That appears to be our baby.
nite
Sparrow missiles require a special Radar illumination called Pulse Doppler Illumination (PDI). The Radar illuminates the target with PDI during the pre-launch attack phase when Sparrow is selected, the target is within 1.2 times Rmax, and the Radar has adequate target signal strength for a steady track. This signal informs the Radar to use PDI when possible. When the Radar is transmitting PDI, PDI is displayed in the PRF window on the Attack Format at [PB1]. This provides feedback on the target tracking capability of the Radar before launch.
https://forums.vrsimulations.com/support/index.php/AIM-7_Sparrow