Cable and satellite television proved that consumers will pay for content despite free broadcast alternatives. Now, XM Radio and competitor Sirius are testing the same waters in a high-stakes game to deliver subscription satellite radio services that go beyond the AM/FM dial. Originally targeting drivers, the two have recently rolled out modular satellite radio receivers that go from the car to the home and even to portable settings.

As an illustration of the breed, the Delphi SkyFi XM Satellite Radio contains a base receiver unit that interfaces to adapters for car and home use. Additionally, a boom box adapter for standalone portable operation is available. Each adapter functions as a mechanical holster for the receiver and provides an interface to external antenna assemblies.

Two surface-mount circuit boards and a monochrome LCD panel comprise the major subsystems of the receiver, whose functions include audio interface, signal decoding and most-though not all-of the RF communications. The primary circuit board is enclosed in a cast-aluminum shield that also serves as a thermal enclosure. A lead frame protrudes from one edge of the shielded enclosure to interface with the secondary assembly, which handles user I/O, audio conversion and the antenna/adapter interface.

STMicroelectronics makes custom channel decoder and source decoder chips (the STA400 and STA450) for the receiver and a special-purpose microcontroller for signal decryption. Atmel supplies two additional microcontrollers that serve the user interface and digital radio chips. A Silicon Labs synthesizer and a Maxim VCO buffer provide frequency generation for downconversion of the received signal.

M/ACom is the source for the front-end low-noise amplifiers (LNAs), where gain control appears to be managed in concert with an RF detector from Analog Devices, also supplier of the IF/mixer subsystem ICs. Other chips include a stereo D/A converter from Cirrus Logic, a 16-Mbyte DRAM from Micron and a 32-kbyte SRAM from Alliance. Both car and home adapter kits have RF front ends behind the antennas, and are made up largely of discrete gallium arsenide transistors, though an RF Micro Devices' LNA is used in the home adapter.

There are two parallel receive paths-one for the satellite signal and a second for reception over XM's terrestrial repeater network, built to fill reception gaps and potentially localize content. Estimated cost of goods sold for the receiver is more than half of the $129.99 receiver price, although XM adapters have a more comfortable margin.

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