I have used both PC's and notebooks with A/D cards, some from NI and some from other manufacturers. If you need multiple channel samples, you have to watch out for inter-channel sampling rate, for which some cards have larger time intervals than others. The fix then is to get a simultaneous sample-and-hold, which samples all channels at the time the first one is sampled (freezing the samples on all the others) and then fills the multiple channel buffers at a rate faster than the interval between within channel samples. Noise can be controlled by using differential input; this provides effective noise cancellation but cuts the number of available channels in two (typical 8 channel cards are only 4 channel differential). A/D cards now can sample at mega-samples per second, but these are often only available in PCI internal card format. PCMCIA cards continue to improve in performance.
I suggest using USB2 or Firewire removable drives since these are much faster and larger capacity. The problem with removable disks is that they generally need more power than a notebook can provide. Also, many notebooks use low rpm drives -- 4400 or 5400 rpm -- and this slows their performance. Depending on the notebook, you can replace the internal disk with a faster and larger one.
As has been pointed out, many "Sound Cards" have issues associated with acquiring signals in the audio spectrum. These issues include low-frequency drop off, capacitor input (assumes signal is AC), and other "features" that make audio sound acceptable to our ears but may alter the basic signal. As a rule, A/D cards make no such compromises; their job is to record anything from DC to the Nyquist limit of their sampling rate and induce nothing on the signal amplitude.
Rugged notebooks are available, but the ruggedness add thousands of dollars to the price. These models can take being dropped and immersed and exposed to dust without much concern. The issue of power remains an issue. On boats or vehicles you can carry extra batteries. In fixed spots you can set up solar/battery systems, but when you have to travel light, then the CF memory recording systems will be the winner.
Mike Macaulay [EMAIL PROTECTED]
Michael C. Macaulay, Sr. Oceanographer Applied Physics Laboratory, University of Washington 1013 NE 40th St., Seattle, WA 98105-6698 206-543-7105; FAX 206-543-6785; [EMAIL PROTECTED]
