Did you account for the 'cosine' factor?
At long range the cosine error will be small.
As you pass right by the sign, the error will be significant
since the doppler reading will not be along the vector of your
motion.

If it's reading HIGHER than your real speed, then the
sign is crap since the cosine error will always make you
look slower.

As as aside, I have found that my GPS speed and vehicle
speedometer were in close agreement above 80 km/hour, but
as slower speed the speedometer read proportionally high (5-10kph).
I wonder if this is deliberate in the firmware since it's an electronic
speedo (Chrysler Voyager, '93) so should have no non linearity.

R

Dave VanHorn wrote:
>>
>> That said, there is no doubt that the machines DO work most of the time
>> very well.
> 
> My local department bought a few of those K band speed boards that 
> display your speed..
> 
> I decided to do some testing.
> 
> The target is a 1998 ford expedition, it certainly shouldn't have any 
> trouble seeing that, especially on such a long straight road, with no 
> other plausible targets in sight.
> 
> I just waited till a nice quiet time of night, and made speed runs 
> calibrating against my GPS.  At 40 MPH nominal, my displayed speed was 
> about 10 miles off, in both directions sometimes, and most times was at 
> least 3-5 miles off.
> 
> GPS guarantees 1MPH accuracy.
> 
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