How is doppler Osillation detected in a signal.
Thanks.
John Docherty
My email is no longer valid.
Doppler Ocsillation
Started by ●July 12, 2005
Reply by ●July 12, 20052005-07-12
docherty@onlink.net wrote:> How is doppler Osillation detected in a signal. > Thanks. > John Docherty > My email is no longer valid.Helioiseismology? by looking for frequency modulation in the signal. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●July 12, 20052005-07-12
Thanks. perhaps Helioiseismology for dummies is what i need. ill be specific.it is an audio signal mostly from 500 to1500 hz. there should be doppler oscillation of between 30 and 200 hz.should i take the mean frequency of the sound, then measure the change in this? more specificly can i determine the rpm of a windmill,fan or whatever by listening to its sound.
Reply by ●July 12, 20052005-07-12
docherty@onlink.net wrote:> Thanks. perhaps Helioiseismology for dummies is what i need. ill be > specific.it is an audio signal mostly from 500 to1500 hz. there should > be doppler oscillation of between 30 and 200 hz.should i take the mean > frequency of the sound, then measure the change in this? more > specificly can i determine the rpm of a windmill,fan or whatever by > listening to its sound.The amount of Doppler shift is a measure of radial motion; the frequency of the Doppler shift is the frequency of the oscillating material. Proper motion is not involved either way. The blades of a fan can change the reflection distance and introduce a Doppler modulation on a reflected beam. In the early 50s, I made a "hood ornament" that consisted of a pair of counter-rotating wind-driven pinwheels in front of a reflecting screen. The resulting Doppler indicated a speed of over 200 mph when I was going 60. That speed was so clearly ridiculous that I never got a ticket. Transmitters are illegal, but any group that wants to use radar can hardly object to a reflector. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●July 13, 20052005-07-13
I wouldn't think it should be a problem to tell rpm by listening to the sound of a wind mill. With knowing very little about sound and acoustics, I would say that filtering would be a good start. If your wind mill is only turning at 30-200 Hz and your seeing 500-1500 Hz then I'd say that you might have wind blowing on your microphone. Try foam, or buying a proper outdoor mic. Then BP filter and take a close DSP look at 30-200 Hz spectrum....you should see it. Thomas <docherty@onlink.net> wrote in message news:1121194752.524069.275310@g43g2000cwa.googlegroups.com...> Thanks. perhaps Helioiseismology for dummies is what i need. ill be > specific.it is an audio signal mostly from 500 to1500 hz. there should > be doppler oscillation of between 30 and 200 hz.should i take the mean > frequency of the sound, then measure the change in this? more > specificly can i determine the rpm of a windmill,fan or whatever by > listening to its sound. >
Reply by ●July 13, 20052005-07-13
Jerry Avins wrote:> [snip] In the early 50s, I made a "hood > ornament" that consisted of a pair of counter-rotating wind-driven > pinwheels in front of a reflecting screen. The resulting Doppler > indicated a speed of over 200 mph when I was going 60. That speed was so > clearly ridiculous that I never got a ticket. Transmitters are illegal, > but any group that wants to use radar can hardly object to a reflector. >Reminds me of a story I read when smaller police departments started using radar. Speeder demanded trial and challenged accuracy of radar. Prosecutor produced 'expert' witness who demonstrated calibration by reflection from a tuning fork. Defense claimed prosecutor had proved radar was unreliable as it was evident that guy holding tuning for was NOT going 60 MPH. Case dismissed. I always thought the story apocryphal, but I do believe it represents some early reaction to radar. But now you have me thinking. Could you have set it up such that Doppler said you were either standing still or perhaps going backwards?
