A secondary -but planned!- use for the speed-detecting radar signal?

Wouldn't a simpler explaination be that its an unlicensed spectrum which is well suited to use for radar?

Door sensors use radar to detect people, I don't know about ambulances but I can think of a couple of reasons they might want to be able to detect obsticals, at the airport near here we have little cameras setup to record number plates as cars are leaving, your toll booths could have a similar system in place connected to a motion sensor.

I can't see the benefit of installing hundreds of thousands of dollars worth of radar gear just for the benefit of the minority who have radar detectors. Especially when the people with the radar detectors obviously haven't been told about it so their first instinct is to look for cameras drawing attention away from ambulances, toll booths, etc.

-- Michael Heydon

On Mon, 26 Mar 2007 15:21:17 -0700, Ramon F Herrera wrote: ...

...

That's done with a strobe light, that flashes at a certain rate. Radar has nothing to do with it.

Cheers! Rich

I should have explained (I thought it was obvious) that when a nearby ambulance is in emergency mode, my radar detector goes crazy. As the ambulance goes away, the beeping of my RD slows down.

I find rather doubtful that my RD has an optical strobe light detector. When it boots up, it clearly displays: X-Band, K-Band and Laser. All 3 are electromagnetic radiations, but they are very far from the strobe used by ambulances and the infrared used by street light preempting devices.

A reader in another newsgroup confirmed my suspicion: the emergency vehicles indeed carry a low level radar transmitter *only* whose specific purpose is to turn on your RD, and cannot measure (or care) about your speed. It is the high tech way of saying "out of my way!". That device is cheap enough, specially when balanced against human lives and property they save, Michael Heydon.

-Ramon

Now I understand your point. Are you saying that what is detected is the low frequency (as it can be counted by a human being) rate, as opposed to a certain modulated frequency, like the ones used to distinguish a VCR remote control from a TV remote control?

What about day vs. night, obstacles, fog, etc?

If I can afford a *precise* infrared remote control made by Sony ($9.95 at Radio Shack) the police and fire departments in a life critical jobs, certainly can.

-Ramon

Aha! My suspicions were correct. The strobe-light detector seemed too crude, susceptible to errors, easy to counterfeit. Plus, you want the street-light preempting functionality to be independent of the strobe, visible light.

I got this from another NG (sometimes it pays to cross post):

-Ramon

----------------

Well, traffic engineers know quite a bit about radar, its attendant transportation and non-transportation uses, and emergency vehicle pre-emption (EVP).

Modern EVP systems use an encrypted signal sent via a modulated 14.035 Hz wave. If it seems low frequency, it is. Most systems send the signal out whenever the front strobe lights of the vehicle are flashing (and it is obviously invisible, with visible light being several orders of magnitude higher in frequency).

You'll occasionally see peace officers detaining a motorist, the whole time leaving their forward strobes activated and tying up traffic in all directions but their own (which is usually already tied up behind them). I had a conversation with the Cook County Sheriff's Department one morning a few years ago after they repeatedly destroyed the operation of a busy suburban intersection over several days. They would pull over speeding motorists and direct them onto a side street for an entertainment venue that had zero traffic in the AM peak. The motorist and the sheriffs patrol vehicle would end up facing back out. Because of the EVP call, the traffic signal was held in green for the EVP max-out (about two minutes), then recalled immediately after returning to serve the other movements. This left the main arterials (the cross road and the oncoming arterial) with about six seconds of green per cycle - and no arrows for the left turns, either, since the detector loops "tuned out" after a few of those incidents and were not vacated to "reset" until after the AM peak had diminished.

Obviously, the only real "fix" for a problem like this, from a traffic signal control standpoint, is to not serve an incoming EVP call until the previous call is terminated, if the call is from the same unit.

This requires that the EVP module recognize the difference between a fire truck and an ambulance, so that vehicles in a procession but separated are not denied calls on the basis of the passage of a previous vehicle. There are pitfalls to this practice (all units must have unique ID's), but it's probably easier than asking the cops to turn off their forward strobes (although some agencies are very good about strobe light and traffic advisor management, most are ignorant of good practices).

