Subelement G: VHF-DSC Equipment & Comms— Topic :
Question 46G6
Element 7R (GMDSS-RO)What would happen if your VHF is set to “INT” and you called a VTS that operates on an “alpha” channel?
Explanation
When a VHF marine radio is set to "INT" (International) mode, it configures channels according to the international duplex standard, meaning it transmits on one frequency and receives on a different frequency for that channel number.
However, many "alpha" channels in the U.S. (e.g., 88A, 20A) are designated as *simplex* channels. This means the radio transmits and receives on the *same* frequency for these channels in the US. Frequently, the US simplex frequency for an "alpha" channel matches the international *transmit* frequency for that channel number.
Therefore, if your radio is on "INT" mode and you select a channel that is an "alpha" simplex channel in the US:
1. **Your Transmission:** Your radio will transmit on the international transmit frequency. If this frequency matches the US simplex frequency the VTS is monitoring, the VTS will hear your call.
2. **VTS Response:** The VTS will respond on its US simplex frequency. However, your radio, being in "INT" mode, is set to receive on the international *receive* frequency (which is different from the transmit frequency). Consequently, you will not hear the VTS response.
This makes option D correct. Options A, B, and C are incorrect because they misrepresent either your ability to hear the VTS, or the VTS's ability to hear you.