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Radar System

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demokesola

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Hi All,
I want to design a radar system with or without a display. (if without a display it should have a beeper that increases freqency as proximity to device gets smaller.

My Question:
1.Knowing that radar works on two basic principles: Echo and Doppler shift effect. at what frequencies of sound am i able to detect human presence?.

2. A friend says that i can also use Radio waves at high frequencies but i argue that EM field may not be able to detect human presence. Isn't this true.

If eventually i can't detect human What first things do i need to do to develop one that sees metal.

Thanks GURUs
 
sounds like someone watches alot of james bond.


you want to use radar to detect humans without a transmitter. good luck

one major problem yo are gone have is what makes the B-2 stealth so damn good. it is virtually impossible to bounce rf off an absorbent object.

not sure what yo uwant to do with it but i would start looking into FISH FINDER TECHNOLOGY.

good luck
 
Intrusion detection

Hi demokesola:

Both radar (electromagnetic waves) and ultrasonics (sound waves) are very commonly used for intrusion detectors, and both can do the job quite well. The body is a very satisfactory reflector for radar waves because it is full of water and conductive chemicals.

Radar intrusion detectors tend to be somewhat more expensive due to the technology involved. They normally operate on the doppler effect by which a continuous wave is transmitted and reflected waves are detected in the same cavity that forms the transmitter. If nothing in the field of view of the transmitter/receiver is moving, the jumble of reflected signals are all at the same frequency as the transmitted signal (no doppler shift) and, when mixed with the transmitted signal inside the transmitter cavity, there is no difference frequency and therefore, no audio frequency output.

If something in the field of view is moving (with a component of motion toward or away from the transmitter), the return signal is doppler shifted, there is a difference frequency created in the mixer in the cavity, and an audio frequency output results. This frequency of this AF output is directly proportional to the velocity of the moving object long the transmitted beam. For the commonly used frequency for intrusion detectors (about 24.5 GHz, I believe), I think the AF is about 30 Hz per mile per hour target velocity. (I use units of mph because I built one of these for vehicle speed detection many years ago.)

While it is possible to build something like this "at home" using a tin can as the radar cavity/antenna (google Ramsey electronic kits), it is much easier and wiser (from a safety and compliance perspective) to use ready-made radar modules consisting of a die-cast cavity with attached mini-horn antenna, complete with transmitter gunn diode and receiver/mixer diode. You just apply well regulated DC power and are handed the AF output on a platter. All your circuit work is at audio frequencies and, therefore, non-critical and simple.

For intrusion detection you don't normally care about MEASURING the velocity of the target. You just want to know if something is moving in the field of view. For that you just need a simple AF amplifier, rectifier, and threshold detector to activate a relay. This is just what is inside commercial radar intrusion detectors costing several hundred dollars (US). Just a few transistors or an op-amp, rectifier, and comparator required.

At the time I was experimenting with them, the complete transmitter/receiver modules were in the US$100 neighborhood, and several people were making them. At the time, I used modules by Amperex (the tube maker), but I think they are defunct. ALPHA had a pretty complete line of modules at one time. Don't know if they still exist, either.

Interestingly, 25 KHz and 40 KHz ultrasonic wavelengths are of the same order of magnitude as radar intrusion detector module wavelengths, and you can use a similar approach, as some makers of ultrasonic intrusion detectors do. You can also use a true radar-ranging approach, in which a very short burst of ultrasonic sound is transmitted and the time-of-flight for the return signal is detected. This is used for the architectural distance measuring devices you can buy in the hardware store. This approach is a little more complex to implement and is probably overkill for an intrusion detection scheme. At one time, National Semiconductor produced a chip to implemeent this ranging function. Look in their "special function ICs" section.

You can buy a matched pair of ultrasonic transducers from many surplus stores and catalog electronics outlets for a dollar or two. For these, you have to generate the ultrasonic frequency to drive the transmitter.

Googling, "ultrasonic intrusion detection," should keep you out of the bars for a while, with about 23,000 hits. "Radar intrusion detection" gives you about 81,000 hits.

