I have been intending to build this project for some time now and with the need for a balanced feed for the Doublet it was a good reason to go ahead with it instead of using a balun. It is based on the “S” Match ideas of PA0FRI and it’s application by RZ3AE. Instead of using the recycled ferrite tubes from printer cables I have used the items noted in the “Tube Baluns” article by OH1AYR. These tubes, Wurth 74270057, are available from RS Components. The following images help explain how to build the “S” matcher.
The binocular transformer. Two ferrite tubes are bound together and two lengths of RG213 are fixed inside each tube. The exposed outside cover of the RG213 is stripped off leaving the braid exposed.
The exposed braid is separated and joined at this end of the transformer. The centre conductors of the RG213 are connected to the Inductor binding posts.
The exposed braid is separated at this end of the transformer and joined to two wires connected to the PL259 socket (Tranceiver). The centre conductors of the RG213 are connected to the Capacitor binding posts.
A surplus aircraft radio Rotary Inductor is connected across the left hand binding posts. A 500pF variable capacitor is connected across the right hand binding posts. This completes the build.
Note that the capacitor body is live and needs to be isolated with an insulated shaft coupling and plastic bolts.
The Rotary Inductor’s body needs to be earthed.
All done. Found that I could match all bands, including the WARC bands, on the Inductor terminals. The capacitor terminals could be needed with a shorter aerial.