RE: Radar 101

[Thi VanAusdal <tvanausdal@xxxxxxxxxxxxx>]

> -----Original Message-----
> From: Luis Marques [mailto:marques@domain.elided]
> Sent: Monday, October 19, 1998 4:01 PM
> To: bmw-digest@domain.elided
> Subject: Re: Radar 101
> 
> Thi VanAusdal <tvanausdal@domain.elided> wrote:  
> > > and?  I am sure you know that the radar will pick up the target
> > > moving the fastest.  This changes at great distances, especially
> > > when there are other vehicles with considerably more 
> mass, (ie I may
> > > not pick up a speeding motorcyclye until it is much 
> closer than the
> > > cars it is approaching with, likewise I may not pick up a car at a
> > > great distance when it is surrounded by 18 wheelers.
> >
> > The 8 dB signal reflected off that semi coming at 55 mph
> > 800 ft  away?  The 7 db signal off that BMW going 80 mph at 200 ft
> > (and apparently ot paying attention!)?  Or the .5 db signal 
> from your
> > own heater blower fan spinning the equivalent of 110 mph?  
> C'mon, it's
> > the strongest signal, not the highest speed value! 
> 
> First of all, your heater blower fan is inside the car, so no 
> radar gun
> will ever detect it.  If you mean the auxiliary radiator fan, 
> the blades
> move perpendicular to the car's motion, so it will register a 
> speed very
> close to zero unless it is being targeted from the side - and then it
> will give both + and - speeds.  And it will be a very weak 
> signal since
> plastic doesn't reflect radar nearly as well as metal.

Point taken on an axial fan, but a squirrel-cage blower motor
mounted high in the cruiser's firewall is close to the source,
may reflect only one direction (top of fan, for instance), and
may be metal (a la 320i).  No, not really likely, you are correct.

> Second, newer radars can resolve between multiple targets and give you
> the speed of the fastest one.  While it is true that a strong radar
> return at any frequency will tend to mask any weaker frequencies close
> to it, if the two signals are far appart (in frequency), the stronger
> will not mask the weaker signal.  So if you are driving close to an 18
> wheeler going only 10mph faster than he is, you may be "invissible" to
> radar.  But if you are flying past him going at 130mph while 
> he's doing
> 75mph, the radar can lock on you no matter how big the truck is.

I assume they have some threshold values to determine signal strength
and
speed values to be displayed.  I did not even touch on signal masking,
and
I agree with the higher speed differential as being prone to targeting.
Not to mention patently unsafe anyway.  

This really sucks for us speeders.
 
> Although signal strength (target size and range) does matter, 
> the speed
> difference between the vehicles also plays a significant role and John
> Fountaine is correct when he says he can lock on a faster car 
> when there
> are other bigger cars around it going slower.
> 
> Luis Marques
> '97 328i

It is still up to the operator to determine which vehicle might be
displayed.

I think most of us take offense to the real or imagined scenario of
being
selected not by visual confirmation of speed and radar signal, but
because of
our '97 E36 :) '87 E30, or lime green Camaro versus another, less flashy
car.
I hate to drive 65, get passed by a hunter green Altima going 75, and
then
get HIS fucking ticket.   But that can happen, since policemen are human
(last I checked).  The problem we all have is with perceived malice,
bias,
or spite.  John F. has done his part to provide an example to the
contrary,
and that's great.

 - thi v.
Sold my copcatcherred '78 323i ...

"Cop didn't see it, I didn't do it." - George Carlin, c. 1990, Live at
the Met

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