75 Ohm antenna connector for Classe Tuner 1

I recently purchased a Classe Tuner 1 and a Radio Shack power FM antenna. The 75 ohm plug from the antenna when mounted onto the 75 ohm binding post of the tuner does not make a snug connection, and, therefore, I cannot tune to any signals. The circumferential dimension of the antenna plug appears to be too large and the axial dimension of the plug appears to be too small to make a reliable connection. I would have thought these connectors would be of a standard size but apparently they are not. Can anyone recommend a solution? I would appreciate your helpful comments.

Thanks.