On a single frequency receiver the user can switch to the 490 kHz frequency for reception of a message (at a scheduled transmission time) and then switch back to the 518 kHz frequency when the message has been received. On a dual frequency receiver this is usually by default enabled to receive on both frequencies: 518 kHz and 490 kHz. However, one of them or even both may be omitted.

Practise on the NAVTEX receiver simulator

The simulator is simulating dual frequency receiver, so default setting to receive both frequencies may be changed. Go to the Setup Mode -> NAVTEX View -> Options Page, navigate to the NAVTEX Frequency setting and press RIGHT/LEFT navigation key to change the setting.