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Thread: what is "POP"

  1. #1
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    Default what is "POP"

    I hear a lot of talk about POP. What is it. Can't find an explanation in search.. :?:

  2. #2
    Speed Demon
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    Default Re: what is "POP"

    Quote Originally Posted by nakkas
    I hear a lot of talk about POP. What is it. Can't find an explanation in search.. :?:
    Pop is a radar that gets speeds at lightning fast rates at short distances.

  3. #3
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    POP is a feature in some of the newer MPH Industries radar guns. When in POP mode, the gun generates a very short pulse of radar (67 ms or 16 ms depending on the gun). This pulse is difficult to detect by radar detectors, though the latest versions of the Big 3 and a few others have POP detection now.

    POP is only supposed to be used to get an estimated speed. The officer is supposed to switch to normal (instant-on) mode to lock in a speed before issuing a ticket. This is because POP doesn't give doppler tracking history, and it can also produce speed readings that aren't accurate. Of course, some cops still issue tickets solely based on POP readings.
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  4. #4
    Good Citizen
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    Default

    POP is what us midwesterners call SODA. So if you are not in the midwest, make sure your detector has SODA in it.

  5. #5
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    see the valentine website. www.valentine1.com

    this is what mike valentine says about pop....

    Local ticket writers have been bragging about their new radar; They say it nails detector users without warning.

    Yes, their MPH Industries model BEE™ III, with its POP™ mode, gave them an advantage for a while. But now V1 has full-time POP Protection on two bands. Yet a problem remains. When operated in its POP mode, those radars also produce erroneous speed readings every time.

    Moreover, we believe MPH Industries knows this feature is faulty. Why else would it advise, in the accompanying Operation and Service Manual, as follows:

    “A note of caution: Information derived during the POP burst is non-evidential… Citations should not be issued based solely on information derived from the POP burst.”

    In actual testing of a BEE III in our laboratory, we quickly learned why MPH Industries is covering itself in the fine print. The POP mode is fundamentally flawed. It consists of a lightning-quick radar burst, over and done with before a radar detector can pick up the signal. We consistently measured the POP duration at 67 milliseconds (that’s 0.067 second).

    Unfortunately for accuracy, that burst is over the speed limit for the BEE III’s own internal components.

    All traffic radar units rely on a Gunn oscillator to produce a stable, reference frequency for the microwave beam. This reference frequency must be held constant throughout the entire reading. Here’s how radar works: A microwave beam at the reference frequency is transmitted toward the target. The radar unit then compares the reference beam to a reflection of that same beam after it has bounced off a moving vehicle and returns to the radar unit. The difference between the reference frequency and the reflected frequency—known as the Doppler shift—gives the speed of the moving vehicle.

    No Gunn oscillator we’ve ever tested can go from “off” to “on” and back “off” again in 67 milliseconds while simultaneously holding its frequency. This is basic physics. To be “on,” electrical current must flow through the oscillator. As the current begins flowing, it inevitably heats the component. While the device’s temperature is changing, so is its frequency. After a second or so under power, the device will reach its constant operating temperature and it will hold steady at its design frequency.

    However, during the short cold start from ambient temperature to operating temperature, the device is literally out of control. Component makers don’t even bother to quantify the frequency change—called a start-up chirp in electronic jargon—because Gunn oscillators are designed as steady-state devices; they’re not intended for cold-start use.

    What does this start-up chirp mean for ticket accuracy? The answer is really unknowable, because it’s influenced by a number of variables. For example, how far away is the target vehicle? The longer the distance, the greater the error. What’s the target speed? The slower it is, the larger the percent error. Which way is the target moving? The error adds to the speed of vehicles approaching the radar, and subtracts from vehicles heading away.

    Clearly, MPH Industries has stepped into foul territory with the POP mode. In its zeal to defeat detector users, it has created a radar unit operating outside the accepted principles of engineering. Then it has tried to paper over its own technical recklessness by advising police operators, sotto voce in an obscure section of the manual, that they can’t use the BEE III’s key selling feature for its plainly intended purpose.

