Reduce jitter in new cable modem's lead (6)
I believe the answer is:
'reduce jitter' is the definition.
(to calm or remove jitters)
'new cable modem's lead' is the wordplay.
'new' indicates an anagram.
'lead' says to take the initial letters.
The initial letter of 'modems' is 'm'.
'cable' is an anagram of 'becal'.
'in' is the link.
(Other definitions for becalm that I've seen before include "Leave (sailing ship) without wind" , "Make quiet or still - that's an order?" , "Leave a sailing vessel unable to move for lack of wind" , "don't get the wind up" , "Take the wind out of ones sails" .)