Spread-Spectrum Radios Hop Across 900-MHz Band

May 12, 2007
These frequency-hopping radios provide high-speed wireless data to a wide range of industrial applications, operating at low power in the unlicensed 902-to-928-MHz band.

Spread-spectrum technology has long provided the military with secure communications. For almost as long, it has also fueled the growth of FreeWave Technologies (Boulder, CO), a leading supplier of long-distance, high-data-rate radios to military applications as well as customers in the oil and gas industries, the electric power industry, automated manufacturing, and even golf courses. The firm's latest series of frequency-hopped spread-spectrum radios operate in the Industrial-Scientific-Medical (ISM) band of 902 to 928 MHz with as much as 1-W transmit power for a line-of-sight, point-to-point range as great as 60 miles.

These radios can operate in a number of allocated bands, including the 900-MHz, 2.4-GHz, and 5.8-GHz bands. FreeWave's FRGplus and FGRHT radios (see figure) make effective use of the available bandwidth allowing users to balance their requirements for operating range and data rates with secure communications that are also energy efficient.

The FGRplus combines a sensitive receiver with a robust transmitter, using 128-b data encryption to reinforce the security provided by the company's proprietary spread-spectrum technology. The radio operates from 902 to 928 MHz with receiver sensitivity of –110 dBm for a bit-error rate (BER) of 1 X 10–4 at 115 kb/s and –106 dBm for BER of 1 X 10–4 at 153.6 kb/s. The receiver selectivity is 20 dB at ±230 kHz of the center frequency. The receiver features 140 dB system gain.

The transmitter runs with output power levels from 5 mW to 1 W using two-level Gaussian frequency-shift-keying (GFSK) modulation. The radios use a total of 112 hopping channels, with 105 total user-selectable hopping patterns or 15 patterns per band across a total of 7 user-selectable hopping bands. The efficient scheme occupies only 230.4 kHz of bandwidth at any one time for data throughput to 154 kb/s.

The FRGplus employs 32-b CRC error correction to ensure reliable operation even under adverse environmental conditions. The radio consumes less than 140 mA at +12 VDC in full-time receive mode and less than 550 mA at +12 VDC in transmit mode.

The FGR-HT radio trades some operating range for data throughput. It has a maximum point-to-point clear line-of-sight distance of 40 miles and point-to-multipoint range of 15 miles, but the maximum data throughput is a generous 867 kb/s. With total system gain of 129 dB, the radio's receiver has sensitivity of –102 dBm for a bit-error rate (BER) of 1 X 10–4 at 614 kb/s and –96 dBm for BER of 1 10–4 at 867 kb/s. The FGR-HT radio also provides transmit levels from 5 mW to 1 W with two-level GFSK modulation.

Both the FRGplus and FGR-HT are designed to operate at voltages from +6 to +30 VDC. Both radios measure 165 X 74X 59 mm and weigh 427 g.

FreeWave Technologies, 1880 S. Flatiron Court, Suite F, Boulder, CO 80301; (800) 548-5616, (303) 444-3862, FAX: (303) 786-9948, e-mail: [email protected], Internet: www.freewave.com

About the Author

Jack Browne | Technical Contributor

Jack Browne, Technical Contributor, has worked in technical publishing for over 30 years. He managed the content and production of three technical journals while at the American Institute of Physics, including Medical Physics and the Journal of Vacuum Science & Technology. He has been a Publisher and Editor for Penton Media, started the firm’s Wireless Symposium & Exhibition trade show in 1993, and currently serves as Technical Contributor for that company's Microwaves & RF magazine. Browne, who holds a BS in Mathematics from City College of New York and BA degrees in English and Philosophy from Fordham University, is a member of the IEEE.

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