    Question number one: Given the widespread ignoring of manuals, will anyone even read that warning?

    Question number two: If they read it, will they heed it?

    MPH Industries, in its quest for corporate profits, is playing an unconscionable game with its law-enforcement customers. Traffic radar is bought for one reason; it’s a ticket machine. Promising a feature, then telling the police after the sale not to use that feature for writing tickets, is pure bait-and-switch. Moreover, it dangles a temptation, a moral hazard, that threatens to corrupt enforcement. MPH Industries must be compelled to recall all BEE IIIs at once and disable the fundamentally faulty POP mode.

    and how the oscillator works, technical info!

    The POPtm burst works by cold starting the radar’s Gunn oscillator, and its 67 ms duration is shorter than the component’s warm-up time, so the entire POP takes place in a period of frequency transition. The chirp rate is a measure of frequency change per unit time during this POP. We tested the one MPH BEE IIItm available to us and determined the chirp rate of its Gunn oscillator.

    What would be the chirp rate of other BEE IIIs? As a way to create an envelope of possibilities, we tested quite a few Gunn oscillators in our own stock (we buy them for test gear we design for use in our laboratory) and we confirmed that our BEE III sample falls within the range of commercially-produced components available to any manufacturer. Interestingly, we had never tested this parameter before, because it is irrelevant for the steady-state applications intended for these components.

    The best rate (lowest) in our test is -0.0198 Hz/nsec; the worst is -1.069 Hz/nsec.

    During a POP burst, this frequency change adds (or subtracts, depending upon direction of vehicle travel) to the Doppler shift, causing an error in the speed reading.

    The Doppler shift used by the BEE III operating on a Ka band at 33.800 GHz to calculate speed of the target vehicle is based on the following formula: 1 mph = 100.803 Hz.

    The Doppler shift error rate due to chirp is determined by the following formula: chirp rate in Hz/nsec multiplied by propagation delay of light (inverse of speed) in nsec/ft. The best (lowest) rate of Doppler shift error in our sample is -0.02015 Hz/ft of wave travel; the worst is -1.087 Hz/ft.

    The actual Doppler shift error increases with distance the wave must travel (out to the target and back) as follows: Doppler shift error rate multiplied by total distance.

    Distance matters here because radar works by comparing the frequency of a transmitted beam to the frequency of a returning echo of that beam. Since the echo is being returned from a moving target, the echo frequency is either higher (for approaching targets) or lower (for departing targets) by the amount of the Doppler shift. If the frequency being transmitted changes before the echo returns, then the returning frequency will be compared to a fictitious reference. Longer distances increase the time before return, allowing an out-of-control reference frequency to change more.

    For the best Gunn oscillator we’ve tested, the error at 1/2-mile range calculates as follows: 0.02015 Hz/ft multiplied by 2640 ft multiplied by 2 (out and back) divided by 100.803 Hz/mph = 1.1 mph.

    For the worst, 1.087 Hz/ft multiplied by 2640 ft multiplied by 2 (out and back) divided by 100.803 Hz/mph = 56.9 mph.

    The following table shows the radar error for best- and worst-case Gunn oscillators we’ve tested.

    ------------------ Radar Error ---------


    Range.............Best-case..............Worst-case


    500 ft...............0.2mph................10.8mph
    1/4 mile...........0.5mph.................28.7mph
    1/2 mile...........1.1mph.................56.9mph
    3/4 mile...........1.6mph.................85.4mph
    1 mile..............2.1mph.................113.8mph
    1 1/2 mile........3.2mph.................170.8mph


    bloody funny how mph industries calls this accurate!

  6. #6
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    Quote Originally Posted by goofy173
    POP is what us midwesterners call SODA. So if you are not in the midwest, make sure your detector has SODA in it.
    Good point.

  7. #7
    Longsnowsm
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    You might hear the term "sody pop". It's the same stuff...

  8. #8
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    of course....

 

 

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