Hello All, I have been writing a chirp sonar program using a standard PC and soundcard. I have only been testing in air so far. The draft of a web page is at http://members.optushome.com.au/eddiema/projects/chirp/chirp.htm The program is known to have bugs which I won't have time to fix for sevaral weeks - but hey its free. If anyone is interested in building a cheap chirp sonar based on my program please email me. I will be offline for a week starting this friday. Eddie.m