tag:blogger.com,1999:blog-5096278891763426276.post4826920801737790288..comments2020-03-28T07:29:09.384+02:00Comments on absorptions: Misleading representations of discrete-time signalsOona Räisänenhttp://www.blogger.com/profile/08764440174916554983noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-5096278891763426276.post-27369286544078647402014-02-01T21:47:01.725+02:002014-02-01T21:47:01.725+02:00This is amazing! I found your page thru a link on ...This is amazing! I found your page thru a link on Slashdot, where you decoded GPS data from a helicopter. That is so far above and beyond "Off the GEEK scale" that I just have to stand and applaud... loudly!! :D<br /><br />This all reminds me of some Cool Edit "decoding" I did a few years ago. Someone who was into Phone Phreaking liked to make recordings of "Wrong Number" messages from overseas in the 1970's. Back then, most of those calls were relayed via SW radio. One message he posted had a high-pitched "monkey chatter" signal, which I recognized as speech patterns. With a little sleuthing, I determined that it was a single sideband signal, and was exactly 4Khz above the audio. High pass filter, then "ring modulate" the remaining sound with a 4khz sinewave... the voice was a news feed, describing the death of Jim Jones! I e-mailed the guy who posted it, and he was flabbergasted. :) As geeky as this is, I think you've gone far above and beyond. I respectfully bow to the far superior Geek. :) Willie...http://www.mymorninglight.org/hamnoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-58115471029515703812014-01-16T16:22:46.905+02:002014-01-16T16:22:46.905+02:00As an additional mathematical note: The pumping si...As an additional mathematical note: The pumping sine wave would be <br />sin(w t)*sin(W t) <br />where w is the fundamental frequency (close to the sampling rate) and W is the pumping frequency. But this can be rewritten as<br />1/2 (Cos((w-W) t) + Cos((w+W) t)).<br />If the second term then is above the threshold of the low pass filter, the pumping sine equals the Cos((w-W) t) at the slightly shifted frequency up to stuff eaten by the band pass.<br />Roberthttps://www.blogger.com/profile/06634377111195468947noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-18016899656954531602014-01-13T08:48:09.655+02:002014-01-13T08:48:09.655+02:00No, they are composite images. You would have to s...No, they are composite images. You would have to step up the sample rate first. The second picture is just a plot with similar colors.Oona Räisänenhttps://www.blogger.com/profile/08764440174916554983noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-42495228780835797142014-01-13T04:23:45.008+02:002014-01-13T04:23:45.008+02:00Are the second and third pictures from Audacity? ...Are the second and third pictures from Audacity? I was unable to make anything similar using Audacity's low pass filter.Anonymousnoreply@blogger.com