On 20 May 2005 at 8:08, mike wilson wrote: > The only Eric I know is Eric the half-a-bee. At the moment, it's a very tired > Subaru Forester.
I know I should have got a smack in the chops for that but I couldn't resist. > Thanks for the links. There's a very useful one for a detector that uses LEDs > to show what frequencies are whizzing around. At the moment we are using a > combination of heterodyne detectors that have to be tuned to the frequency. > In > practice, you can use a frequency that will pick up some noise from most bats > but you will likely miss the rarer or quieter (which is our present problem) > species. What are the frequency ranges of the varieties of bats that you wish to detect? I assume that you are using a heterodyne type detector to down-shift their chirps to audible frequencies? Sounds like the heterodyne receiver needs a set of pre-set selectable oscillator frequencies, maybe if it cycled between pre- sets you would have a better chance? A broad-band ultrasonic transducer connected to several narrow pass band filters each driving an indicator could be used for quick species identification if their emission frequencies are sufficiently narrow-band. > It's beginning to look like using an infrared video camera will be the best > solution, even though it is going to add a lot of time to each job. But we > get > paid for our time, so.... I would guess that most video cameras or still P&S type digital cameras could be fairly easily modded to optimise their IR sensitivity. The following page shows how to rip out the IR/AA filter in a couple of cameras: http://www.jr-worldwi.de/photo/index.html?modding.html Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://members.ozemail.com.au/~distudio/publications/ Pentax user since 1986, PDMLer since 1998
