power.
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