Quads for Fun
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November, 2016 News
Receivers
This piece usually comes build in the drone or comes with the transmitter when purchased. Some types of transmitters are only compatible to their own receivers brand. There are exceptions to be paired with other receivers but pay attention on that issue. Currently, transmitters use the band 2.4GHz, DSS (digital spread-spectrum) protocol in two different types FHSS and DSSS.
FHSS (Frequency-Hopping Spread-Spectrum): transmits within a specific frequency band but changes the precise frequency of the transmission hundreds of times a second trying to reach interference immunity.
DSSS (Direct Sequence Spread Spectrum): uses random PN code sequences and picks one or more pseudo randomly selected frequencies out within the band. With several randomly selected frequencies, along with random code sequences, it's very unlikely all of them would ever experience interference at the exact same time, also trying to achieve interference immunity. There are other band modulation methods used for RC aircrafts like AM, FM/PPM and PCM. All these modulations use narrow band radio transmission. They transmit a signal on a specific frequency within the radio spectrum. Pilot needs to tune into an exact same specific frequency both, receiver and transmitter. RC métier uses radio frequencies in the 27 to 75 MHz range. Most hobby grade RC aircraft use the 72 & 75 MHz band range of the radio spectrum.
AM: the first method used for controlling RC models. It sends information to the model by changing the amplitudes of carrier wave at a specific frequency. The receiver then filter the highs and lows of the changing amplitudes of the carrier wave into usable information. But this method is easily affected by almost any electrical noise and much interference issues occurs.
FM & PPM (Frequency Modulation and Pulse Position Modulation) methods on RC market belongs to 80’s. FM sends information by changing the frequency of the radio wave instead of the amplitude. However, the Quad itself can generate electrical noise and the receiver can interpret this own noise as a true signal causing, in the worst cases, aircraft control loss.
PCM (Pulse Code Modulation) works by embedding a digital signal within the FM radio wave. A chip build in the RC transmitter will encode a digital transmission and send it out as a FM wave. The receiver decodes that digital data back into an analog signal. Experts say that PCM method have a fail-safe feature. If the receiver doesn’t understands the radio signal it will move automatically the servos to throttle off and all other controls to neutral. It’s not a feature like fail-safe-landing executed by Quads with GPS. But it will helps keeping control of the aircraft.
Examples: DJI Naza, Walkera GPS-04, Ublox NEO-6M, GS407 Helical, 3DR uBlox, YS S4 Serie