11.5 Guide to MF/HF operation
Be aware of the following points when using the MF/HF radio equipment.
Frequencies available for communication are always changing.
Not all frequency bandwidths can always be used for communication.
After sending the DSC test call to a coast station, you will not always receive the
1. About the MF/HF radio equipment
Although for ship MF/HF radio equipment the 1.6 MHz to 27.5 MHz frequencies are
normally available, select an appropriate frequency from the frequencies assigned to
your ship for communication. As noted below, the use of the appropriate frequency
depends upon the radio wave propagation characteristics of the ionosphere.
Therefore, not all frequency bands are available for communication even if the
equipment is functioning properly.
2. Special characteristics of MF/HF radio wave propagation
As shown in the figure to the right, the
(path 1) and waves reflected from the
ionosphere (paths 2 and 3). You can
communicate using waves reflected from
the ionosphere and the earth because
the effective communication range of
terrestrial waves is limited
The available range of frequencies for
communication depends upon the radio
wave propagation characteristics of the
ionosphere. They will also change dramatically depending on the position and
distance from the station, the season, the time, and the sunspot number (approx. 0 to
250) which changes every 11 years
3. Selecting communication frequencies
MF/HF band communication frequencies cannot be predetermined. However, you can
select frequencies referring to previous communications logs, the frequency transition
table in this chapter under "Selecting communication frequencies in the MF/HF band
(reference)", and the radio wave propagation image.
4. About DSC testing
DSC operation is prescribed as an international standard
stations that receive DSC test calls should acknowledge the calls. Responses may be
sent manually instead of automatically depending on the equipment at the coast
station. It may take longer than expected to receive the acknowledgement even if
your equipment is functioning properly and you have selected the proper
You may experience skip zones where both terrestrial waves and waves reflected from the
ionosphere are unavailable at the end of the effective communication range of terrestrial
Radio wave propagation is affected by phasing, the Dellinger phenomenon, magnetic storms,
and atmospherics. Interference tends to be greater at night when radio waves can travel
ITU-R Recommendation M. 541
Ionosphere F1/F2 layer
Ionosphere E layer
Ionosphere D layer
of the ITU and coast