-- Scott O. Kuznicki, P.E. Civil (Traffic) Engineer Dedicated Highway Enthusiast Driving Enthusiast: '03 525i 5-speed '90 Ninja 250R (cheap fun!)

On Mar 27, 10:21 am, "Ramon F Herrera" wrote: The mall door are perhaps a

RF used to detect tags on goods.

X band radar is on a "license free" allocation near 10.5 ghz. Door openers, microwave car detectors, are in a "license free" allocation at 10.5 ghz. A while back it was decided to add a signaling protocol to some radar detectors for emergencies and certain roadway warning signs at you guessed it, 10.5 ghz.

Does that answer your observation questions?

Steve Roberts

"GPG" said in rec.autos.driving:

Um, no.

Automatic door openers triggering radar detectors predate RFID by many decades.

RFID tags are typically in the 1-2GHz range... but there are some as low as 130KHz ;-)

...Jim Thompson

That could be, as an attention-getting device - after all, when your radar detector sounds, you wake up and get back to the task of driving the car responsibly, right?

So I can see that it's marginally feasible, but whatever radar jammer they're running doesn't have anything to do with changing the signals.

Thanks, Rich

...

It's a strobe with a flash rate of 14.035 flashes per second.

And if they catch you using one, they'll throw you in the clink.

Good Luck! Rich

Thanks for your answers, Steve. Let me see if I understood you correctly. You say that a signaling protocol was added with the specific use of sending a "this is an emergency, get out of the way" signal to properly equipped RDs. If that's the case, shouldn't the display show something like "emergency vehicle coming"? I really have bumped into many ambulances in emergency mode, but IIRC the display and beeping sound is the same than for a regular police patrol car.

-Ramon

"SWS" aka safety warning system, 64 canned messages transmittted on a x band or Ku band carrier,

see:

I doubt it will catch on outside of california or other real dense traffic areas, too limited in the scope of messages, and number of cars that can receive it.

Steve

Google a little, Google a lot. Type "radar detector" and read the result.

Results 1 - 20 of about 1,050,000 English and Spanish pages for radar detector. (0.13 seconds)

Ever heard of:

Safety Alert®????

You have a radar detector, read the instructions..

From the Cobra XRS-9300 model:

The XRS-9300 features 2 safety alert systems The Strobe Alert, a Cobra exclusive, works with tens of thousands of emergency vehicles currently equipped with traffic light controlling strobe emitters and the Safety Alert warns driver of emergency vehicles and road hazards from systems equipped with Safety Alert transmitters.

Ahhh, the power of Google.

Sorry to be a "smart ass"...

:D

Raul G

Following my previous post a little bit more: Since many motor vehicles are so soundproof that drivers often do not hear a train or siren approaching or see warning lights immediately, Cobra offers the Safety Alert(R) Traffic Warning system to help prevent possible accidents. When the XT-1000 Transmitter is installed on a train or such emergency vehicle as a police car or ambulance, it transmits special warning signals that can be detected up to one mile away by Traffic Warning Detectors. Detectors, installed in motor vehicles, warn drivers of upcoming hazards with one of three alerts: train (at an unguarded crossing), emergency vehicle, and road hazard.

And I don't work for Cobra.. Ha.

Raul G

the

Alert

Sounds like you have a crappy detector, responding to "out-of-band" signals like that. Field disturbance detector.

Same problem, telemetry this time.

More out of band response, DSRC toll interrogators.

Yes they have, and it is optical, not microwave. Would you like a link to the specifications?

See responses above.

alt.religion maybe?

Offhand i would say that there are some possibly seriously wrong assertions here.

1. In most jurisdictions law enforcement is not allowed to use preemption just to pull over someone for a traffic violation. Certainly not in California.
2. The red and blue strobes are not at the right frequency.
3. What encrypted signal? Peruse the device specifications. Want a link?
   formatting link
   It is an MSWord file

Joseph Barrett, P.E. California Department of Transportation Transportation Electrical Engineer

It is not in use in California that i know of, and I am in a position likely to know. Perhaps they are working with the local big city, Atlanta.

Was thinking of microwave security tag.