HF Military Communications
HF Military Communications
HF military communications can be found below 30 MHz. Here's a sample
of what you can hear:
The HF Military Communications Receiver
A receiver for monitoring HF military 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 (the Mexican Army is famous for this); therefore, whatever you
select must have USB and LSB capabilities. The lower band limit of
100 kHz is typical of many HF radios, but most military 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 category for several links on this important topic.
- What about digital modes?
The military utilizes numerous digital modes, only a few of which can be decoded
by software available to the general public. However, a mode often referred to as
Automatic Link Establishment (sometimes also written as MIL STD 188-144A) can easily be decoded. This software is often used to test the radio path between 2
stations, and on occasion, pass simple messages. See the ALE page for decoding
software - including some freeware.
Propagation and Antennas
Your ability to receive HF military 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 military 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 military 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 for HF military communications:
Aeronautical Off Route Sub-Bands
These bands have been designated for aircraft usage with a channel spacing of 3 kHz. HF military
communications will typically occur in these band segments.
- 3025.0 – 3155.0 kHz
- 3800.0 – 3950.0 kHz
- 4700.0 – 4750.0 kHz
- 4750.0 – 4850.0 kHz
- 5450.0 – 5480.0 kHz
- 5680.0 – 5730.0 kHz
- 6685.0 – 6765.0 kHz
- 8965.0 – 9040.0 kHz
- 11175.0 – 11275.0 kHz
- 13200.0 – 13260.0 kHz
- 15010.0 – 15100.0 kHz
- 17970.0 – 18030.0 kHz
- 23200.0 – 23350.0 kHz
Customs Over The Horizon Enforcement Network (COTHEN)
USAF High Frequency Global Communications System
Other Sources of Military Related Activity
Unlike broadcast stations, knowing when a military station is going to be on
the air is a game of patience; thus, any reporting of activity is very time sensitive.
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 military logs
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.