I built a common mode choke / 2017-09-08

After the problems with the laptop controlling the radio when I participated in the SCC RTTY contest 2017 I decided to build a common mode choke. This is a filter that should keep the radio frequency signals at the side of the antenna.

Based on the simple design with a piece of PVC pipe with 8 windings of Aircell-7 coax I still had lying around. The PVC pipe was donated by a fellow radio amateur who had it in his junkbox.

I drew a pencil line on the pipe, decided where to drill holes for the coax cable (using a 16 millimeter drill) and where to drill holes for tiewraps to hold the coax. After drilling the holes it was a matter of winding the coax correctly, mounting the cable with tiewraps and soldering the connectors to the cable.

In the first testing the filter worked fine, completely stopping the interference to the keyboard of my "shack computer" and even reducing incoming noise on the 10 meter band.

Common mode choke: materials

Common mode choke: finding where to drill holes

Common mode choke: holes drilled

Common mode choke: cable mounted

Common mode choke: connectors done