Have fun.

awright
 
ladar

Hi everyone,
I want to know details about ladar.......I've found out that transmitter emits laser and the receiver detects it which has to be ampified.....now what is to be done with that amplified signal in order to display speed......

what I've until now discovered is that the difference of the transmitted and received frequency has to do some job here.......
For each miles/hr the doppler shift is 7.76 Hz......
I'm new to this subject and wants to study it deeply.....Always waiting for quick replies.......
Don't think that it is my coarse work!!!.....I will ofcourse never ask anyone to do my coarse work......I saw this topic somewhere and got interested in it......
 
Time

=============
DEMOKESOLA:
==============
I recommend you use sound to detect people since air waves can never travel through solid objects. Low frequency signals also produce a much larger Dopppler shift than high frequency signals when the target is moving at low speeds. Read on to Awright's response to see why...and some little things about the math involved.

If your device is used outside where wind and distance degrade sonar, you might want to use radar. If you do your friend is right (and you are too). Long range communications use long radio waves which penetrate and travel further much more easily. If you use high frequencies, they penetrate much less (but I don't know how well they echo). Either, way use a high frequency in a non-restricted radio band to have the highest chance of detect soft mushy things such as people. I am unsure if people will bounce radio waves, but if radio does echo off people it will work better at outside at long ranges than sonar will (but sonar will still be able to detect lower speed targets more easily).

=============
AWRIGHT (I hope I wrote it well enough for you to understand. It's a good thing reading is easier than writing.):
============
The signal is just amplified to make it stronger because it is pretty weak when it gets back to you. Amplification makes it easier to detect and work with. After you receive the signal, you need a processor or circuit that measures the frequency of the incoming signal. Then you send that frequency to a microcontroller and have it do the following calculation based on what is said in my Physics textbook:

FR = [(v+vR)/(v+vE)]*FE

FR = receiver frequency
FE = emitter frequency
vR = velocity of receiver
vE = velocity of emitter
v = the speed of the wave (ie. speed of light or sound)

vR and vE should use the same sign convention for direction (ie. positive velocity means moving to the right, negative number means moving to the left).

This equation is very general and works for laser, radar, sound, or any other signal. I recommend sound because in the equation, a lower frequency signal produces a much larger Doppler shift when the target is moving at low speeds, so it is easier to build the circuitry.

The emitter can be called the target which echoes the signal back the signal depending on your scenario...but from the equation, it seems to me that the Doppler shift happens BOTH ways- while it is travelling to the target and when it is travelling back to you. In this case you would have to use the equation twice:

#1 Equation, Signal travelling to the target:
Emitter = your machine
Receiver = your target

#2 Equation, Signal returning to your machine:
Emitter = your target
Receiver = your machine

You have two equations with two unknowns- the velocity of the target and the frequency of the signal when it arrived at the target. You can use the two equations together to solve these two unknowns- solve for the frequency first and then use that to solve for the velocity of the target. Easy as pie!

Now that we've been talking about this stuff, I think I might actually use it for motion detection in my robot...none of this heat-seeking motioon type stuff! I want to detect rocks being thrown at my robot! it has never occured to me that Doppler Shift can be used for motion detection...it has always been for speed detection for me, but the I just never made the connection that movement = speed.
 
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I built a Ramsey doppler radar many years ago and it is possible to detect people moving the trouble is it is basically a TRF receiver and the noise can mask slow movement. Ramsey specs say 7hertz per mile per hour is the doppler shift.
 
Doppler shift depends upon the transmitted frequency....For 2.6 GHz case as in Ramsey it is 7.76Hz .....
 
Sorry that should have been TFR (tuned frequency radio)as well, I think.
I don't have the paper work that went with the kit but Iwas sure it was 1.5GHz operating frequency. I don't really care it worked, I did my experiments, and it now sits in the garage wait for the next inspiration.
I was trying to point out that a person moving at 4KPH/2.5MPH doesn't generate a lot of shift especially if the receiver is noisy.
Marconi did a lot of work in 70's with the British army to develop battlefield doppler radar systems for infantry, I don't know where that led.
 
