Do I need a common mode choke at the feed point (transformer)?

No, we do not recommend any chokes at the feed point, especially coiled coax chokes, which actually might increase common-mode currents on any antenna feedline. But we strongly suggest installing the CMC at the entrance of your cable to the home in order to prevent any induced RF or common-mode noise signals from entering the home and interfering with your station and appliances. Note that all cables entering homes must be grounded before entering the home, and CMC should be installed between that grounding point and the antenna. See Grounding links in our tech library.