Connect with us

Build functioning radar?

Discussion in 'General Electronics Discussion' started by Solidus, Jun 19, 2011.

Scroll to continue with content
  1. Solidus

    Solidus

    349
    4
    Jun 19, 2011
    Would it be feasible (and economical) to build a form of scanning radar as a DIY project?

    I've done a fair amount of googling on the subject and my results range from hacking apart a microwave to cannabalizing a Hotwheels toy.

    Is such a feat possible on a last-year-of-high-school/college kid budget? (I'm not trying to build a SAM radar unit, just something that could maybe have a max range of 30 or so feet.

    Thanks
     
  2. davenn

    davenn Moderator

    13,654
    1,888
    Sep 5, 2009
    Hi
    welcome to the forums :)

    scanning radar. ?

    just clarify, are you wanting to just determine the speed of a moving object? like the el-cheapo hotwheels radar "gun" does. or are you wanting to try and copy a radar system that has the rotating antenna and determine the direction and distance to an object... like used at an airport for aircraft, or weather radar ?

    just for your info, the term RADAR is for RAdio Direction And Ranging ..... ie. direction and distance

    the meaning gets a little blurred when referenced to police speed radars etc

    cheers
    Dave
     
  3. Solidus

    Solidus

    349
    4
    Jun 19, 2011
    Dave,

    I'm actually referring to the rotating assembly that typically scans for aircraft and what not. Obviously with such short range, I wouldn't be picking up aircraft, but more movement and anomalies in positions.
     
  4. davenn

    davenn Moderator

    13,654
    1,888
    Sep 5, 2009
    ok, cool, I have also wanted to play with something like that for years too but preferably something that would work over up to say 50km. I have the RF transmitter and receiver gear up in the microwave frequencies to do it.

    What I found and you will too, is the processing of the reflected signal onto a screen is the difficult part. Its going to require some serious hardware and software signal processing.

    The very early, and by todays standards, radar of late WWII, was extremely basic it would show "blips in a baseline (time for sending of pulse to reception of reflected pulse) on a screen that was calibrated in miles along the horizontal axis. They couldnt show height or any other info. Too many objects in the field of view just showed clutter and made the system unuseable.
    The british exploited that failing by dropping plane loads of "chaff" strips of tinfoil that were a 1/2 wavelength at the radar freq and that just filled the screen with 1000's of garbage signals.

    an early radar screen looked like this (from wiki).....
    see how you just get a vertical blip for the object

    [​IMG]

    here's the wiki link for radar, there's some wonderful maths involved ;)
    Radar

    without all that wonderful signal processing, you are not going to achieve anything more than the above. Even that is going to take some very accurate timing ccts.
    ponder this

    1) radio wave travels at 300,000km metres / sec
    2) with receiver turned off , you have to pulse the transmitter briefly say 1mS
    3) then turn receiver on in time to see the pulse but not be overloaded by the original transmitted pulse.
    4) using electronics or software, calculate the time difference between the time of the TX pulse and the reception of the reflected signal (echo).
    5) then display those results on some sort of screen in a useable way

    an object at 1km will have a return echo time of 1000m / 300,000,000m = 3.33 x 10 -6 S. an object at say 30 m (100ft) the time to receive the echo is going to be so so tiny

    Remember that for a radio signal to do the round trip to the moon and back is ~ 3 seconds

    cheers
    Dave
     

    Attached Files:

    Last edited: Jun 20, 2011
  5. Solidus

    Solidus

    349
    4
    Jun 19, 2011
    Dave,

    When you say you have the microwave RF gear that can handle that, what does that entail?

    I also saw the wiki page earlier, and it raises some fairly interesting questions. Could a radar 'mimic' be created using ultrasonic pulse electronics instead of the standard magnetron/microwave frequency devices conventional radar systems use?

    There are several videos on YouTube where people used ultrasonic transceivers mounted to a USB ported logic board and a (usually self-) coded application.

    ^ I see what you mean. You'd most likely have to have a software interpreter, those travel distances are too small to be calculated (or even noticed, for that matter) by human skill.

    And in regards to directional aspects of the scanning, would it be feasible to implement an element that detects the position of the assembly motor? In which case a software logger would plot that on a polar graph with respect to the orientation of the entire device, and the position with respect to the radius R would simply be the ratio of the distance D in terms of the distance at which you scaled the graph (pos. = D/R)

    How does this sound for a start?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,412
    2,780
    Jan 21, 2010
    Sure can. Think SONAR.

    It's pretty easy to get 40kHz acoustic transmitters and receivers (essentially speaker and microphone) and they're quite commonly used in distance measuring applications.

    Since sound only travels at 330m/s, your circuits have a lot longer to do their stuff and timing is now several orders of magnitude easier.
     
  7. Solidus

    Solidus

    349
    4
    Jun 19, 2011
    Oh wow. Haha, I was not even thinking along those lines.

    And how much ranging would that setup be able to accomplish (what would you project as the maximum effective distance)?

    Also, how much clutter/interference would you expect at 40kHz transmission?
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,412
    2,780
    Jan 21, 2010
    The issues remain pretty much the same as RADAR.

