Text 16257, 191 rader
Skriven 2005-11-14 22:25:49 av Raymond Yates (1:3613/48)
  Kommentar till text 16191 av Michiel van der Vlist (2:280/5555)
Ärende: looters in NO
=====================
 MvdV>>>>> But the reflected signal will be 20 to 40 dB weaker than the
 MvdV>>>>> direct signal. That means you have to get a lot closer to
 MvdV>>>>> detect it.

 >>>> That'd depend on the sensitivity of the detectors front end.

 MV>>> No, it doesn't. The difference in signal level depends on a lot
 MV>>> of things, but the sensitivity of the receiver is NOT one of
 MV>>> them.

 >> I almost hate to get into the middle of this, but I will,
 >> anyways. <g>

 MV> Don't say you haven't been warned... ;-)

Yeah, you'd think I would know better by now.. ;-)

 >> North Carolina is one of those states that allows the use of
 >> radar detectors.

 >> I've used them for years. At one point I had two differet
 >> models in my car for comparison purposes. I found I could pick
 >> up the side and rear lobes very well, at different ranges with
 >> either unit, well before entering the detection zone.

 MV> That makes me wonder how you know ehere the detection zone starts. If
 MV> you can pick uo the signal reflecting from objects, why can the
 MV> reciever in the speed trap not pick uo that same signal end use it for
 MV> measurement?

THe detection zone being, for example, whe the Police car is around a curve,
and you as the target are outside the 5 degree legal maximum amount of
deflection (car cannot be more that 5 degress off the highway, I don't know
why, but it's the law) In teh case of reflections, we're talking about a
transmitted signal, not the signal reflected back, which may or may not be
recievable, but would seriously be attenuated.

 >> The difference was in the front end recievers, which is
 >> what Roy was trying to explain.

 MV> Roy was just trying to contradict me. You know Roy...

Ok, than what I was trying to explain, here.  I took it as a serious attempt
to communicate. the reciever sensitivity is a crusical issue. Early models
were not so good, and they have improved over the years, just in time for the
lasers to replace radar in many places.

 >> In the case of encountering the front lobe, one unit was
 >> signifcantly better than the other, having nearly twice the range.

 MV> All very weel, buy the *difference* between direct and reflect3d
 MV> signal would still be 2- tp 40 dB. With both receivers. Althouf the
 MV> better receiver would detect the trap form a greater disctance, you
 MV> would still have to come a lot closer when detecting if from the back
 MV> then when detecting it from the front when one is in the main beam.

Yure. but that fact that you can detect it at all from the back gives one the
advantage in that you know it's there before you hit the main beam and get
documented. It's close, Yes, but any advantage is a good one.

 >> True, the signal level reamins constant, but the ability of
 >> the reciever to detect that signal is critical. That /is/
 >> a function of the electronics, obviously.

 MV> Obviously.

 >> After I was done with the comparison, I placed the weaker of
 >> the two recievers facing towards the rear of the vehicle. I
 >> figured that if the police can mount two transmitters one
 >> facing forward and one facing rearward, the least I can
 >> do is set recievers to match. <g>

 MV> Ah, yes. That would be usefull when speeding in reverse... ;-)

No, it's useful when the poilce car has forward-looking radar. Hey do that
here. Most of the city radar unist have a permanently mounted unit in the
front and rear window. other tactics used have been using a hand-held unit in
a paper bag held by a homless-looking person, the hand-hled up in a city
bucket truck at stop-light level, and near a golf-course next to a school, in
a golf cart by an appropriately attired driver. The latest was an officer
dressed in a chicken suit standing by the side of the road.

 >> Oh. I could pick up radar transmitters on stores, up to a
 >> half-mile away..

 MV> That is pretty good. Much better than I expected. I wonder why they
 MV> need such strong transmitters for a door opener.

That's a very good question !

 MV> Over here radar is not used for door openers btw. All these detectors
 MV> are passive infrared.

A lot of them are here as well as they are cheaper. but, the radar still is
used a lot.

