Articles

Introducing the New DSM System from Spektrum

10/20/2004 by

Copyright:© 2004 Horizon Hobby, Inc.

Print This Article Bookmark This Article
Share This Article

In this article...

Page 1: Advancing RC
Page 2: How DSM Works
Page 3: Spektrum FAQs

AM, FM, PCM and now DSM. Spektrum’s newly released DSM (Digital Spectrum Modulation) system advances RC radio technology to the next generation. Based on an optimized version of Direct Sequencing Spread Spectrum, DSM offers pure digital control providing an impenetrable radio link that’s immune to all types of interference. And with 4096 bit resolution and 5.6ms response time, the DSM system offers seemingly infinite accuracy and instantaneous response for a totally connected driving experience.

WORLD’S MOST SECURE RADIO LINKS

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 now Spektrum offers this technology for your RC car’s radio system.

SPEKTRUM'S DSM TECHNOLOGY

In development for over four years, Paul Beard, a leading engineer in the Spread Spectrum industry, designed Spektrum’s DSM system. The DSM system utilizes Direct Sequencing Spread Spectrum technology that has been optimized for RC car use. Unlike current narrow band 27 and 75MHz systems, Direct Sequencing Spread Spectrum or DSSS generates a wide signal on a single frequency, and information is encoded with its own Globally Unique Identification number (called GUID) such that the receiver only recognizes the information from its specific transmitter. And with over 4.2 billion available GUID codes, it is virtually impossible for a receiver to be controlled by anything other than its mating transmitter. Spektrum calls this optimized form of modulation DSM–Digital Spectrum Modulation.


DSM SYSTEM SPECIFICATIONS

  • Frequency Band 2.400–2.4835GHz
  • Channels 79
  • Channel Spacing 1MHz
  • Range 3000 ft
  • Latency 5.6 ms
  • Resolution/Channel 4096 steps

DSM RECEIVER VB SPECIFICATIONS

  • Weight .40 oz/ 11.3 g
  • Dimensions (LxWxH) 1.62x 1.06x.57”/ 41.2x 27.0x 15.3mm
  • Input Voltage 3.2–9.6V
  • RC Channels 3
  • Current 40 mA @ 4.8V
  • Antenna Length 8.5 in

ULTRA HIGH FREQUENCY ADVANTAGE

John Adams, Horizon’s Engineering Manager, headed up the R+D on the Spektrum ™ DSM Spektrum project. Paul Beard of California’s Silicon Valley was the inventor of DSM technology.

The Spectrum DSM system operates in the ultra high 2.4GHz ISM (Industry, Science and Medical) band. This ultra high frequency offers several advantages over conventional 27 and 75MHz systems. First, all model-generated radio interference from noisy motors, speed controllers, bad bearings, metal-to-metal noise, etc. exists below 300MHz. At 2.4GHz (that’s 2400MHz) the operational frequency range of the Spectrum system is 8 times higher than the range of this model-generated RF noise, making the system immune to these types of interference. Secondly, 2.4GHz is an internationally accepted band, so it’s 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 8.5” and can be cut down to 3.6” if desired, making antenna mounting within the body easy. The transmitter antenna is a mere 3.5” long, eliminating the “fishing rod” that normally extends into view.

FCC learned valuable lessons from other bands and applied those lessons to the 2.4GHz band. And unlike the 27 and 75MHz band, the FCC limits the power output in this 2.4GHz to a maximum of 1watt, thus preventing other 2.4GHz systems from overpowering each other. In other words, there are no “high power” commercial users interspersed in the 2.4 GHz band.

THE BENEFITS OF DSM

Spektrum’s DSM system eliminates all types of radio interference, including model-generated noise from motors, ESCs, bad bearings, etc. and from outside sources like pagers, cell phones, wireless computer systems and other RC radio systems, and offers these benefits:

  • No more waiting for an open frequency—just turn it on
  • Ultra fast 5.6ms response time
  • No tuning or maintenance to perform (ever)
  • Built-in fail-safe drives servos to preprogrammed position if signal is lost
  • Ultra precise 4096 bit resolution
  • Operates on international 2.4GHz ISM band so no need to change bands when traveling to international races
  • Short 8.5” or 3.6” receiver antenna length and 3.5” transmitter antenna length
  • 40% less current draw with the transmitter means 40% more battery life
  • Telemetry ready for rpm/speed, temperature, battery voltage, lap times and signal strength
  • Legal for most racing organizations including ROAR, NORRCA and IFMAR
  • Available for most popular 3-channel module radio systems for easy, inexpensive conversion to DSM technology


FHSS VS. DSSS

There are two primary types of Spread Spectrum technology— 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-based 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.

While more difficult and costly to develop, our engineers began experimenting with Direct Sequencing Spread Spectrum and optimized the modulation scheme to overcome critical response and re-link issues. In addition, 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 use and Spektrum’s DSM system was born.