I checked out the Ramsey site and found a PDF covering the SG-7 radar gun, so now I have some paperwork again and yes the frequency is 2.6GHz.
That suits something I might have planned for the radars use better anyway.
BTW anyone read "The radar war:Germany's pioneering achievement 1904-1945" by David Pritchard some very interesting doppler radar in there.
 
shadow_rider78 said:
sounds like someone watches alot of james bond.


you want to use radar to detect humans without a transmitter. good luck
It is possible to detect people, find weapons on people within crowds etc with passive millimetric radar which uses the energy radiated from a body.
Yes it is James Bond stuff and Yes it is being used today.
 
Hi Paul,
I don't want to detect humans....demokesola was trying to do that about 1 year back....I posted my question here by mistake.I should have started a new thread for it.....
I've seen the ramsey gun(it's transmitter,receiver and display schematics)....I wanted to know how laser can do the same work, done by microwaves in ramsey gun......So,I posted my question here....but the replies are not satisfactory for me....I know it has to do something with modulated laser but what and how ?and how to convert the doppler shift into displaying speed with logic circuits?One thing which is really troubling me is how can I get the doppler shift(transmitted freq-receiving freq.) in the circuit(As mixer has been used in the ramsey circuit)?
Plz help me with these questions....I don't want to detect humans........
 
yeah I've seen that too ..... but the description there is not answering to my questions....
 
demokesola said:
Hi All,
I want to design a radar system with or without a display. (if without a display it should have a beeper that increases freqency as proximity to device gets smaller.

My Question:
1.Knowing that radar works on two basic principles: Echo and Doppler shift effect. at what frequencies of sound am i able to detect human presence?.

2. A friend says that i can also use Radio waves at high frequencies but i argue that EM field may not be able to detect human presence. Isn't this true.

If eventually i can't detect human What first things do i need to do to develop one that sees metal.

Thanks GURUs

It depends where you're going to be using it. If you're going to be using it inside a building or room, then you can count on getting a continuous radar signal back from the walls (especially if they're metal), and you can just look for "holes" in that signal when a person comes in.

If you want to do it that way, go with a wavelength (and transmit power) of radar that is obviously safe to use around humans, but also is readily absorbed by water. That would probably be the easiest way to do it, although you couldn't get distance, you'd just get a "something's in here, at approximately 120 degrees from North (or some set point)" return.
 
MNA said:
yeah I've seen that too ..... but the description there is not answering to my questions....
Yes the transmitter doesn't seem to be connected to the rest of the circuit. Since the transmitter is free-running maybe the receiver locks to the transmitter, can't say I've studied it that closely. Maybe I'll build one and see what happens!
 
OK, after some quick cct browsing it looks like the 74AS04 is made into 2 osc, 1 transmit and 1 receive, I haven't done the figures but the transmit side looks asymetrical ie longer on/off. The receiver diode output goes HIGH when active.The receiver with the AND wired as non-inverting buffer thru the series resonate cct (which would also delay the signal) then mixed with an inverted (non delayed) signal would produce very brief pulses. This would go The output is then fed to an integrator and that signal fed thru a comparator into an AND gate with the receive osc. 74AS160 BCD DECADE COUNTER being clocked by the local osc until a pulse from the receive cct. I'll have to have a look in my OLD data books for the 74AS160 to get a better understanding. I don't like the timebase but it is cheap and so long as you don't have to take the results to court and you can calibrate it somehow, it could be fun.
 
ALERT, I have just seen an ad for the Mattel Hot Wheels Radar Gun for AUS$30, I have googled looking for some better description but to no avail.
I therefore can't say if it's optical or RF but since it's designed to be aimed at very small cars maybe optical.
 
Paul Obrien said:
The receiver diode output goes HIGH when active.
The receiver diode is forward biased all the time, so the logic following it will do nothing.
 
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