Characteristics of traffic radar

[Jan Panteltje]

I would do it differently. We don't need to transmit at 1GHz for
every car. Every car can install a $5 GPS receiver and transmit their
ID and location with less than 100 MHz.

Possible, but you also need multiple receivers, and it does not fix the trick
of speeding and then parking and having a cup of coffee to have exit time
- enter time of a road so average speed is < max allowed.

 

[linnix]

Possible, but you also need multiple receivers, and it does not fix the trick
of speeding and then parking and having a cup of coffee to have exit time
- enter time of a road so average speed is < max allowed.

Why not? In response to a request, the car transmits the position
every second and the receiver cop can calculate it's speed. The key
to this is a low cost precision gps receiver (accurate to cm). The
heart of this precision receiver is a stable Cesium clock. Sponser my
project and I will show that it can work.

 

[Jan Panteltje]

Why not? In response to a request, the car transmits the position
every second and the receiver cop can calculate it's speed. The key
to this is a low cost precision gps receiver (accurate to cm). The
heart of this precision receiver is a stable Cesium clock. Sponser my
project and I will show that it can work.

Yes that would work, using GPS,
but in my system the receivers are placed at every road, connected to a
central computer.
If you speed, you will be charged automatically every time.
No cops needed, other then coming to pick you up when your account reaches zero.
I am a bit reluctant to sponsor any of those systems.... freedom and ideas
like that.
Gov is starting to invade in a bad way all over the world.
In Germany now they want to give police the ability to search your PC online
(without your consent, so hacking it)...
Do you trust the police down the road with your banking password?
Where does it end? Brain implant at birth?
Oops, should not have mentioned that.

 

[linnix]

Yes that would work, using GPS,
but in my system the receivers are placed at every road, connected to a
central computer.

Mine too. I just said receiver cop, which could be stationary unmaned
receiver. We want to take the human factor out of traffic control.

If you speed, you will be charged automatically every time.
No cops needed, other then coming to pick you up when your account reaches zero.
I am a bit reluctant to sponsor any of those systems.... freedom and ideas
like that.

Our project is to build a precision GPS. How we use it is a different
story. It could be used as automatic cars or automatic bomb disposal
unit, but terrorist can also use it as car bomb. Knowing the risks
and benefits, it would not stop us from developing it. If anything,
we need better plannings and controls. Initially, the units are
tagged and controlled via the internet. It's a requirement to give
up your privacy to use such equipment.

 

[Jan Panteltje]

Mine too. I just said receiver cop, which could be stationary unmaned
receiver. We want to take the human factor out of traffic control.

I am surprised nobody noticed how fair this system is.
It favors the rich 100%

we need better plannings and controls. Initially, the units are
tagged and controlled via the internet. It's a requirement to give
up your privacy to use such equipment.

eh... you can only do that if you sort of assume the 'system is perfect'.
As the sytem is not perfect, it is better to keep some playing space.

 

[linnix]

I am surprised nobody noticed how fair this system is.
It favors the rich 100%


eh... you can only do that if you sort of assume the 'system is perfect'.
As the sytem is not perfect, it is better to keep some playing space.

It may not be prefect, but an improvement. The technology is already
there. The current system use a encrypted P-code, which is available
to government agents only (but spies as well). Our proposed system
use a stable clock source and remote processings via the internet.
The processing server can turn it off around sensitive area.

 

[Paul Hovnanian P.E.]

[snip]

So, just sample the IF at 10 Khz and FFT it.
What's so difficult about the filter?

My question wasn't about how to build one. It was to get some insight on
existing designs and their tradeoffs.

 

[Paul Hovnanian P.E.]

[snip]

Your questions were way to open-ended and no one feels like giving you a
treatise on the subject. Go look here:
http://www.copradar.com/preview/content.html

That's a non-technical summary of the subject as far as it goes. Most of
the interesting subjects are greyed out (no links to actual data).

