# Thread: J Function Operating Principles?

1. ## J Function Operating Principles?

Hi,

Understanding the operating principles governing V1's J feature might better enable us to understand why it J's out real threats so frequently, and consequentially help us to recognize instances in which V1 J's out a threat when it shouldn't.

Does anyone know what the operating principles are? That is, what set of occurrences causes V1 to J out a Ka alert?

I thought of the following possibility. Let me know how plausible you think it is: V1 alerts in response to a signal on the Ka band quickly (so that it doesn't miss a quick Ka POP burst), before it has time to sweep for a local oscillator fundamental frequency (11 or so GHz) or second harmonic (23 or so GHz) which corresponds to the signal on the Ka band (35 or so GHz). After it has swept for and found such a fundamental or second harmonic, V1 realizes that what it originally thought was a Ka alert was merely the third harmonic (at 35 or so GHz) of this corresponding fundamental (at 11 or so GHz) and that, as such, what it previously thought was a legitimate threat turned out not to be. Thus, it retracts its original alert with the 'J'.

If this were true, we could see how V1 would J out real Ka threats. If another detector, say, were in close proximity to V1 when a genuine Ka threat was in the area, V1 could mistake the local oscillator fundamental or second harmonic being emitted from this detector as one which corresponds to the real Ka alert. As such, V1 would think that the real Ka alert was merely the third harmonic of this detector's local oscillator fundamental or second harmonic and, consequentially, J out the alert.

Is there any merit to this theory?

ben

Welcome to the forum, nice name.

3. ## Re: J Function Operating Principles?

Originally Posted by njasshole
If this were true, we could see how V1 would J out real Ka threats. If another detector, say, were in close proximity to V1 when a genuine Ka threat was in the area, V1 could mistake the local oscillator fundamental or second harmonic being emitted from this detector as one which corresponds to the real Ka alert. As such, V1 would think that the real Ka alert was merely the third harmonic of this detector's local oscillator fundamental or second harmonic and, consequentially, J out the alert.

Is there any merit to this theory?

ben
welcome.

i saw that exact same scenario happen. we were in a parking lot, picking up ka from a police dept. across the street, when someone pulled in (between us and the ka source) and as they pulled up to us, the V1 "J"ed out and stayed quiet. the car had an 8500/X50 in it on the windshield.

after other discussions on this i'm pretty convinced that is exactly what is happening.

that would also explain why some people have this problem and some don't, it's one of those "right place at right time" situations.

unfortunately it is possible that could turn into a "right place wrong time" situation.

4. Yes, that is basically how the feature works:

-If a 2/3 freq signal is detected a number of seconds before or within a few sweeps of when the Ka signal is detected, then the alert is suppressed completely. This works OK most of the time, since the 2/3 freq signal will normally be stronger than the Ka freq produced.

-The "J" feature comes into play in the situations where a 2/3 freq is not immediately detectable, due to bandpass filtering in the interfering detector etc that suppresses the second harmonic. The V1 first detects the Ka and reports the alert, since it might be valid police radar. If a 2/3 freq is detected once the alert is alredy in progress, the alert terminates with the "J".

Search around on here and you'll find this heavily discussed, since many have reported potential problems with the "J" feature.

Jim

5. I don't have the vast knowlegde that Prof Jim has, but maybe to fix/alleviate the "J" alert cancelling out real threats is:

If a valid Ka signal is found, and a POS detector is found in the vicinity as well, quickly compare the harmonics to see how close it is to the actual threat.

Say if LO was 11.211GHz.

1st Harmonic = 11.211 GHz
2nd Harmonic = 22.422 GHz
3rd Harmonic = 33.633 GHz
Real Ka = 33.810 GHz

If another source is found outside a .200MHz window from the radar threat supress the harmonic or show an additional 'bogey'. It would require I guess more precisely (float point precision?) calculations as where the V1 would analyze the harmonics more precisely to determine if its a harmonic or not. Like I said its a theory most likely it wouldn't work but it could who knows.

6. Not that I'm paranoid..but I am :P

.. A tech at V1 said it wouldn't happen.. but do you think a crafty Radar manufacturer or LEO might devise a device(or incorporate it into their gun that would essentially "J"unk out the V1, and then hide behind it?

Originally Posted by jimbonzzz
Yes, that is basically how the feature works:

-If a 2/3 freq signal is detected a number of seconds before or within a few sweeps of when the Ka signal is detected, then the alert is suppressed completely. This works OK most of the time, since the 2/3 freq signal will normally be stronger than the Ka freq produced.

-The "J" feature comes into play in the situations where a 2/3 freq is not immediately detectable, due to bandpass filtering in the interfering detector etc that suppresses the second harmonic. The V1 first detects the Ka and reports the alert, since it might be valid police radar. If a 2/3 freq is detected once the alert is alredy in progress, the alert terminates with the "J".

