FX Chrony's don't work with fans????

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Saltlake58

Member
Apr 9, 2015
2,907
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Utah, United States
So, I'm tuning my gun in a wood shed. Everything is working just fine, no problems. Then . . . . .

It's hot today, so I turned the fan on.

Now, nothing works. The chrony hasn't moved, but it won't pick up the pellets and give a reading. So, I think to my self, it's Doppler Radar. Doppler measures changes in the air. Fans push air all over the place. Maybe I should turn off the fan (in fairness, it's a high powered fan to dry carpets). Magically everything starts working again.

Anyone else had problems with "Air Movement" impacting the FX Chronographs?
 
Pretty sure it's not the air movement unless the air is moving and flapping something solid. But the moving fan blades if hit by he radar waves can reflect back and "confuse" the signal processor.
Click to expand...

it's a squirrel cage fan (one of the round fans without blades) about 8 feet behind the table where I have the chrony setup. I fire away from the fan into the backstop. The fan is high velocity, puts out a lot of air. It's the type used for drying carpets.

If I remember correctly, Doppler Radar measures changes in air density or movement. (if anyone can correct that, please do!)

Anyway, all I know is fan is running, nothing shows up on chrony. Fan is off, chrony works. Considering the technical nature of Doppler Radar, I'll probably never really understand the cause, but knowing the fan impacts readings is the important thing.
 
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Radar waves get reflected from dense objects and the reflected frequency difference (doppler-effect) is processed to calculate distance and velocity. The FX Chono only calculates velocity and the object should be straight in front of the antenna to get accurate velocity results. If there are no moving parts in the fan exposed to the radar, what could be happening is that the air movement you are talking about has lots of small particles (saw-dust, pollen, metal particles, heavy water vapor) which are reflecting to the radar. Normally the air is not dense enough to reflect at such short distances. We are talking about a few feet. 

Take the fan outside to open space along with the FX chrono and try. 
 
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