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I don't think it's cellular RF activity, rather fluctuations in the battery (or internal circuit load capacities) voltage due to load changes when periphreals that turn on and off (e.g. CDPD transmitter, my old tp500 floppy drive when the battery was low). Kinda like how a lightbulb dims when a A/C compressor kicks in. A good way to test the RF theory is to disconnect the PC Card and try transmitting from a regular CDPD phone close to your thinkpad. The pcmcia circuitry is speced to supply a maximum current load, do you have docs on how much the CDPD card uses? If it comes close or exceeds it, other components in the system (e.g. like a trackpoint calibration reference voltage) suffer. Rich Chong