|
Thanks Andy! David Bartsch > Date: Fri, 19 Feb 2010 13:40:25 -0500 > From: andy.goldstein@videoray.com > To: personal_submersibles@psubs.org > Subject: Re: [PSUBS-MAILIST] Passive sonar research > > David, > > The basic idea is that you can mix (multiply) the high frequency signal > with another sinusoid. This has the effect of creating two new > signals. This is shown by the trigonometric identity Sin(a)*Sin(b) = > 1/2 * Sin(a-b) - 1/2 * Cos(a+b). > > So you now get two side bands at the difference and the sum of the two > frequencies. You can then filter out the sideband you dont want. In > this fashion you can move the desired frequency into audible range. > Bandwidth considerations aside. > > The process is called Heterodyning and there are tons of web sites. > > If you are doing it digitally you can play other tricks like resampling > at a different freq. or other multirate techniques. > > Quick google gave: > http://www.stanford.edu/~omeri/Detection%20and%20Conversion%20of%20Ultrasonic%20Frequencies.htm > > -a > > > Jon Wallace wrote: > > > > David, > > > > Do an internet search for "bat detector" or "listening to bats" or use > > similar wording. Somebody out there has a schematic for a home-built > > bat listening device. I've seen it before but didn't keep a reference > > to it. It detects the ultrasonic "pings" of bats looking for food at > > night. This will save you from having to reverse engineer an existing > > device. As I recall, the circuit is minimal and quite simple. > > > > Jon > > > >> > >> I was able to locate a kids toy that could detect and allow the > >> listening to bats. Perhaps if I took this simple device apart, I > >> could modify it to detect slightly higher frequencies I so desire. > >> > >> > > > > > > > > > > ************************************************************************ > > ************************************************************************ > > ************************************************************************ > > The personal submersibles mailing list complies with the US Federal > > CAN-SPAM Act of 2003. Your email address appears in our database > > because either you, or someone you know, requested you receive messages > > from our organization. > > > > If you want to be removed from this mailing list simply click on the > > link below or send a blank email message to: > > removeme-personal_submersibles@psubs.org > > > > Removal of your email address from this mailing list occurs by an > > automated process and should be complete within five minutes of > > our server receiving your request. > > > > PSUBS.ORG > > PO Box 53 > > Weare, NH 03281 > > 603-529-1100 > > ************************************************************************ > > ************************************************************************ > > ************************************************************************ > > > > > > http://www.videoray.com > > > > > ************************************************************************ > ************************************************************************ > ************************************************************************ > The personal submersibles mailing list complies with the US Federal > CAN-SPAM Act of 2003. Your email address appears in our database > because either you, or someone you know, requested you receive messages > from our organization. > > If you want to be removed from this mailing list simply click on the > link below or send a blank email message to: > removeme-personal_submersibles@psubs.org > > Removal of your email address from this mailing list occurs by an > automated process and should be complete within five minutes of > our server receiving your request. > > PSUBS.ORG > PO Box 53 > Weare, NH 03281 > 603-529-1100 > ************************************************************************ > ************************************************************************ > ************************************************************************ > Hotmail: Trusted email with powerful SPAM protection. Sign up now. |