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Author Topic:   GPS Receiver Triggers Police RADAR DETECTOR Detector
jimh posted 08-02-2009 12:58 AM ET (US)   Profile for jimh   Send Email to jimh  
Recently while trailering my boat in Canada, I had a rather unusual encounter with an officer of the Ontario Provincial Police. I was southbound on Highway 400 about 50-miles north of Toronto, when an unmarked OPP patrol car came along side of my truck and then put on his flashers.

I pulled to the shoulder of the busy limited access highway. The rather young OPP officer came up to the truck, and he asked to see my license, registration, and insurance. I had all the paperwork and it was all in order. He only briefly glanced at it.

"Have I violated a traffic law," I asked.

"The reason I pulled you over," the OPP officer replied, "was because you set off my RADAR DETECTOR detector when you went by me. Do you have a RADAR DETECTOR?"

As a matter of fact, I did not have RADAR DETECTOR, which, from the OPP's strong interest in I concluded must be illegal to have in a car in Ontario. The officer asked us to open our glove box and center console storage. We showed him a collection of cellular telephones, charger cords, and other odds and ends.

"I do have some radios on the boat," I told him. He didn't seem impressed. He was certain we had a RADAR DETECTOR. Apparently the indication he got on his equipment had been very clear. However, failing to find any evidence of one, he let us go. We got back on the road and headed off toward America.

As we got back up to speed on the highway, I began to think about the situation. What could have set off his detector? It then occurred to me that my GPS receiver antenna was probably the culprit.

I have an older GPS receiver which has an actual antenna connected to the head unit. More modern devices have the whole receiver built into the antenna casing, but mine is several generations old and has an antenna with probably only a down-convertor. It is located on the starboard stern quarter of the boat. The OPP vehicle was parked on the side of the road. I was driving in the right lane. When I passed him the GPS antenna was only a few feet away from his vehicle and his detector.

GPS uses the L-band for the carrier signal. The police RADAR DETECTOR detector probably picked up the L-band antenna for the GPS.

I wonder if this has ever happened to anyone else trailering a boat with a GPS receiver. Let me hear from you it you were ever stopped.

fishgutz posted 08-02-2009 11:30 AM ET (US)     Profile for fishgutz  Send Email to fishgutz     
Jim, something doesn't make sense. Your GPS is a receiver. It doesn't transmit any signal, does it? What could he be picking up? I know all electrical devices give off some radio waves albeit small and rarely detectable. Got to research this more. Seem odd.
fishgutz posted 08-02-2009 11:39 AM ET (US)     Profile for fishgutz  Send Email to fishgutz     
Found this: Which explains how the detector detector works and what it detects. So I understand how a detector does in fact radiate some electrical field. But a GPS? I think his detector detector was his eyeballs sighting your GPS on your dash.

So I admit you are a bit smarter than me in this field but I really didn't think a GPS transmitted any signal or any normally detectable signal.

I use an old Garmin GPSMAP76 on my dash. On occasion I have used a magnetic mount external antenna ( just a little background).

Very interesting occurrence. Quite an inconvenience.

fishgutz posted 08-02-2009 03:38 PM ET (US)     Profile for fishgutz  Send Email to fishgutz     
Hold the phone. Jim, do you by any chance have "back-up sensors" on your tow vehicle? They work by radar. Wait, if you're towing you usually have to turn those off. Darn, thought I was on to something.
deepwater posted 08-02-2009 03:42 PM ET (US)     Profile for deepwater  Send Email to deepwater     
I found it just as simple to leave early and ease up on the gas pedal a smidgen arrive a little early and find a coffee shop and relax
jimh posted 08-02-2009 09:33 PM ET (US)     Profile for jimh  Send Email to jimh     
FISHGUTZ--The device which a RADAR DETECTOR detector tries to detect is a RADAR DETECTOR. A RADAR DETECTOR is a microwave receiver, precisely the same as a GPS receiver is a microwave receiver. A RADAR DETECTOR is not a transmitter, nor is a GPS receiver a transmitter.

The Wikipedia article (referenced and linked above) mentions the principal of operation of the RADAR DETECTOR detector is to listen for local oscillator leakage from the RADAR DETECTOR. This means the device would have to be powered on. I am certain that my GPS was not powered on when the OPP officer pulled me over. I know this because at the next stop we made, I jumped up into the boat to check the GPS receiver; it was OFF. Thus if the OPP was using a detector that listened for local oscillator leakage, he would not have found anything emitting from my GPS.

