[Aavso-sid-list] What is the fastest frequency band for capturing onset of flare?

[Thomas Ashcraft]

Question :

In preparation for the new solar cycle,  I want to set up a solar x-ray 
flare detector to alert me immediately when a flare is in progress in 
order to capture video of a white light flare.  So then,  what frequency 
band is quickest to register the onset of a solar flare :  vlf or 
somewhere in the vicinity of 20 MHz decametric?

Thanks in advance for your experience.

Thomas Ashcraft