Parts & Description
L1,L2 = 6.8mH, inductorL3,L4 = 10mH, inductor C1 = 0.022uF, 250-600V C2 = 0.015uF, 250-600V
The above diagram is a standard low-pass telephone line filter (L1,C1,L3,C2).L2 and L4 are needed since we’re dealing with the ’Tip’ and ’Ring’ of a phone line which may carry up to 90VAC!.
I used a similar circuit on 3 phone-lines back in the early 80’s when I was running Scottsdale BBS and the filters performed fine.Additional info can be found in the ARRL Handbook, etc.For the two capacitors, the higher the voltage the better, but the 400V types are the easiest to obtain.
This above circuit is © BenJammin.Net (Ben Kamen)