e the rebroadcast repeater signal, which is very close in frequency to the incoming satellite signal, yet at a much greater power level, could otherwise overload the input side of the repeater. If the Sirius repeaters were to operate in this fashion--that is, were to make use of the signal being broadcast from the satellite--then their receive antennas would have to track the satellites along their highly elliptical orbit in order to maintain isolation between transmit and receive circuits. This would be an expensive proposition. So instead, Sirius has elected to feed its repeater sites using commercially available capacity of geostationary communications satellites, which operate in a different frequency band (Ku-band), thus alleviating this problem. The future of radio Clearly, the satellite SDARS and the terrestrial IBOC are poised for a battle for listener's ears in the not-too-distant future. The long-term future of radio is a bit more complicated, though. For IBOC, iBiquity is already planning all-digital IBOC, which eliminates the analog signal altogether. This version represents the final phase in the transition from analog to digital services in the AM and FM radio broadcast bands. It would differ from the hybrid IBOC version by increasing the power in the IBOC digital sidebands and by replacing the analog signal with additional, lower-power digital sidebands. Among other things, these would support a lower-quality, but more robust, version of the main channel audio, which the system would blend to under adverse conditions (instead of to the analog signal). The advantages of all-digital IBOC are its higher overall bit rate, better coverage, and reduced interference with adjacent channel signals. Since all-digital IBOC will produce additional interference in the analog portions of adjacent-channel hybrid IBOC signals, however, iBiquity is recommending that all-digital service not be initiated until the marke...
