ICOM m803 - difference between antennas?

[suiramor]

ICOM m803 has two outputs for antenna connection: one goes to the AT-140 and the other is described as 'HF Antenna for DSC comms'. What's the difference in use and deployment? I have the first one connected through the AT-140 to my isolated backstay. What kind of antenna do I use for the 2nd? What does it give me if it is connected? Could I connect it to the VHF antenna used by my other VHF radio (without blowing both and/or the boat up)?

[Wotname]

The second antenna is a receive only antenna. It only functions for some DSC HF operations. It allows the receiver to continue receiving while the transmitter is transmitting.

Most times recreational sail boats do not use the HF DSC functions and most do not worry about the second antenna. The second only needs to be a long length of wire.

Do not connect it to the VHF antenna.

[Jammer]

The second antenna is a receive-only antenna that the radio uses to monitor the frequencies used for DSC in each band. If it is not connected, the radio will not receive DSC. My understanding isn't clear on whether it will receive DSC acknowledgements for DSC messages that are sent -- the transmit goes on the main antenna, not sure about the response.

Usually people connect it to a 5' to 10' whip antenna. The antennas sold for Weatherfax use are ideal and are about 5'. CB antennas will work OK. VHF antennas are generally too short to be effective. As Wotname writes, you can also make a wire antenna.

A fact to consider is that a really good DSC antenna will receive mayday calls from a great distance, far beyond that where your vessel would be a plausible candidate for providing aid. The DSC mayday calls that you could then receive may become a distraction from other important responsibilities. In that light it is important to select an antenna that has sufficient but not excessive performance.