measuring distance between two cars using infrared circuits

Modulate the microwave pulse frequency. There are modulation schemes (a
quick ramp up in frequency, or chirp for example) that will allow the
detection of both range and speed from the reflected signal. The DSP
might get a little more expensive than what is needed for Doppler alone.
Click to expand...
'swhat I suggested earlier.
You don't need DSP though, WWII radar fused bombs used this technique, and
they did NOT have dsp! :)
 
On Sun, 23 Jan 2005 23:09:54 -0500, Dave VanHorn wrote:

Doppler or direct time of flight, is doing it the hard way.

Chirp the transmitter at some number of MHz/uS
The reflection, even at a few nS delay, will be your carrier frequency of
that number of nS ago (can't be anything else!) so, the mix frequency
product at the receiver, will be proportional the the distance.

Smooth the output a bit to eliminate jitter, and you're there.
Click to expand...

What you are describing is a linear FM homodyne radar. I believe this is
how the actual radars now available on some cars work. For a large variety
of reasons, I agree with you that this is the best way to do it.

Because you can transmit almost continually, you can get by with transmit
power in the milliwatt range.

--Mac
 
AIUI, the reflection from a single sweep can't give you Doppler. You would
like to keep the single sweep duration short enough so that the object
doesn't move much during the sweep.
Click to expand...
Chirp dosen't do doppler, it measures the distance.
So if you want rate of change of distance, you'll have to compare distances
over time.
 
On Thu, 27 Jan 2005 09:26:36 -0500, Dave VanHorn wrote:

AIUI, the reflection from a single sweep can't give you Doppler. You would
like to keep the single sweep duration short enough so that the object
doesn't move much during the sweep.

Chirp dosen't do doppler, it measures the distance.
So if you want rate of change of distance, you'll have to compare distances
over time.
Click to expand...
You cut a lot of relevant information from my post, and you dropped the
attribution.

As I said, a single chirp (AFAIK) can't give you any information about
target velocity, but if you look at the IF of a target in motion from
chirp to chirp, you can see that it shifts over time. This phase shift
between chirps can give you information equivalent to Doppler.

There are FFT-based techniques for estimating this "Doppler" accurately.

You may choose to not call it Doppler, but it is called Doppler by many
people.


--Mac
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top