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Thread: Help with k-band antenna

  1. #21
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    That's not correct Hink. You're confusing what you think your seeing.
    Kfafnis isn't showing us all the pictures.

    So lets start with what you can expect to find in a radar gun.
    The Gunn Diode which kfafnis has shown us. I am not wondering why he pulled it out at all. So we either assume it is working or we test it and put it back together.
    And this time take the pictures that show the full detail of what you're working on. You have shown us pictures of two different things which look the same and they are not.
    Hence there is a lot more confusion here and nothing is getting fixed.

    So to clarify what Hink has mistakenly seen.
    There is only ever one gunn diode. There is never two. Not ever. The mistake here is another diode looks like a gunn diode.
    That other diode can be one of two things. It is sometimes a varactor diode which is used for either tuning or modulation.
    A gunn diode can be tuned and modulated without a varactor diode. There is no varactor in a radar gun because there is no point in having one.
    There is no need to electronically tune or modulate the carrier.

    But radar guns do have two diodes in the waveguide, sometimes three.
    The other diode is a mixer diode and if there is a third diode (another mixer) it is usually of reversed polarity to the first and set up as a quadrature detector.
    The radar is not capable of any distance measurement. The reason for this is the gunn diode is run CW mode. It would be not to be specifically run in a pulsed or modulated mode and the information of distance is kind of useless and overwhelming in this context.

    The quadrature detection of the mixer diodes does however provide direction information. Ether the target is a approaching or receding. A hand held radar gun will do one of two things. Display a negative speed "-" or it will ignore a receding target.

    The schottky mixer didoes don't act as any sort of overload protection. They are only mixer detectors. There may be a garden variety signal diode 1N914 which acts as a limiter the same as any other FM circuit but it does not offer any protection and it's not a schottky diode.

    ----

    Then there is the issue of using a radar gun in a moving environment. Of course it doesn't like it.
    There is a signal transmitted and there is a small rocky planet close by moving relative to the antenna. That's a pretty big target and return signal.
    All those trees and buildings, rocks and signs. That car by comparison is a small signal. The FM capture effect is going to lock the receive to the strongest signal.
    A hand held radar gun is not trying to compensate for any movement so naturally the strongest signal is the one of interest.

    A mobile radar is different and has a lot more signal processing. In general it's looking for the fastest return signal, the highest fundamental frequency.
    There's a couple of ways radar do the processing but one of the simplest is using a simple sigma delta demodulation and then processing the signal with a garden variety DSP chip.

    ----

    So where to from here .....
    Put the unit back together, take a picture of all of the waveguide components from all angles. Don't show the side of one piece and the front of another that looks the same and could be mistaken for the other.

    Commercial radar units also tend to be a little hard to modify. Even what appears to be a simple radar gun has a bit of error checking in it so even if you do a modification that would fool any hotwheels radar gun, a kustom is not going to be so easily fooled. This also makes using a radar jammer against them a bit ineffective.

    So I'm going to guess from the last description that there isn't anything wrong with the unit and kfafnis is a victim of the smarts of the gun.
    Changing the antenna is probably the fix. But hand held radar guns don't lend themselves to "better" antennas.
    You could improve upon the antenna with an external antenna, but if you're moving, a foxtel dish used as a better antenna is probably not your idea of a solution.

    A microwave lens is probably going to be your best and easiest first attempt at a patch.
    Yes I am an agent of Satan, but my duties are largely ceremonial.



  • #22
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    The impression I get from the OP is that he 'is' talking about an external antenna..... not a hand held unit, as he refers to stationary mode and moving mode.

    This suggests its a vehicle-mounted antenna and separate control/display unit.

    The OP can clarify. A model number may be helpful.

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    Thanks trash great description !!!

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    Quote Originally Posted by mtv View Post
    The impression I get from the OP is that he 'is' talking about an external antenna..... not a hand held unit,
    that's the problem with not having comprehensive pictures.... it's a guess.
    Kfafnis isn't the OP, but I had a look back over the pictures he did post to see if I recognise it as a hand held unit or mobile unit.

    ....when operating in moving mode
    does suggest that it is a mobile unit if he can switch modes.
    Yes I am an agent of Satan, but my duties are largely ceremonial.

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    This unit is a Kustom Signals Trooper, model number 064-0054, K band unit. It is a dash mounted radar that has a box that displays speeds and has the buttons on it. There is a remote antenna that has a 4 lead cable running to it.

    The FCC ID number of the antenna is CHY8BJK50. I have not been able to locate any wiring diagrams/ schematics for this equipment.
    I posted all pictures I took of the unit. I can take it apart again and do more thorough photographing if you would prefer.

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    Quote Originally Posted by hinekadon View Post
    Thanks trash great description !!!
    Don't mess with the Devil...

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