I don't know how sophisticated the OPP equipment might be. The only microwave frequency device on my boat or truck is my GPS. The OPP officer seemed extremely certain that my vehicle had set off his detector. Even though he could not find anything, he gave me a look that said he thought I was guilty and was hiding something. He was really a dog on a hunt.

I was speculating that perhaps there is some sort of detector that is active, and it emits some microwave energy. It them looks for any enhanced backscatter of the microwave, as might occur from a resonance in an antenna.

The simplest explanation is that someone else drove by in another lane with a RADAR DETECTOR and the OPP officer just made a mistake. I would be curious, however, to know if anyone else has ever been stopped when towing a boat with a GPS and suspected of having a RADAR DETECTOR.

DEEPWATER--I don't need a RADAR DETECTOR, as I don't drive fast, either. But I am not interested in collecting anecdotes about the driving habits of people. I am interested in a technical discussion of how a GPS receiver might be confused for a RADAR DETECTOR.

jimh posted 08-02-2009 09:39 PM ET (US)     Profile for jimh  Send Email to jimh     
To clarify, we don't have a GPS in the car. The GPS was in the boat.

I can't imagine that the typical RADAR DETECTOR detector would be fooled by a GPS because so many vehicles have a GPS now. Half the cars on the road would be setting the thing off with false alarms.

But most of these modern GPS receivers are now very small and compact. They are built completely into a small chip: antenna, receiver, and demodulator all in one little package. My old GPS is archaic by modern standards. It has a separate passive antenna with coaxial cable connecting to the actual receiver. That might behave differently.

fishgutz posted 08-02-2009 10:24 PM ET (US)     Profile for fishgutz  Send Email to fishgutz     
I guess it's back to my statement; "I think his detector detector was his eyeballs sighting your GPS on your dash."
roloaddict posted 08-03-2009 12:54 AM ET (US)     Profile for roloaddict  Send Email to roloaddict     
Do you have an amplified TV antenna on you tow vehicle or boat?
roloaddict posted 08-03-2009 01:01 AM ET (US)     Profile for roloaddict  Send Email to roloaddict     
Maybe your antenna power circuit had enough cap to power the antenna's amplifier. Perhaps your antenna amp has a harmonic that is in what ever band he is on.
dfmcintyre posted 08-03-2009 05:37 AM ET (US)     Profile for dfmcintyre  Send Email to dfmcintyre     
Fishgutz -

Re-read Jim's earlier post....he does not have a GPS unit in the car.



striper swiper posted 08-03-2009 07:22 AM ET (US)     Profile for striper swiper    
Radar detector detector? I think that's an expensive piece of police equipment used for an excuse to stop motorists, and I think he should be using his radar detector to catch speeders rather than the infrequent radar detector carrying motorist who isn't speeding.Also , motorists with radar detectors usually drive past the posted limit , so he could catch to birds with one stone,"eh?"

I think he may have been blowing smoke up you know where.

fishgutz posted 08-03-2009 09:00 AM ET (US)     Profile for fishgutz  Send Email to fishgutz     
Duh my bad, I'm betting it was just a mistake. Someone else set it off.
David Pendleton posted 08-03-2009 12:35 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
Radar detectors are illegal in Canada.

Buckda posted 08-03-2009 12:37 PM ET (US)     Profile for Buckda  Send Email to Buckda     
This was interesting - I witnessed the whole thing. Jim was in the lead and we were entering the freeway via an access road when we passed the "subdued markings" vehicle. He pulled out behind my rig and followed us onto the on ramp.

Once on the highway and up to speed (100 KPH - or around 61 MPH), he pulled out into the middle lane and slowly passed me. When he was just beyond my truck, he turned on his flashers and squeezed between us and pulled JimH over.

Incidentally, I DO have a radar detector in the console of my vehicle, though I rarely ever use it due to false alarms. I also have reverse radar on my truck bumper, which was not turned off because I had not used the reverse gear since the vehicle was restarted after our last stop.

Perhaps I was the culprit - and he really meant to pull me over?

If so, I was fortunate, as the unused radar detector in my console would have earned me a ticket.

My vehicle is also equipped with a built in satellite navigation system and satellite radio. However, both GPS units I have on the boat were removed and completely disconnected.

On a final note, JimH and I were conversing on two Motorola Family Band handheld two-way radios at the time.

So there was a lot of radio wave activity in the area, not to mention the other vehicles on the road!

I do agree that he must have "picked us up" on the access road as we passed him and he followed us onto the limited access freeway that leads to Toronto.

David Pendleton posted 08-03-2009 02:32 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
So do you think Canadian LE is pulling over everyone with active back up sensors?

That'd be interesting.

