I know someone out here has done this already. Which is more accurate in real life conditions? A good radar is more expensive, but if GPS is only accurate to 49 feet RMS, how do they get a velocity accuracy of 0.1 knots RMS? (This is from the Garmin Etrex specs). It seems that they wouldn't even know you had moved until you move 49 more feet? They do state the velocity spec as being steady state. I am helping a friend test an upcoming speed device for the Prairie and I am in charge of the test equipment and setup. Any comments would be appreciated. Thanks.

 

A GPS gets their readings based on triangualtion from 3 or more satellites. Most GPS units have a 12 channel receiver meaning they can trackk up to 12 satellites at a time. The old ones were only 3 channel receivers and would lose their position easily.

I would have to say that the GPS would be just as accurate if not more accurate than a radar gun. Radar guns can be out of calibration, causing you readings to be skewed. I have heard of people contesting speeding tickets in court because the radar guns the cop had were out of calibration. Best part is HE WON. The radar gun in question was off by several MPH.

 

I would go with the GPS hands down. Actually I did, I bought the Garmin E-Trax just for speed testing, distance measureing and checking elevation. I think it works perfect. Mine cost $99.99 + $5 shipping and it had a $20 rebate on top of that. Total cost $85. I have used it so many times. Its a very valuable tool to me.

 

Does it state the precision? Accuracy would be the dead location, but if the GPS is consistently off by 49 feet, you'd still have a perfect speed rating. Then it would boil down to resolution (how far before it considers the next point unique from your location). I'm guessing the resolution/distance between unique points and the timing function generate the 0.1 knot RMS.

To ensure accuracy, just maintain a steady speed over as much distance as you can/as is reasonable, and that will remove the error from the GPS.

 

Thanks for the help!

 

I have both! A stalker radar and a etrex. If the etrex is gettinng a good reading it works just as well as the radar. In fact it will read in tenths, where as the radar will round down to the nearest mph. (This is done for court reasons) I have seen the Etrex read wrong, but it was in Battary saver mode. If you put it in normal mode and get good Sat. readings it will work just as good as a radar.