[SOLVED] Finding the way of doppler signal

[logicpro9999]

I have a stereo signal coming from a car towards a radar and I want to understand is the car closing in on radar or is it moving out of radar. How to understand this just looking at the stereo signal? Signal has sine and cosine components.

 

[kripacharya]

I have a stereo signal coming from a car towards a radar and I want to understand is the car closing in on radar or is it moving out of radar. How to understand this just looking at the stereo signal? Signal has sine and cosine components.

what sort of signal is this ? Is this stereo as broadcast on FM radio ? On TV ?

The 'normal' radars work on microwave freqs of around 5-10 GHz (if memory serves me right), and it bounces its own signal from the vehicle. So its not clear what you mean by stereo for a radar.

Secondly - its not clear what you mean by sine & cosine. ANY signal can be thought of as a combination of sines & cosines. So do you mean the stereo signal has sine on one channel, and cosine on the other ? Or what ??

Does the receiver also know the original frequency of this sine and cosine ?? or not ?

Lastly, if you actually mean that we are doing Offset Carrier Demodulation, or quadrature demodulation or sideband filtering of the received signal, then the answer is Yes - we can determine the direction of movement

 

[logicpro9999]

Yes we are doing quadrature demodulation and want to find direction of movement? How is it done?

 

[kripacharya]

Yes we are doing quadrature demodulation and want to find direction of movement? How is it done?

i thought as much. Why didn't you write this in the first place ?
There are many articles/ writeup/ papers on this topic - just google for "quadrature doppler direction"

here are a few:

**broken link removed**
**broken link removed**
https://radiographics.rsna.org/content/23/5/1315.full

 

[floopz]

Subtract the received signal from the original signal (downconvert) to find the difference if they are coherent or use a long fft to find the shift. If the new signal is shifted up in frequency, it is closing (blue Doppler). If it is down in frequency is is receding (red Doppler). Try to think of the sound of a race car as it closes in towards you and zooms past. It increases in frequency then falls back down after Closest Point of Approach.