Filtered connector

EE July/August 1986 62 38 filtered connector Computers and computer-driven peripherals are notorious sources of RF interference, and receiver jam- ming may occur at frequencies well above 100 MHz, even though the computer is said to run at a mere 16 MHz or so. The cause of this prob- lem lies in the very fast pulse rise time of the switching and timing signals internal and/or external to the computer system and its peripherals, which are often located well away from one another (printer, modem, mass storage). Much of the interference originating from long peripheral wiring systems may be suppressed quite effectively by inserting simple low-pass filters in the signal lines for data and hand- shaking. The proposed L-C filters are composed of small (3 mm) ferrite beads with 10 turns of 0.2 mm (36 SWG) enamelled copper wire, plus a ceramic 1 nF capacitor; the coil inductance is about 80 1.4H, which gives a cut-off frequency of about 60 kHz (120 Kbaud). The filters are mounted on a sma...