 >> In my area, I have a four-lane highway I travel six times a
 >> week at minimum. It's the only road to town, there is no choice.
 >> The posted speed limit is 55mph (88kph_). Nearly everyone without
 >> exception travels faster than that, usually 65mph (104 kph) to
 >> 70mph (112 kph) at all times, day or night. Now were I to travel
 >> at teh posted speed limit I would be impeding  traffic in the
 >> practical sense.

 MV> We had similar situations with the 100 kph general speed limit some
 MV> 15, 20 years ago. Few observed it and it wasn't enforced.

 MV> Then they raised the general speed limit to 120 kph and said that
 MV> *this* limit would be enforced. And they did. aqnd it worked. Speeding
 MV> is much kess seen that it was 15 years ago. Most people now observe
 MV> speed limits here.

Well, if the speed limits are sensible, that works.

 >>>> Wanna bet? I've seen youngsters jump from lane to lane, cutting
 >>>> people off and causing accidents behind them in traffic jams.

 MV>>> Not possible in the traffic jams they have here. In such a jams
 MV>>> cars are bumper to bumper at walking speed or are at a complete
 MV>>> stop. One can not "jump form lne to lane", there is simply no
 MV>>> room to go anywhere but go with the flow.

 >> Roy's describing the other type of traffic jam, the one at speed.

 MV> In that case we do not call it a traffic jam, that's just heavy
 MV> traffic.

OK, different terms from different locations..

 >> I have been in traffic at speed in the morning rush hour where
 >> everyone is traveling 70mph (112kph) excpt for a few idiots
 >> that jump from lane to lane in the attempt to go faster than
 >> the average. Tha's what roy is describing, the "at speed" traffic
 >> jam. I don't know if you have ever experienced this or not,

 MV> Sure, what you describe is more or less the normal situation during
 MV> the rush hour on the motorways here.

It can be vary scary when these guys travel in groups, which is becoming more
and more frequent. We have several modified Toyota and Honda car clubs, you
knwo the "tuner cars"? they get out on hte 2-lane roads here and act really
stupid.. 100 moh speeds on 55 mph roads, cutting around traffic in groups, we
try to get them ticketed when we can..The Highway Patrol is very aggressive
with them..

 >> but ti's different from the stopped traffic jam which we call
 >> "gridlock", whether it's in a city or not(the precise term gridlock
 >> referes to traffic in cities where the cross streets are also
 >> full of stopped traffic, but the term is used to generically
 >> describe any traffic that is immobile).

 MV> Such a situation often occurs here. Not just in the cities, but also
 MV> on the motorways. often because of an accident. Or a situation where
 MV> to roads come together. In the latter case, traffic will still be
 MV> moving, but ever so often it slows down to a crawl.

Last time I went to Raliegh on the four-lane there was an accident and traffic
was backed up ten miles.. moving at a stately 3 mph. It's not uncommon for the
only bridge into Wilminton to be raised in the middle of rush hour traffic and
that causes a serious backlog, often five miles or better. Once the bridge is
lowered it clears fairly quickly. 30,000 vehicles us that bridge each morning
and evening..

 MvdV>>>>> Plus that the methods of detection have improved to the
 MvdV>>>>> point that there is no escape. The latest system is "traject
 MvdV>>>>> controle". Camaras at checkpoint A record you time of
 MvdV>>>>> passing and then when you pass checkpoint B five kilometres
 MvdV>>>>> further down the road you are clocked again. Arrive their
 MvdV>>>>> too early and you get the ticket in the mail.

 >> The New York State Thruway was doing that in the 1950's, where
 >> they ticket you had picled up at the entering tollbooth had
 >> your starting time stamped on it. When you turned it in topay
 >> your toll, the tolltaker would check the time (the computer
 >> did that) and tell you what your toll was while the machine was
 >> printing out your speeding ticket.

 MV> Over here they now have it perfected to the point that there is no
 MV> human involved. The camera sends its images to a computer that
 MV> extracts the license number on the plates from the pictures. The
 MV> computer sends the speeding ticket. Only when someone contests it,
 MV> will a human look at the pictures.

 MV> Cheers, Michiel

 MV> ---
 MV>  * Origin: http://www.vlist.nodelist.org (2:280/5555)


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