Advancing RC with Spektrum Radios
AM, FM, PCM and DSM. Spektrum's DSM (Digital Spectrum Modulation) system continues to advance RC radio technology to the next generation. Based on an optimized version of Direct Sequencing Spread Spectrum, DSM offers pure digital control by providing an impenetrable radio link that is immune to all types of interference. And with 4096 bit resolution and 5.6ms response time, the DSM system offers infinite accuracy and instantaneous response for a totally connected driving experience.
For the highest security levels of radio communications, NASA, the U.S. military, and government agencies like the CIA and FBI rely on Spread Spectrum technology. Whether guiding unmanned reconnaissance aircraft over enemy territory, controlling satellites in space, or communicating critical mission orders to the battlefield, the impenetrable secure link that Spread Spectrum coding provides makes it ideal for these decisive security applications. And only recently, Spektrum offers this technology for your RC car, truck, airplane, and helicopter radio systems.
Spektrum's DSM Technology
The DSM 2.4GHz system (Digital Spektrum Modulation) uses Direct Sequencing Spread Spectrum technology that has been optimized for R/C Industry use. Unlike the current narrow band 27 and 75 MHz systems, Direct Sequencing Spread Spectrum or DSSS generates a wide signal on a single frequency and information is encoded with it's own Globally Unique Identification number (GUID) such that the receiver only recognizes the information from its specific transmitter. With over 4.2 billion available GUID codes, it is virtually impossible for a receiver to be controlled by anything other than its bonded transmitter. Spektrum calls this optimized form of modulation DSM–Digital Spectrum Modulation.
The Spectrum DSM system operates in the ultra high 2.4GHz Industry, Science, and Medical (ISM) band. This ultra high frequency offers several advantages over conventional 27 and 75MHz systems. Model-generated radio interference from noisy motors, speed controllers, bad bearings, or metal-to-metal noise exists below 300MHz. At 2.4GHz (2400MHz) the operational frequency range of the Spectrum system is 8 times higher than the range of this model-generated RF noise, which makes the system immune to these types of interference. Also, 2.4GHz is an internationally accepted band, so it is not necessary to change radio equipment when traveling to overseas events. And because the 2.4GHz wavelength is very short, the required lengths of the antennas are much shorter. The receiver antenna is usually around 8.5" and can be cut down to only 3.6" if desired, making antenna mounting easy. The transmitter antenna is a mere 3.5" long which allows hobbyists to scrap the "fishing rod" that normally extends out.
FHSS vs. DSSS
Two primary types of Spread Spectrum technology exist - Frequency Hopping (FHSS) and Direct Sequencing (DSSS). FHSS systems transmit a narrow band signal and rapidly jump from one frequency to the next spending a few milliseconds on each frequency. 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. Originally, Spektrum engineers started their development with FHSS systems because they were relatively easy and inexpensive to develop. However, it was soon discovered that FHSS had several limitations that would prevent it from being the optimal solution for RC.
Though more difficult and costly to develop, Spektrum's engineers began experimenting with Direct Sequencing Spread Spectrum and optimized the modulation scheme to overcome critical response and re-link issues. Also, DSSS offered 18dB increase of processing gain for significant improvements in range. With years of development and testing, the DSSS modulation scheme was optimized for RC car and air use - which is when Spektrum's DSM system was originally born.
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