Reply by ●July 13, 20052005-07-13
Richard Owlett wrote:> Jerry Avins wrote: > >> [snip] In the early 50s, I made a "hood >> ornament" that consisted of a pair of counter-rotating wind-driven >> pinwheels in front of a reflecting screen. The resulting Doppler >> indicated a speed of over 200 mph when I was going 60. That speed was >> so clearly ridiculous that I never got a ticket. Transmitters are >> illegal, but any group that wants to use radar can hardly object to a >> reflector. >> > > Reminds me of a story I read when smaller police departments started > using radar. > > Speeder demanded trial and challenged accuracy of radar. > > Prosecutor produced 'expert' witness who demonstrated calibration by > reflection from a tuning fork. > > Defense claimed prosecutor had proved radar was unreliable as it was > evident that guy holding tuning for was NOT going 60 MPH. > > Case dismissed. > > I always thought the story apocryphal, but I do believe it represents > some early reaction to radar. > > > But now you have me thinking. Could you have set it up such that Doppler > said you were either standing still or perhaps going backwards?The only way you can appear to be going backward is to radiate negative frequencies*. (That's not true, but it sounds good.) Most police radars, particularly the early ones, sense relative motion but not direction. What is actually detected is the beat between the CW oscillator (often a Gunn diode) and the return signal. Only a phase detector could distinguish direction, but a simple diode is used. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●July 13, 20052005-07-13
Richard Owlett wrote:> Jerry Avins wrote: > >> [snip] In the early 50s, I made a "hood >> ornament" that consisted of a pair of counter-rotating wind-driven >> pinwheels in front of a reflecting screen. The resulting Doppler >> indicated a speed of over 200 mph when I was going 60. That speed was >> so clearly ridiculous that I never got a ticket. Transmitters are >> illegal, but any group that wants to use radar can hardly object to a >> reflector. >> > > Reminds me of a story I read when smaller police departments started > using radar. > > Speeder demanded trial and challenged accuracy of radar. > > Prosecutor produced 'expert' witness who demonstrated calibration by > reflection from a tuning fork. > > Defense claimed prosecutor had proved radar was unreliable as it was > evident that guy holding tuning for was NOT going 60 MPH. > > Case dismissed. > > I always thought the story apocryphal, but I do believe it represents > some early reaction to radar. > > > But now you have me thinking. Could you have set it up such that Doppler > said you were either standing still or perhaps going backwards?The only way you can appear to be going backward is to radiate negative frequencies*. (That's not true, but it sounds good.) Most police radars, particularly the early ones, sense relative motion but not direction. What is actually detected is the beat between the CW oscillator (often a Gunn diode) and the return signal. Only a phase detector could distinguish direction, but a simple diode is used. Jerry ______________________________________________ * True story. One winter day in 1937, a sourpuss neighbor's service water pipe froze where it emerged from the ground in the garage. That was a common enough occurrence for most homeowners to know what to do: call the welder. He would attach one lead from his truck-mounted gasoline-powered arc-welding generator to the pipe, and the other to a nearby fire hydrant. Resistance heating soon thawed the ice. The standard fee was $5, half a month's apartment rent in that neighborhood in the Depression. Sourpuss balked at the amount, offering $2 instead. Without comment, the welder hollered to his assistant, "Reverse the current. Freeze it up again." Sourpuss paid. -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●July 13, 20052005-07-13
Jerry Avins wrote:> Richard Owlett wrote: > >> Jerry Avins wrote: >> >>> [snip] In the early 50s, I made a "hood >>> ornament" that consisted of a pair of counter-rotating wind-driven >>> pinwheels in front of a reflecting screen. The resulting Doppler >>> indicated a speed of over 200 mph when I was going 60. That speed was >>> so clearly ridiculous that I never got a ticket. Transmitters are >>> illegal, but any group that wants to use radar can hardly object to a >>> reflector. >>> >> >> Reminds me of a story I read when smaller police departments started >> using radar. >> >> Speeder demanded trial and challenged accuracy of radar. >> >> Prosecutor produced 'expert' witness who demonstrated calibration by >> reflection from a tuning fork. >> >> Defense claimed prosecutor had proved radar was unreliable as it was >> evident that guy holding tuning for was NOT going 60 MPH. >> >> Case dismissed. >> >> I always thought the story apocryphal, but I do believe it represents >> some early reaction to radar. >> >> >> But now you have me thinking. Could you have set it up such that >> Doppler said you were either standing still or perhaps going backwards? > > > The only way you can appear to be going backward is to radiate negative > frequencies*. (That's not true, but it sounds good.) Most police radars, > particularly the early ones, sense relative motion but not direction. > What is actually detected is the beat between the CW oscillator (often a > Gunn diode) and the return signal. Only a phase detector could > distinguish direction, but a simple diode is used. >OK. Because of my background I tend to think in terms of Spectrum Analyzers. Thus 'positive offsets == approaching' and 'negative offsets == leaving' and appropriately adding/subtracting from patrol car velocity. And as I wrote this I "realized error of my ways" ;} Which leads me to "think" [perish the thought;] Presume a moving patrol car with 'front' facing "radar device". Using *only* Doppler and patrol cars 'speedometer' is it possible determine speed of both an approaching and receding target? "gut" says yes. "thought" says no. am i missing something?
Reply by ●July 13, 20052005-07-13
Jerry Avins wrote:> > * True story. One winter day in 1937, a sourpuss neighbor's service > water pipe froze where it emerged from the ground in the garage. That > was a common enough occurrence for most homeowners to know what to do: > call the welder. He would attach one lead from his truck-mounted > gasoline-powered arc-welding generator to the pipe, and the other to a > nearby fire hydrant. Resistance heating soon thawed the ice. The > standard fee was $5, half a month's apartment rent in that neighborhood > in the Depression. Sourpuss balked at the amount, offering $2 instead. > Without comment, the welder hollered to his assistant, "Reverse the > current. Freeze it up again." Sourpuss paid.Cruel crewel Last winter I paid ~$60 for said service What's even worse, growing up in Upstate NY I should have known better and left faucet(s) dripping. I now reside in tropical SW MO ;]
