The ART-2000/2100 has a dipswitch with eight settings used for installation functions. The dipswitch must have the correct configuration for the radar to recognize the size of the installed antenna. Please see the images below to locate the dipswitch on your unit.

If a 10" antenna is being installed, the #4 Switch & #5 Switch must both be in the "ON" position. If a 12" antenna is being installed, the #4 Switch must be in the "OFF" position & the #5 Switch must be in the "ON" position. The setting is on when the switch is positioned towards the center of the unit.