HF Maritime Communications
Revision as of 15:16, 27 August 2010
HF Maritime Communications
HF maritime communications can be found below 30 MHz. Here's a sample of what you can hear:
The HF Maritime Communications Receiver
A receiver for monitoring HF maritime communications must have the following
- Coverage from 100 kHz to 30 MHz
- Upper sideband (USB) and lower sideband (LSB) modes
- Good stability (doesn't drift off frequency)
- Good selectivity (able to seperate 2 stations that are close to one another in frequency)
Many receivers and portables marketed as shortwave or world band radios will satisfy
these requirements. The majority of voice communications use USB, but LSB is
certainly possible (foreign fishing fleets have been known to use LSB); therefore, whatever you
select must have USB and LSB capabilities. The lower band limit of
100 kHz is typical of many HF radios, but many marine transmissions occur
at 2 MHz and above. Other features such as memory channels and alpha tagging
are desirable, but not necessary. See the Receiver Reviews article for several links on this important topic.
Propagation and Antennas
Your ability to receive HF maritime communications is affected by signal propagation
conditions in the atmosphere. Many factors affect propagation, including sunspots, solar
flares, and the time of day. Frequencies above 10 mhz or so are usable during the
local daytime, while frequencies below 10 mhz will be usable at night.
If you are a newcomer to this topic, reading a good primer would be a great benefit. Don't
get discouraged about all the jargon; whole books and very technical scientific papers have
been written on the subject; but it's unnecessary to have a degree to gain a basic understanding.
To get you started, please see the Propagation Primer
website by Geoffrey Noles AE4RV (requires Flash player).
Your station is only as good as the antenna you can use. The best antennas for
receiving HF maritime comms is going to depend largely on what you can put up
and what kind of receiver you are using. Generally, something that is relatively broadbanded -
such as a random wire or inverted L - will be the best one to get you started. Our HF Antennas
page has a number of possibilities, including some that are already assembled - all you need to do
is supply the feedline and proper connectors.
If you live in an urban area, or are plagued with noise problems, consider utilizing
a loop antenna. MW DXers have been utilizing loops for their directional capabilities almost since
the beginning of the broadcast industy; they are useful for HF listening because they are less
sensitive to certain kinds of electrical noise. If you're interested in this topic, please
see our Loops page.
Another possibility is to use a Magnetic Longwire Balun(MLB) with a good grade of coax to feed an inverted L design. Plans exist on building baluns on the Shortwave SWL Antenna Yahoo group; or you can purchase the popular PAR EF-SWL antenna, which uses a similar principle. The HF Antennas article has information on these topics as well.
How to Find Activity?
The spectrum for HF maritime communications is very wide. Unlike VHF/UHF scanning, it's challenging to
automatically scan a segment of the band because HF noise will always be present. So, here are some places
to start searching;
- Numerous ship-shore HF frequencies exist in the 2, 4, 6, 8, 12, 16, 18 and 22 Mhz bands. Some are simplex (ship and shore on the same frequency) while others are duplex (ship on one frequency, shore on another). See this website for a complete list
- HFFAX.de Well known website run by Marius Rensen with extensive HF and satellite FAX information
- NOAA Maritime Products The place to begin to find schedules for SITOR and FAX stations from the US and elsewhere
- Dockside Radio Interesting place to find HF frequencies, both ham and marine for various support nets
- Digital and other modes
While many ships are now using encrypted digital signals for email and other traffic, there is still a great deal
of traffic in the clear. This includes SITOR-B weather broadcasts, FAX (Fascimile weather charts), GMDSS alerts
and more. Fortunately there are numerous software packages - some ham related, others not - that can decode some
or all of these modes. The list shown below is not expected to be complete, but is representative of what is
currently available. Where applicable, the link for the Yahoo support group for the software is also supplied;
Other Sources of Marine Related Activity
While some maritime stations are on a fixed schedule, others (such as fishing fleets) are much more
difficult to detect due to their transient nature; thus, listening for maritime comms can be
a game of patience. The more time passes, the harder it is to hear again. Mailing lists are one of
the best ways to keep ahead of what is being heard, as traffic can be passed relatively quickly.
The Utility DXers Forum is very active and is only one of many such lists; more are available on the Utility Monitoring page.
A few magazine publications have columns devoted to HF logs (including maritime stations)
submitted by readers. This is a great way to discover to what other people are
listening. These logs will often include multiple entries for the same
frequency, which means that frequency has been active. However, keep in mind
that, due to publishing constraints, there is often a 60 or 90 day lag between
when the report is received and when it's actually published.