    Maximum distance is dependant on power (reflected power), receiver sensitivity (and noise) and time between pulses.

    Minimum distance is limited by how fast your receiver can recover after seeing the transmitter's signal, and the duration of the transmitted signal.

    Both have to consider multi-path effects and signal attenuation over distance.

    Have a look at some real world devices and see what they can achieve. A quick google shows a project that claims 5cm to 3 metres with +/- 3cm resolution.
     
  9. Solidus

    Solidus

    349
    4
    Jun 19, 2011
    And is that largely due to the similar design principles inherent in each?

    By changing the frequency, could different results be obtained (differing levels of traffic)?
     
  10. davenn

    davenn Moderator

    13,654
    1,888
    Sep 5, 2009
    Thanks for chiming in steve, work and home commitments stopped me from replying earlier. Ultrasonics was going to be one of my suggestions :)

    Solidus, have a look in maybe some of the large hardware stores etc and look for ultrasonic distance measuring units. They are handheld and about the same size as a packet of cigarettes.

    changing frequency, changes the resolution of the system. That is the system's ability to distinguish 2 objects close together. the higher the freq, the shorter the wavelength and therefore the smaller the objects that can be distinguished.

    cheers
    Dave
     
  11. poor mystic

    poor mystic

    1,066
    31
    Apr 8, 2011
    I believe it's possible to make a lidar without using lasers. The technique relies on a monchromatic light source which is reflected from the target object. Dual slits (a la Young) at the detector interfere and flash as the reflective target moves. A second dual slit 1/4 wavelength separated allows the lidar to detect the sense as well as the amount of movement, ie you can tell whether the object is approaching or departing.
    With red light this technique gives a half-wavelength resolution of better than 400nm.

    PS I have added an attachment which shows the technique in use in a microphone.
    I confess that the technique has not yet been tried.
     

    Attached Files:

    Last edited: Jun 20, 2011
  12. Solidus

    Solidus

    349
    4
    Jun 19, 2011
    Dave,

    I'm not too familiar in ultrasonic freqs, but is it possible to obtain a unit <500kHz?

    What sort of resolution would you need to distinguish, say a 5' 9 (~1.7m) tall person at say 50-60 feet (alternatively 20m)?

    (On a side note, sorry, this is the US, meters are an unfamiliar unit to me)

    Now would it be possible to mount such a distance measuring unit to a sort of rotating mount and have a computer interface?

    poor mystic,

    Before you mentioned LIDAR, I truthfully had no idea about it. Is it/does it operate along radar/sonar principles but using visible light instead of microwaves/ultrasound?
     
    Last edited: Jun 21, 2011
  13. davenn

    davenn Moderator

    13,654
    1,888
    Sep 5, 2009
    yes the standard ultrasonic transducer is 40kHz


    I couldnt help you with resolution sorry, havent done anything along those lines
    Have only used ultrasonics for remote control and distance measurements

    cheers
    Dave
     
  14. Solidus

    Solidus

    349
    4
    Jun 19, 2011
    Dave,

    do you have any idea what kind of range you get with 40kHz ultrasonics?
     
  15. davenn

    davenn Moderator

    13,654
    1,888
    Sep 5, 2009
    around the 30ft (10 metres) I dont know if they would stretch to 50 - 60 ft, maybe would depend on the enviroment and how much ambient noise there was

    Dave
     
  16. Solidus

    Solidus

    349
    4
    Jun 19, 2011
    If nothing else that doesn't seem half bad.

    Do they carry different frequency ultrasonics?
     
  17. davenn

    davenn Moderator

    13,654
    1,888
    Sep 5, 2009
    you would have to ask, I dont know
     
  18. poor mystic

    poor mystic

    1,066
    31
    Apr 8, 2011
    The easy-to-find ultrasonic send/receive pairs are 40kHz but the physiotherapeutic muscle massage machines such as used by top sports teams work in the megahertz, as do ultrasonic "acoustic radars" used by radiologists in hospitals.
    http://au.mouser.com/Search/Refine.aspx?Keyword=ultrasonic lists ultrsonic transducers from 25 - 300 kHz, I have not looked beyond the first results page.

    PS: as for range, that's a function of transmitted power and receiver sensitivity, both of which can be increased by using more pairs of transducers.
     
    Last edited: Jun 25, 2011
  19. poor mystic

    poor mystic

    1,066
    31
    Apr 8, 2011
    One thing about ultrasonics is that you have at least 2 and possibly several other methods to choose between for getting directivity.
    The 2 methods I know of are the parabolic dish and then half-wavelength array.
    Everybody believes he knows about parabolic dishes but few know much about arrays.
    Arrays can be made by setting a number of transmitters or receivers side-by-side in a straight line or on a plane with less than 1/2 a wavelength between adjacent units. According to simulations, arrays are much more directionally discriminating than parabolas.
    A mixture of the 2 techniques might be appropriate - a parabolic trough could lie horizontally and contain a linear array. Then you'd have poor vertical discrimination but good angular discrimination on the horizontal plane.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-