The 2.4GHz Industrial Scientific and medical (ISM) radio band has the advantage of reduced interference from other radio sources so reducing glitching, particularly when used in conduction with DSM.
DSM (Digital Spectrum Modulation) technology is based on an optimised version of Direct Sequence Spread Spectrum. DSM and DSM2 technologies provide users with pure digital control, providing an impenetrable radio link that is immune to interference. There are two main broadcast methods that spread spectrum manufacturers can utilise. One format is called Frequency Hopping Spread Spectrum (FHSS). With an FHSS system, the transmitter transmits a narrow band signal and rapidly jumps from one frequency to the next, spending a few milliseconds on each frequency. However, engineers discovered that FHSS had several limitations that would prevent it from being the optimal solution for RC. While more difficult and costly to develop, engineers began experimenting with Direct Sequence Spread Spectrum (DSSS) and optimised the modulation scheme to overcome critical response and re-link issues. DSSS systems transmit on a single selected frequency but on a very wide band. Only a small portion of that band is used for specially encoded information. In addition, DSSS offers an increase of processing gain for significant improvements in range.
An updated version of DSM technology referred to as DSM2 (second generation protocol) is now available. With DSM2, the total latency of the radio system has been greatly reduced, while the bit-rate has been increased. When combined, these improvements provide a faster and more locked-in feeling when compared to traditional 27MHz, 72MHz, or 75MHz radio systems. DSM2 also provided a new opportunity when separating the two receivers. By providing superior path diversity, the DSM2 receiver can now see a broader RF environment.
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