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Antennas for Remote Terminal Units (RTUs)


  • Antennas for Remote Terminal Units (RTUs)

    RTUs are essential for IoT applications particularly for certain vertical industries including factories, processing plants, power generation, and distribution facilities, etc. Cellular capability embedded into some of these RTUS allows for:
    • process automation and ease of monitoring;
    • reliable transfer of data through cellular IoT (C-IoT), 4G LTE, and 5G NR networks;
    • with various data I/O, integration of different sensors is also possible.
    Redlion has a good portfolio of devices for remote terminal gateways.

    Sample RTU connection with Redlion RTU

    The cellular signals need to be sufficiently strong to ensure the reliability of data transfers between a remote network and monitoring/control systems. The signal propagation environment matters: irregular terrain (e.g., hills, mountains, valleys, etc.), water bodies, buildings, foliage, in addition to conductors near the cellular transmitter/receivers (such as metallic objects) affect the signal attenuation or path loss which in turn affects the reliability of the signal.

    Diversity vs. MIMO

    In a multipath propagation environment where there is no direct line-of-sight but instead have multiple paths because of the obstructions described above, transmit/receive diversity or MIMO is important to improve the radio performance.

    Transmit/Receive Diversity: for transmit diversity, multiple transmit antennas are used at the transmitter to send the same signal thereby increasing the chances that it will be received by a receive antenna. For receive diversity, multiple receive antennas are used at the receiver to increase the probability of detecting the signal from a single or multiple transmit antennas. Typically, no space-time coding or other MIMO-coding is used to increase the diversity or coding gain of the multipath fading channel.

    MIMO: for MIMO, special coding is applied to the signals from the different transmit antennas to take advantage of the spatial domain to correct errors in the multipath fading channel. Both 4G LTE and 5G NR support various levels of MIMO using, for example, 2, 4, 8, 16, 32, 64, 128, 256, etc., antennas (of course the higher antenna count, also called massive MIMO, is only possible for millimeter-wave frequencies above 24 GHz because the size of the antenna is directly proportional to the wavelength of the signal – and these massive MIMO antennas will most likely be for base station and small cell devices for the near future). For better MIMO operation and to take advantage of multipath propagation, it is important to connect the number of antennas as the MIMO order and provide proper separation between the MIMO antennas (or proper isolation of the antennas) to take advantage of the spatial diversity in the multipath fading channel.

    To allow adequate separation of the MIMO antennas (and to avoid obstructions and other interference in the proximity of the antenna), one can use low-loss coaxial cables (for longer runs consider 600-series cables). For example, with an RTU in an enclosure, one can mount an external antenna on the wall near a window or outside the enclosure as shown below.

    An enclosure with an antenna mounted on top

    The figure above shows an example ANTMBSM388134B antenna in an example VA09-12-ORBIT enclosure (contact us for other options)

    Here are some popular antenna styles for connecting to RTUs:

    A cellular antenna for RTU applicationCellular antenna for RTU applicationCellular antenna for RTU applicationCellular antenna for RTU applicationCellular antenna for RTU application

    When connecting antennas mounted at different position say near a window or outside using a cable, consider using antennas with a higher gain (for signal concentration, and compensating cable attenuation) and low loss cables for example the 600-Series
    Type of Cable 100 ft cable at 600 MHz (Band 71) 100 ft cable at 3500 MHz (Band 48) 250 ft cable at 600 MHz (Band 71) 250 ft cable at 3500 MHz (Band 48)
    200-series cable Attenuation 8.9 dB 22.3 dB 22.2 dB 55.5 dB
    600-series cable Attenuation 2.3 dB 6.0 dB 5.6 dB 14.9 dB
    Note the longer the cable and the higher the operating frequency the higher the attenuation or signal loss.

    Contact a RfWeL Wireless signal improvement expert to learn more about how you can overcome your signal coverage problems on your remote monitoring project. You may also reach us at +1.480.218.1877 Option 2.
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