The aloft diagram is a accepted low-pass blast band clarify (L1,C1,L3,C2). L2 and L4 are bare aback we're ambidextrous with the 'Tip' and 'Ring' of a buzz band which may backpack up to 90VAC!.
I acclimated a agnate ambit on 3 phone-lines aback in the aboriginal 80's back I was active Scottsdale BBS and the filters performed fine. Additional advice can be begin in the ARRL Handbook, etc. For the two capacitors, the college the voltage the better, but the 400V types are the easiest to obtain.
Part and Descriptions
L1,L2 = 6.8mH, inductor
L3,L4 = 10mH, inductor
C1 = 0.022uF, 250-600V
C2 = 0.015uF, 250-600V
Via www. BenJammin.Net