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dr.freestyler
08-02-2006, 11:21 PM
I was at the legg mason tourney and they had one of those small tents w/ a radar gun. I'm curious how accurate these things are, cause this kid (like 14) went before me, served in the 60/70 range, then a few people went, then myself, the best i could do was low 90's. The kid then says to his dad, that he thinks that if you hit the ball toward the gun, it seems like those readings are artifically higher than otherwise. He goes back in, and aims right toward the gun, and all of a sudden he is hitting the low 90's, and clearly not hitting any harder then he did before.

So are those radar guns meaningless, or was it just the setup here.

spaceman_spiff
08-03-2006, 12:29 AM
I was at the legg mason tourney and they had one of those small tents w/ a radar gun. I'm curious how accurate these things are, cause this kid (like 14) went before me, served in the 60/70 range, then a few people went, then myself, the best i could do was low 90's. The kid then says to his dad, that he thinks that if you hit the ball toward the gun, it seems like those readings are artifically higher than otherwise. He goes back in, and aims right toward the gun, and all of a sudden he is hitting the low 90's, and clearly not hitting any harder then he did before.

So are those radar guns meaningless, or was it just the setup here.

Actually, the kid just knew the right strategy, and if you were to hit right at the gun, your speeds would be much higher. An old fashion radar gun only measures speed in one dimension, which means it is only accurate if something is travelling directly towards it or away from it. If the object is travelling at an angle relative to the gun, you are always going to get readings that are lower than the actual speed, because the gun is only measuring the one dimension toward or away from it.

All of the new guns that use phase array technology are much more accurate, because they measure speed in all three dimensions. This way, even if the ball is travelling at an angle relative to the gun, the speed is not dramatically underestimated. The good phase array guns measure speed within about 1 or 2 mph.

tennis-n-sc
08-03-2006, 04:02 AM
Actually, the kid just knew the right strategy, and if you were to hit right at the gun, your speeds would be much higher. An old fashion radar gun only measures speed in one dimension, which means it is only accurate if something is travelling directly towards it or away from it. If the object is travelling at an angle relative to the gun, you are always going to get readings that are lower than the actual speed, because the gun is only measuring the one dimension toward or away from it.

All of the new guns that use phase array technology are much more accurate, because they measure speed in all three dimensions. This way, even if the ball is travelling at an angle relative to the gun, the speed is not dramatically underestimated. The good phase array guns measure speed within about 1 or 2 mph.

Great description of the old radar, which I have used extensively.

spaceman_spiff
08-03-2006, 04:44 AM
Great description of the old radar, which I have used extensively.

I think you might find an archived article in Tennis magazine that really discusses it much better. Still, you can get the general idea.

dr.freestyler
08-04-2006, 01:03 PM
wow, thanks, that really makes sense. Cause i started thinking i need to change my serve to get some more power, but i swear i can hit it in the upper 90's to low hundreds on the first which i am ok with for now.

chess9
08-05-2006, 01:31 AM
Yes, the old guns use a simple Doppler technology that is accurate to about 10% or so as I recall. I've found that with my radar gun the fastest serves are the ones the go right over the top of the gun.

-Robert