We had a similar issue on our SM. Limited distances in terms of transmission (less than a mile), as well as reception. I assumed it had to be the antenna, but after much trouble-shooting, we figured out it was the radio itself (a Simrad, about 15 years old). A new radio fixed the problem.
One other place to check the antenna, however, is at the base of the main mast. I don’t know if the 54 is the same as a SM, but there is a connection there between the coax coming down the mast, and the coax coming from the VHF. Ours was somewhat corroded. However, fixing that did not help much.
We bought a Garmin 300 and have been very happy. It has an “active” speaker that goes in the cockpit (a volume knob on the speaker), so that the helmsman can hear transmissions, but those below can sleep in relative silence. There is also a remote handheld unit that pairs with the nav station VHF for use without having to go below.
Aletes SM 240
St Augustine, Florida