RX
Receiver
Radio receiver (RX) is what receives the signal from the radio transmitter (TX) and tells the flight controller what to do.
TX Protocol
RX Protocol
Radio transmitter (TX)
Radio receiver (RX)
Flight Controller
TX Protocols are in most cases specific to brands:
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FrSky: D8, D16, LR12
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Spektrum: DSM, DSM2, DSMX
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FlySky: AFHDS, AFHDS 2A
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Futaba: FASST
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Hitec: A-FHSS
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Devo: Hi-Sky
RX Protocols, some of them are universal:
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PCM, PWM, PPM, SBUS
Some of them are specific ones:
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TBS: CRSF Crossfire
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Graupner: SUMD, SUMH
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FrSky: FPort
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Multiwii: MSP
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Flysky: IBUS
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JR: XBYUS
Receiver protocols define the process in which the receiver signals are processed and sent to the flight controller.
Each manufacturer has their different types of receivers.
A Receiver must be compatible with the Radio Transmitter that work with the same protocol.
Frequencies must also be the same on both Rx and Tx. For instance; a 2.4GHz Transmitter can only work with 2.4GHz Radio Receiver.
RX Size
Radio receivers come in a different sizes and shapes.
Smaller receivers are more convenient for smaller multirotors where mounting options for hardware is very limited.
Binding
Binding
A Radio Transmitter will only communicate with a Radio Receiver if the two are binded. This process might differ on specific receivers and radios. Please refer to the user manual of your specific Rx and Tx.
A Single Radio Transmitter can be bound to multiple different Receivers. At the same time, a single receiver can only be bound to a single transmitter, not multiple transmitters.
RX Antennas
Receiver antennas are usually attached by U.FL connectors.
Some RX come with two antennas to ensure the best reception.
Some receivers are built-in antenna.
To achieve the best signal reception
it is recommended to keep them at a 90 degree angle.
Construction of RX Antenna
RX antenna is made from a coaxial cable (coax).
Ouside layer is plastic skin for physical protection.
The next layer is grounded metal shielding that prevents noise getting in and signal getting out.
Insdie is a thin insulated wire, which is the active element receives radio signals via a specific frequency.
With a shorter antenna we will have more capacitance. Or a longer antenna we will have more inductance. The additional capacitive or inductive reactance will result in antenna performance degrade.
Recommend follow the length of the original antenna that comes with the receiver.
Length of the active element depends on the frequency and is exactly 1/4 of the wavelength for a specific frequency.
As am example, the wavelength for 2.4GHz transmission is 122mm. 1/4 = 30.5mm for the active element.
*The resonant frequency happens to be a quarter of the signal wavelength, where the inductance and capacitance in the antenna are equal and cancel each other out. At this point the received signal of this frequency is the strongest.
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DO NOT CUT any part of the receiver's antenna wire. Cutting the antenna will reduce range.
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Extend the antenna wire in the model as far as possible for maximum range. If coiling the antenna wire is required do not create sharp bends in the wire, a coil should make a smooth circle.
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Do not allow the antenna wire to extend outside the body without the protection of an antenna tube, or the antenna wire may get cut or damaged, reducing range.