Amateur Spread Spectrum

Paul Rinaldo, w4ri@amrad.org

Hal Feinstein, wb3kdu@amrad.org

André Kesteloot, n4ick@amrad.org

The use of spread spectrum communications began in the Amateur Radio Service in March 1981 when the FCC issued a Special Temporary Authority (STA) to AMRAD. W4RI and K2SZE made the premiere HF contact using frequency hopping. WA3ZXW, N4EZV, WB5MMB and K8MMO were also involved in these early experiments. A joint FCC-AMRAD 'fox hunt' demonstrated that spread spectrum stations could be located with direction-finding techniques. N4ICK became involved later, beginning in 1986.

At AMRAD's urging, in 1985 the FCC amended Part 97 of its Rules to permit regular spread spectrum communications in the Amateur Radio Service with certain restrictions as to spreading methods and limited to frequencies above 420 MHz. These restrictions have been the subject of controversy within the Amateur Radio community ever since, some desiring to remove them entirely including permitting spread spectrum operation on all amateur bands, others wishing to tighten them. STAs subsequently have been issued to K6KGS and a number of amateur stations on the West Coast, and in 1996 to the Tucson Amateur Packet Radio Corporation (TAPR), both of which allow operation above 50 MHz with unrestricted spreading codes. In 1996, the American Radio Relay League (ARRL) petitioned the FCC to permit other spreading sequences, require automatic power control when transmitting at powers above 1 watt, while keeping the lowest operating frequency at 420 MHz. The FCC has issued a Notice of Proposed Rule Making and is expected to decide on rule changes during 1997-98.

What is Spread Spectrum?

Spread spectrum is a technique to reduce the power density of a radio transmission by spreading its signal over a wide band of frequencies, at least 10 times the information rate and usually much higher. Under some conditions, reduction of power density permits greater spectrum sharing opportunities than using the traditional access method frequency- division multiple access (FDMA) or even time-division multiple access (TDMA). As the receiving system must despread the spread spectrum signal just the opposite from how it was originally spread and in exact synchronization, there is the added advantage of rejection of interference or jamming and immunity from frequency-selective fading. Some modern cellular and other systems use a form of spread spectrum called code-division multiple access (CDMA).

How Do I Learn More?

The best basic information on amateur spread spectrum can be found in The ARRL Spread Spectrum Sourcebook, authored by AMRAD, N4ICK editor, and published by the ARRL. Check their Web pages at http://www.arrl.org. Spread spectrum information also is found in the AMRAD Newsletter mailed to members.

How Can I Get Involved?

AMRAD welcomes participation in new developments in amateur spread spectrum. This includes, but is not limited to:

  • construction and testing of new spread spectrum radios
  • experimenting with spectrum sharing techniques
  • mainstreaming the use of spread spectrum in the amateur bands
  • writing for the AMRAD Newsletter
  • contibuting to future editions of The ARRL Spread Spectrum Sourcebook
  • supporting the modernization of Part 97 spread spectrum rules

The AMRAD Webmaster

Last modified: Sat Sep 22 21:50:04 EDT 2007