Microwave radio systems carry voice, video and data information through the air without wires. The antennas need "line-of-sight" from one to the other because buildings, hills or trees can block the signal. Broadband systems can carry multiple T1 lines (1.544 Mbps), three T3 lines (44 Mbps) or an STM-1 signal of 155 Mbps. More reliable systems use frequencies and power assigned by a Federal Communications Commission license to operate without interference with any other system. Unlicensed radios operate in a frequency band assigned by the FCC, but can interfere with one another in congested areas.
Bandwidth and Modulation
The bandwidth specification of a microwave radio determines how much traffic it can transmit. The higher the bandwidth, the more traffic. Bandwidths can be up to 50MHz or more, with different modulation specifications developing digital or analogue signals for telephone company, industrial or military applications. The receiver's bandwidth and modulation specifications must match the transmitter's.
Transmitter Power and Frequency
Transmitter specifications include power and frequency. Microwave radios usually transmit under one watt, but can transmit up to 10 watts. The FCC assigns frequency bands for various uses within the microwave spectrum from 2GHz up to 300 GHz. The FCC requires microwave radios to transmit at or below their maximum power allowance and within 0.01 per cent of their assigned frequency.
The receiver sensitivity specification tells the lowest signal a digital radio can receive without causing an error about once a second. Rated in dBm (decibels referenced to milliwatts), the specification tells at what level the radio starts giving a BER (bit error rate) of one in 10 to the minus sixth power. Analogue receiver specifications identify stages of base-band quality as the signal reduces until it becomes unusable. Maximum receive signal means the most powerful signal the radio can receive without noise or damage.