I have two separate VHF radio’s on my boat each with their own dedicated 8-foot Shakespeare whip antenna. One unit is a older Uniden that I use as a back up, I purchased a newer Stardand Horizon a few years back so I would be set up with a unit that is DCS equipped. I live on James Island out close to Folly Beach and I’ve tested both radios using channel 27 the Sea Tow automated test on a regular basis. From the house going across the land to their station in North Charleston my transmission comes through fairly clear on both radios. A few weeks back we were offshore fishing and I noticed the radio seemed to be very quiet on 68 for a nice flat Saturday. I turned on the back up and it too was pretty quiet. We were in 90 feet of water when I became concerned that perhaps my radios were not functioning properly due to the air silence. I switched over to channel 27 and tried a radio check on both with no luck. I switched back to 68 when I heard someone calling for a radio check. I responded to their radio check and we both confirmed it loud and clear. I asked my responder for his position so I could get an idea as far as how long my transmission was going but no response. I guess my question is approximally how far away should I be able to get a clear response on the automated check on a good day? Hindsight I realize I should have requested another check when out there from another individual or at least tried the automated check at say 20-miles and 10-miles. I have since done the automated check from the house with the boat in the yard and it sounds pretty clear.