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  1. #1
    Experienced
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    Question STi problem with 34.7?

    I had a very poor experience today while driving to the mall. I ended up taking a jug handle. There was a LEO at the light going straight while I was coming around the jug, so I suspect he was in front of me the whole time.

    As I pulled around directly behind him at the red light, I say to myself "wow looks like he has his radar off", and about 2 seconds later, I get a 3-signal 34.7 alert. I followed him into the mall to confirm that he was the radar user. It was alerting the whole time I was behind him jumping between 4 and 9 signal strength counts, and disappeared as the he turned the other way. It was pretty clear he had his front antenna on as I was not getting full-blast strength as I was following him into the mall (which I would expect).

    The only problem here is the 3 second delay as I pulled up behind him. Now the only logical conclusion I can come up with here is that he just happened to flip it on after I pulled up behind him at the red light, but it doesn't seem practical as he was just going into the mall complex- why use I/O?

    While I understand this was off-axis, the STi practically would pick this up from ways away, and even a Cobra would most likely pick up the signal right as I got behind him. Any ideas on what the hell happened here?

  2. #2

    Default Re: STi problem with 34.7?

    Hmm...

    His radar gun could be malfunctioning. Thats really weird for the signal strength on your STi to jump around like that. Since the K and Ka band detection within your STi share nearly all of the same circuitry, put your STi in Highway mode and go check out some K band door openers. Park in the lot in front of the door openers (preferably at night when there aren't a bunch of cars driving around in the lot and people going in and out through the automatic doors) and check for steady K band signals. Then slowly turn your car away from the door openers and observe if the ramp-up smoothly and gradually ramps down. Then very slowly turn your car towards the door openers, pausing every 10 or 15 degrees of turn, and check for a steady alert what whatever signal strength is being detected.

    If your STi passes these tests without any weird sudden jumps in the ramp-up while your car is not moving, then I would say that the officer's Ka gun was flaky.

  3. #3
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    Default Re: STi problem with 34.7?

    Hmm ok, that makes sense. I still don't see why it would have a delay like that before picking up ANYTHING...

  4. #4
    Newcomer
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    Default Re: STi problem with 34.7?

    Maybe some1 at BEL can answer that question

  5. #5

    Default Re: STi problem with 34.7?

    Quote Originally Posted by Xen0n flash View Post
    Hmm ok, that makes sense. I still don't see why it would have a delay like that before picking up ANYTHING...
    I kind of misread your initial post. Yeah, I see now what you are talking about regarding the delay. I wonder if by chance there was a Cobra RD nearby which could have interfered with the STi, causing the STi to think that the Ka signal from the radar gun was instead coming from the Cobra? Two summers ago while on my way back from the northeast, I stopped at a Shoney's for dinner. I started getting stronger and stronger Ka band on my STi, and I figured that there was a cop headed my way. Hungry, I quickly parked my car, looked up, and saw a Cobra on the dash of a car parked 40 feet in front of my car. His older Cobra model was pointing straight at my car and my STi was displaying a Ka alert of a bit over 1/2 signal strength. I walked over to the other car and verified that the Cobra was indeed turned on and was the source of my Ka false alert.

  6. #6
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    Default Re: STi problem with 34.7?

    I doubt it was a Cobra. I was following him for a good 30 seconds. As soon as he turned the opposite way, the signal disappeared. But I'll give that test a try. If it fails, off to Bel it goes.
    Last edited by Xen0n flash; 03-21-2009 at 07:49 PM.

  7. #7
    Yoda of Radar
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    Default Re: STi problem with 34.7?

    Quote Originally Posted by Xen0n flash View Post
    I doubt it was a Cobra. I was following him for a good 30 seconds. As soon as he turned the opposite way, the signal disappeared. But I'll give that test a try. If it fails, off to Bel it goes.
    MEM-TEK is saying that a nearby Cobra might have suppressed the initial detection of the legit radar, not that you were detecting a Cobra the whole time.

  8. #8
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    Default Re: STi problem with 34.7?

    Quote Originally Posted by MEM-TEK View Post
    I wonder if by chance there was a Cobra RD nearby which could have interfered with the STi, causing the STi to think that the Ka signal from the radar gun was instead coming from the Cobra?

  9. #9

    Default Re: STi problem with 34.7?

    Hi XenOn,

    What I mean is this:

    If there is a nearby Cobra RD, then the STi's filtering algorithms will look not only for the Cobra's near X band LO frequency, but also will look for second and third harmonics of the Cobra's LO frequency. The third harmonic falls in the Ka band. Cobra RDs also black out rather strong LO signals which can be detected over 1000 feet away. Also keep in mind that the LO frequency not only is swept, but on many Cobra models the LO also "parks" for several milliseconds. Personally, I think that Cobra deliberately does this in order to try to generate false alerts in other radar detectors.

    So, what could have happened is this: There was a nearby Cobra RD. Your STi was "seeing" its swept primary LO frequency, and your STi was also "seeing" its swept 3rd Ka band harmonic at the same time that your STi was also detecting the police 34.7 Ka radar gun. This particular Cobra RD was also one of the models which momentarily parks it LO sweep. Now, also keep in mind that the officer's radar gun was forward facing, so its signal strength could have been fairly close to the signal strength of the 3rd LO harmonic from a nearby Cobra. The result then could be confusion in the STi's filtering algorithm as to whether or not to display any alert. On some signal sweeps the STi decides to display an alert while on others its filtering decides that it is a false alert. Then it seems possible to me that the alerting signal strength could jump all over the place.

    Anyway, this is just a theory. I may have to borrow a recent Cobra ESD model from my local Radio Shack and test this. It should make for some interesting videos.

  10. #10
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    Default Re: STi problem with 34.7?

    Update: I had another encounter of a POSSIBLE delay from the STi, this time with K band. My local LEO was ready to turn on my street from a stop sign, from the right. I passed him and then he turned on, right behind me. About 15 seconds later my STi went into full blast. Now while I'm pretty confident that he just happened to switch it on maybe to check my speed, my locals are known for C/O. Afterall, it stayed on the whole time after the alert.

    I also did a test at a speed sign. I turned the detector off, and then back on. It took a full 10 seconds before the alert came in. Is that the normal time it takes to alert when you switch it on before being alerted to radar already being thrown at you?

 

 

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