Buckda posted 08-03-2009 03:15 PM ET (US)     Profile for Buckda  Send Email to Buckda     
I'm not sure that the reverse sensors are activated until you actually engage the reverse gear. Mine indicate proximity by a series of tones in the passenger compartment, and those tones are not engaged until you engage the transmission into reverse gear.

Since JimH reports that his GPS was actually OFF, I'm wondering if it isn't a case of mistaken identity? Something doesn't add up. The cruiser was a new Dodge Charger - so it's electronics, unless scavenged from earlier duty in another cruiser, were likely to be new or current.

striper swiper posted 08-03-2009 05:38 PM ET (US)     Profile for striper swiper    
David Pendleton posted 08-03-2009 11:10 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
My backup sensor is a ball-mount.
deepwater posted 08-04-2009 06:53 PM ET (US)     Profile for deepwater  Send Email to deepwater     
Sorry jimh if i stepped on your toe
bluewaterpirate posted 08-04-2009 10:23 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
Navy term used to diagnose an unexplainable event. PFM ........ Pure Freaking Magic.


jimh posted 08-05-2009 08:32 AM ET (US)     Profile for jimh  Send Email to jimh     
In retrospect, the encounter with the OPP was a bit odd. The notion that while pulling a rather large boat and trailer I would be exceeding the speed limit is curious. As I told the OPP officer, I'm the slowest vehicle on the road. I drive in the right lane and usually travel between 55- and 60-MPH. I was pushing it to maintain 61-MPH or 98-KPH to keep up with traffic on the highway.

My old truck is from the era before GM went to the VORTEX 5.7L engine. I only have 210-HP. Although rated for 7,000-lbs of towing, believe me, we are right at that limit with our boat, gear, and two of us in the truck. I have often driven long stretches, say 300-miles, and not passed a single other vehicle on the road. My vehicle was probably the least likely to need a RADAR DETECTOR of all those on the highway that day.

Ironically, at least in the United States, I believe it is legal for me to possess a microwave receiver in my vehicle by virtue of having an Amateur Radio license. The Amateur Radio Service is allocated frequencies in the same microwave regions as used for law enforcement speed RADAR, and it is technically legitimate for a radio amateur to have a mobile station with such a receiver. This might be a point of law that you'd have to sort out in a court room, but as far as I know, it would not be illegal for me (again, in the U.S.A.) to have a microwave receiver in the truck.

As for whether or not RADAR DETECTORs should be permitted in Ontario, I am afraid I don't have much standing. Since I am not a citizen of Canada nor a resident of Ontario, I don't think I would have much voice in a debate on the topic. When traveling in foreign countries, I generally figure that their rules apply and I try to abide by them.

One final comment: the sun visors in our truck have elastic straps on them which can be used to retain items to the visor. The original owner of the truck must have had something large stuffed under these elastic straps, because they have always been stretched out and have lost their elasticity. I know that many times the sun visor is used to hold a RADAR DETECTOR. I think when the OPP officer came up to the car and saw those stretched sun visor elastic straps he must have figured he was swooping in on a hot crime scene and we had just hurriedly concealed the contraband previously housed there. Also, when we initially passed by him, these visors would have been backlit by the sun, and he might have looked up and seen what appeared to be something on the sun visor.

In the end, it was brief five minute delay in our trip home, which otherwise was uneventful. We even timed our border crossing superbly, and we drove from Sarnia to Port Huron across the Blue Water Bridge without a moment's delay.

an86carrera posted 08-05-2009 08:54 AM ET (US)     Profile for an86carrera  Send Email to an86carrera     
There are states (Ct and Va) that specifically outlaw the use of radar detectors. I wonder if you being a amature radio operator overides that law?

But, then again we all have the right to recieved transmitted signals except in a car where many rights are taken away. An example would be police scanners are OK at home but not in a vehicle.


jimh posted 08-05-2009 08:07 PM ET (US)     Profile for jimh  Send Email to jimh     
Since I hold the both the highest class FCC commercial and amateur radio licenses, it is hard to imagine a situation in which it would be illegal for me to possess a radio receiver, but, as I mentioned before, that is a card which you might only be able to play in front of a judge or magistrate, and even then a sympathetic judge or magistrate. And in this case I had no proof of either license with me in the truck.

Again, not much came of this stop except a brief delay in our travel. It appears that there probably was not any underlying technical reason why my GPS antenna could have caused a law enforcement RADAR DETECTOR detector to indicate a false positive. I guess we can chalk this one up to over an zealous young patrol officer making a mistake in identifying the source of the alarm signal.

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