In order for successful communication between two MF/HF radios, the transmitter and receiver on each item of equipment has to be tuned to the correct frequency. Ship-to-ship frequencies (simplex channels) are not numbered. Frequencies designated for ship-to-shore communication (duplex) have attributed channels and are numbered in the following way:
1. band (2, 4, 6, 8, 12, 16, 18, 22, 25 MHz) to which belongs frequencies constitute first one or two digits of the channel number,
2. two following digits constitute successive channel number in this band e.g. CH 401 is first channel in the band 4 MHz, CH 1227 is 27th channel in the 12 MHz band.
On MF/HF radios channel numbers are usually entered via a numeric keypad.

Practise on a MF/HF radio simulator

Press the Ch button, key in an existing channel number and press the SAVE softkey.

User channel

Some MF/HF radios are supporting user channels. User channels are programmable channels that can be accessed as easily as other channels. Programming users channels is reasonable when specific frequencies are used often.

Practise on a MF/HF radio simulator

On MF/HF radio 199, user channels from CH 1 to CH 199 are programmable.

• To select an existing channel press the Ch button, key in a channel number between 1 and 199 and press the SAVE softkey.
• To store a non-existing channel, select the desired Rx and Tx frequency and mode, press the Ch button, key in a channel number between 1 and 199 and press the STORE softkey.
• To replace an existing channel select the desired Rx and Tx frequency and mode, press Ch button, key in a channel number between 1 and 199 and press REPLACE softkey.
• To delete an existing channel first select the channel by pressing Ch button, key in the channel number between 1 and 199 and press the DELETE softkey.
  

On MF/HF radio channels these can also be allocated to stations through the STATIONS option in the menu.