 

[Barry Lennox]

[snip]

So, just sample the IF at 10 Khz and FFT it.
What's so difficult about the filter?

My question wasn't about how to build one. It was to get some insight on
existing designs and their tradeoffs.

IME, it's hard to get the info, I used to know a tech working on them
years ago, and he was bound by all manner of confidentiality.

Another suggestion may be to purchase a used one, there's adverts
around for them, and measure the characteristics.

Where is the investigation headed? Purely academic, or with an eye to
a countermeasures system?

Barry

 

[Paul Hovnanian P.E.]

[snip]

So, just sample the IF at 10 Khz and FFT it.
What's so difficult about the filter?

My question wasn't about how to build one. It was to get some insight on
existing designs and their tradeoffs.

IME, it's hard to get the info, I used to know a tech working on them
years ago, and he was bound by all manner of confidentiality.

Another suggestion may be to purchase a used one, there's adverts
around for them, and measure the characteristics.

Where is the investigation headed? Purely academic, or with an eye to
a countermeasures system?

Academic at this point. I wouldn't try to build any sort of jammer, but
understanding their shortcomings might prove useful in getting speeding
tickets thrown out.

They recently installed one of those traffic signs in my neighborhood
with the "Your speed is ...". It amazes me at how far off the mark those
things are under anything but ideal conditions (two or more targets for
example).

 

[Fred Bloggs]

Fred Bloggs wrote:

[snip]

Your questions were way to open-ended and no one feels like giving you a
treatise on the subject. Go look here:
http://www.copradar.com/preview/content.html

That's a non-technical summary of the subject as far as it goes. Most of
the interesting subjects are greyed out (no links to actual data).

It's good enough for your purposes. There are tens of thousands of
architectures for Doppler radar, but you are interested only in traffic
radar, and within that category, you are only interested in speed radar.
There is no requirement for coherence or even range determination there.
I would expect the simplest radar has no LO and does simple digital
oversampling of the audio difference frequency, allowing full digital
adjustment of the cutoff frequency high pass filter, set by the operator
in accordance with the speed limit excess to be ticketed. I would expect
that the FFT is amplitude qualified for maximum range and reports the
maximum speed within that window. It is up to the operator to eyeball
the scene and make the determination of the violator in the event of
multiple targets. Those crummy little roadside signs are turned way down
with a range of only about 50m on an average sedan and report the
maximum measured speed within their window, look to have an update rate
of about 2Hz. I doubt any of these systems "count" anything and there
can't be much dynamic range required for head-on RCS variation, I would
expect less than 6dB. If you need everything explained to you, maybe
it's over your head.

 

[YD]

Late at night, by candle light, Jan Panteltje

Yes that would work, using GPS,
but in my system the receivers are placed at every road, connected to a
central computer.
If you speed, you will be charged automatically every time.
No cops needed, other then coming to pick you up when your account reaches zero.
I am a bit reluctant to sponsor any of those systems.... freedom and ideas
like that.
Gov is starting to invade in a bad way all over the world.
In Germany now they want to give police the ability to search your PC online
(without your consent, so hacking it)...
Do you trust the police down the road with your banking password?
Where does it end? Brain implant at birth?
Oops, should not have mentioned that.

In Brazil someone came up with the idea of mandatory RFID tags in
cars. Ostensibly for locating stolen vehicles and automatic charging
in toll booths, but it's easy to see the real purpose, especially with
a cash-starved gov't with one of the world's highest tax rates and
least return. Just place a couple of receivers on poles a kilometer
apart talking to each other and time every car passing. A real cash
cow. Nothing will come of it, though. Vehicles more than 20 years old
are exempt from road tax, mine is 30.

- YD.

 

[Paul Hovnanian P.E.]

Fred Bloggs wrote:

[snip]

Your questions were way to open-ended and no one feels like giving you a
treatise on the subject. Go look here:
http://www.copradar.com/preview/content.html

That's a non-technical summary of the subject as far as it goes. Most of
the interesting subjects are greyed out (no links to actual data).

