I just used the Nav antenna with no modification. Theoretically you should shorten it to be optimum for the slightly higher Com frequency range but the gain realized is not worth the effort. By leaving it alone you have the option to use it as a Nav antenna in a later configuration where maximum sensitivity is more important. To really optimize the antenna for Com you would need to slightly change the tap point as well as the coupling capacitance associated with the tap. In real practice the noise level of the audio at the fringes of reception are not significantly different between the Com1 and Nav antennas to warrant retuning the Nav antenna.