thanks for the help daniel!
here's an update: i changed the program to pause for 1 second before initially requesting data from the QT300, and voila! it's working.... well, at least something is. the weird thing is that the 16bit data returned from the QT300 is pretty much constant, no matter how near or far my hand is from the antenna. but i set a line in the program to time the length of the QT300's acquisition burst (ie, the time between when arduino grounds the REQ line, and when the QT300 says it's ready by grounding the DRDY line). despite the same data value being returned, the acquisition time changes just as you would expect it to - when my hand is near to or touching the antenna, it drops right down. when i move my hand away, the burst time increases again.
strange.
so, if anyone has experience using a QT300 and might know what the problem is here, i'd love to hear your thoughts. it's a bit beyond me!
if you want to see the raw data from 3 different test runs with different Cs (sampling capacitor) values - i poseted them on the QProx website forum - follow the link: http://www.qprox.com/forum/read.php?f=1&i=4748&t=4748.
i forgot to mention in my post there that the data is taken over a period of about 5 seconds, with me moving my hand from about 10cm away from the antenna to a point where it almost touches. sampling rate is about 8 samples per second.
jon.