It's good enough for your purposes. There are tens of thousands of
architectures for Doppler radar, but you are interested only in traffic
radar, and within that category, you are only interested in speed radar.
There is no requirement for coherence or even range determination there.
I would expect the simplest radar has no LO

The local oscillator is the transmitted carrier. The I.F. is equal to
the Doppler shift of the reflected signal.

and does simple digital
oversampling of the audio difference frequency, allowing full digital
adjustment of the cutoff frequency high pass filter, set by the operator
in accordance with the speed limit excess to be ticketed.

Doubtful. If the 'setpoint' was 20 MPH and that adjusted the high pass
rolloff, then one could evade detection by driving sufficiently fast.

I would expect
that the FFT is amplitude qualified for maximum range and reports the
maximum speed within that window. It is up to the operator to eyeball
the scene and make the determination of the violator in the event of
multiple targets. Those crummy little roadside signs are turned way down
with a range of only about 50m on an average sedan and report the
maximum measured speed within their window, look to have an update rate
of about 2Hz.

They appear to have more capability than the handheld units. One feature
of even the cheapo sign units is that they can discriminate between a
single vehicle approaching or traveling away from the detector. If one
approaches the sign from the rear, passes it and then looks at it in the
rearview mirror, there is no speed displayed. This is not a capability
of most handheld units.

OTOH, multiple targets cause them to flip between clearly inaccurate
readings (from 20 MPH to 50 MPH instantaneously).

I doubt any of these systems "count" anything

That's probably correct. Although range determination would be
relatively easy to add with a freq. modulated carrier and some DSP
brains, the units don't appear to have any way to utilize this data,
even to inhibit possible interference due to multiple targets.

Oddly enough, there are radar detectors that can count the number of
emitters found.

and there
can't be much dynamic range required for head-on RCS variation, I would
expect less than 6dB.

Do you know that or are you just guessing?

Hint: Moving radar (which calculates both the police car speed and the
target's difference speed) discriminates between the two based on the
amplitude of the two Doppler signals. If the detector had this sort of
limitation, the difference in amplitude due to frequency response could
easily exceed 6 dB.

 

[Rich Grise]

The local oscillator is the transmitted carrier. The I.F. is equal to
the Doppler shift of the reflected signal.

When I was in the USAF, I had friends in the "Doppler Radar" department;
one of their components was "the audio amplifier".

Ever since I saw that, I've been wondering what it could possibly
sound like! ;-)

Cheers!
Rich

 

[Paul Hovnanian P.E.]

[snip]

When I was in the USAF, I had friends in the "Doppler Radar" department;
one of their components was "the audio amplifier".

Ever since I saw that, I've been wondering what it could possibly
sound like! ;-)

For traffic radar, it makes a whistling noise. Most CW* radar guns have
an audio output so the officer can monitor the signal. An experienced
operator can detect interference and judge target size and distance by
the volume.

*An interesting side note: Many years ago, I got a speeding ticket,
which I didn't think I deserved. Since I had a radar detector, I knew
when the officer pulled the trigger on the gun. It was a pulsed unit,
judging by the short duration of the detector alert. When I took it to
court, the officer read the usual BS about the radar unit model number,
that it was a pulsed unit, that it was calibrated within X hours using a
calibration tuning fork and that the officer had heard a continuous
Doppler tone and verified that there was no interference. On this last
bit, I asked how it was possible to judge interference by listening to a
short tone burst. He replied that the gun puts out a continuous tone,
regardless of the radar pulse length. I'm thinking that most pulsed guns
with speaker outputs synthesize the tone based on the speed reading and
it no longer has any correlation to the actual Doppler signal. Its just
there to make the cops happy. Or, the cop lied. In any case, since this
sort of reasoning is way over the heads of most judges, I got that
ticket.