Re: Characteristics of traffic radar



Paul Hovnanian P.E. wrote:
I was thinking about radar speed guns the other day (No, I didn't get a
ticket). My understanding of these is that they produce an IF frequency
between the transmitted carrier and the Doppler shifted reflection in
the receiver diode. This is AC coupled(?) to an amplifier with a
passband in the audio region. Most traffic radar operates with Doppler
shifts in the audio band and, as a result, the signal may be monitored
through a speaker in addition to using a frequency counter.

What does the passband of the IF section look like in terms of its lower
and upper limits, dB/octave slopes, etc.? The initial AC coupling and
positive gain vs freq. would appear to create a bias toward selecting
the faster target over the larger one. However, at some point, there
must be a high frequency roll-off where the opposite is true.

Also, how would one characterize the rejection of amplitude modulation
in the receiver/mixer (if any)? The common technique for 'calibrating'
speed radar seems to be to use a tuning fork whose frequency corresponds
to some known speed Doppler shift. Unless radar guns are susceptible to
AM interference, it would seem that a tuning fork would be useless.
Unless one threw it, the average 'speed' of its tines would be zero
whereas the peak would depend on the amplitude of its vibration. Using a
tuning fork might verify the accuracy of the device's counter, but it
would also indicate that could register something other than a Doppler
shifted signal.



You can't be serious! Audio IF? Tuning forks? "positive gain"? "reflection"? "receiver diode"??? Hey!- where the hell is the cat whisker "crystal" rectifier? LOL- throw that TAB Books library of yours into the trash where it belongs. Your post is absolutely demented.

.

Relevant Pages

  • Characteristics of traffic radar
    ... I was thinking about radar speed guns the other day (No, ... Most traffic radar operates with Doppler ... it would seem that a tuning fork would be useless. ...
    (sci.electronics.design)
  • Re: Characteristics of traffic radar
    ... passband in the audio region. ... Most traffic radar operates with Doppler ... it would seem that a tuning fork would be useless. ...
    (sci.electronics.design)
  • [OT comment] Re: Doppler Ocsillation
    ... ornament" that consisted of a pair of counter-rotating wind-driven pinwheels in front of a reflecting screen. ... but any group that wants to use radar can hardly object to a reflector. ... Prosecutor produced 'expert' witness who demonstrated calibration by reflection from a tuning fork. ... Could you have set it up such that Doppler said you were either standing still or perhaps going backwards? ...
    (comp.dsp)
  • Re: Negative doppler shift
    ... shift its wavelength to LONGER wavelength instead of shorter. ... would really mess with police radar if your car was coated with it. ... cause a radar return but any measurement of doppler would indicate the ...
    (sci.military.naval)
  • Re: [OT comment] Re: Doppler Ocsillation
    ... ornament" that consisted of a pair of counter-rotating wind-driven pinwheels in front of a reflecting screen. ... but any group that wants to use radar can hardly object to a reflector. ... Defense claimed prosecutor had proved radar was unreliable as it was evident that guy holding tuning for was NOT going 60 MPH. ... Could you have set it up such that Doppler said you were either standing still or perhaps going backwards? ...
    (comp.dsp)
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