Search around on here and you'll find this heavily discussed, since many have reported potential problems with the "J" feature.

Jim

7. doubtful... if the radar manufacturer is going to make the radar better he will do what mph has done and develop a better way of making radar guns avoid detection by all radar detectors!

it would be like making a spectre to detect the bel sti only, they wouldnt do it...

with the j function they are unsure where the problem is, it would be the principle of junking out signals, or it could be a glitch with how it does it...

if you could see radio signals in the air there are far too much of them, far too much unnessary radio waves..... its like listening to destorsion through the radio... or machine gun sounds from your scanner..

its a wonder they all dont interfere with each other!

i think mike should have put rmr of his list of polluting detectors!

8. Originally Posted by RensoreK
I don't have the vast knowlegde that Prof Jim has, but maybe to fix/alleviate the "J" alert cancelling out real threats is:

If a valid Ka signal is found, and a POS detector is found in the vicinity as well, quickly compare the harmonics to see how close it is to the actual threat.

Say if LO was 11.211GHz.

1st Harmonic = 11.211 GHz
2nd Harmonic = 22.422 GHz
3rd Harmonic = 33.633 GHz
Real Ka = 33.810 GHz

If another source is found outside a .200MHz window from the radar threat supress the harmonic or show an additional 'bogey'. It would require I guess more precisely (float point precision?) calculations as where the V1 would analyze the harmonics more precisely to determine if its a harmonic or not. Like I said its a theory most likely it wouldn't work but it could who knows.
Yes, it's a good idea, and at one point, I actually thought that the V1 used a similar "selective" method of Ka filtering where only a Ka alert was suppressed if it corresponded to the harmonic within a certain bandpass. I'm pretty sure this method has at least been used at some point in the past.

And, I thought the Belscorts suppressed Ka alerts throughout the band if they detected interference at ~11 and/or ~22 GHz. (Anyone remember reading about the "Ka Krisis" on a couple of the Aus. websites? That's what this was.)

But with the reported problems with the "J" feature, now I'm not sure. It almost appears as though V1 suppresses Ka alerts in the entire band if ~22 GHz interference is detected (I don't think V1 examines ~11 GHz).

But then again, we don't know the root cause of the reported problems with the "J" feature. But, there's a couple of main theories:

-At close range, strong signals produce image frequencies around ~22 GHz that V1 sees, and J's out the alert.

In this case, maybe any ~22 GHz interference causes V1 to J out the alert. But on the other hand, maybe the strong signal for some reason produces images in a bandpass that corresponds with the Ka harmonic.

-Other detectors around at the same time produce interference around 22 GHz, and V1 J's out the alert (like njasshole spoke of above)

One would think that if the V1 was using "selective" Ka filtering, then this scenario wouldn't happen, as a Ka frequency produced by harmonic from a junk detector would likely be significantly different than the real Ka radar detected.

But I was thinking: some detectors will "park" when they detect a signal (which is one reason why you shouldn't run two together). Who's to say that there aren't detectors out on the road that, under normal operation, don't cause problems, but when receiving a real Ka signal "park" their oscillator in such a manner that causes a harmonic to be produced that actually falls within a bandpass that could be used with "selective" filtering which would cause the V1 to "J" the alert?

Also, I am pretty sure that the V1 contains some algorithms to filter Ka false alerts for some spefiic models of other detectors. There might be something going on here that we haven't even anticipated...

Right now, I guess I would have to lean towards the "other detector around causing V1 to J real alerts" theory, just because VR has claimed that the "J" problem is fixed.

But junk detector or not, I could understand why people would be concerned with it J'ing out real radar sources, no matter what the reason.

Jim

9. But whats the explaination when there is no other cars in the area as people have reported... in another just recent thread (Email from VR about "ghosting"), they mentioned that a strong signal can possible overload/confuse the RD, any RD for that matter, thus getting this situation of "ghosting", and if getting this "ghosting", the V1 may interpret this as a false harmonic and J out the signal. Sounds plausable to me.

10. RensoreK, I'm liking your thinking here. As I'm not an expert either I'm not sure how practical your fix is, but you're definitely headed in the right direction:

Essentially, V1 needs to be able to differentiate between a real Ka threat and a third LO harmonic to be able to continue to alert when a signal in the Ka band is a real threat and J out an alert when the signal is merely a third harmonic.

As it stands, it seems that the J feature is fundamentally flawed because V1 is as of yet unable to do this. A second harmonic in V1's vicinity which V1 associates with a (cotemporary) signal in the Ka band could cause V1 to J out a real Ka threat because V1 doesn't yet have the ability to determine whether this signal in the Ka band is a real threat or a harmless third harmonic.

All that's required for a second harmonic to be in V1's vicinity is, for example, another detector in sufficient proximity to V1, so V1 could understandably J out a legitimate threat at any time. This is, it seems, too dangerous a possibility and must be corrected.

ben

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