Spread-spectrum technology was developed during World War II for the military, as a means of providing secure and reliable communications even in hostile environments. By 1980, the technology was approved by the FCC for use in industrial, scientific, and medical wireless applications in addition to military. The technology is now used for mission-critical and life-saving applications. There are a number of proprietary protocols and the standards-based protocols including Bluetooth and wireless local-area networks (WLANs), but it is still a staple of military radios, including the new IM Series of spread-spectrum original-equipment-manufacturer (OEM) radio modules from FreeWave Technologies (Boulder, CO). These board-level radio modules provide dependable links at distances to 20 miles using the frequency band from 2.372 to 2.400 GHz.
These cost-effective radio modules operate with transmitter output-power levels from 100 to 500 mW, resulting in the 20-mile range in clear, line-of-sight conditions. The radios occupy 230 kHz of bandwidth with user-selectable frequency-hopping patterns: each radio offers three user-selectable frequency-hopping-bands with 15 hopping patterns selectable per band from a total of 105 frequency-hopping patterns. A total of 75 to 80 user-selectable frequency-hopping channels are available. In spite of all this hopping (or because of it), the radios achieve receiver sensitivity of -105 dBm for a 10 -6 bit-error rate (BER) and -107 dBm for a BER of 10 -4.
The receiver selectivity is 20 dB at ±115 kHz of the center frequency and 60 dB at ±145 kHz of the center frequency.
As expected, the OEM spread-spectrum module uses the most energy when transmitting. It operates on voltage supplies from 9.5 to 30 VDC, drawing 400 mA from a 9.5-VDC supply and 150 mA from a 30-VDC supply when transmitting. When receiving, the current draw is 130 mA at 9.5 VDC and 60 mA at 30 VDC. The radios feature idle and sleep modes to conserve battery power, with current draw at 37 mA from a 9.5-VDC supply and 13 mA from a 30-VDC supply when in idle mode and 8 mA from a 9.5-VDC supply and 2 mA from a 30-VDC supply when in sleep mode. The modules are equipped with RS-232, RS-422, RS-485, or ttl data interfaces. They measure 127 × 60.96 × 15.49 mm, weigh 74.4 g, and are designed for operating temperatures from -40 to +75°C.
The firm recently introduced a series of 1.3-GHz mission-critical radio systems (see the cover story in the August issue of Penton's Military Electronics, available from www.mwrf.com/milelec). As with the IM Series modules, these radios feature 32-b CRC error detection and 115.2 kb/s data throughput while operating over a frequency range of 1350 to 1390 MHz with occupied bandwidth of 230 kHz. The maximum transmit power is 1 W (or as much as 5 W with an external amplifier) which delivers a clear line-of-sight operating range of 60 miles. The radios employ frequency-hopping spread spectrum but can also operate in fixed-frequency mode. They employ two-level GFSK modulation with receiver sensitivity of -110 dBm at a bit-error rate (BER) of 10 -6. The 1.3-GHz spread-spectrum radios run on operating voltages of 6 to 30 V at operating temperatures of -40 to +75°C. They measure 2.86 × 2.44 × 0.59 in. and weigh only 5 oz. The company, founded in 1993, offers a variety of commercial and military radio designs, including commercial 900-MHz board-level radio products, 2.4-GHz radios, and 1.4 Licensed Radio System (LRS) band systems. The military radios include narrowband designs from 225 to 400 MHz as well as the new 1.3-GHz radios.