Centec Mill

Sieg SX3

HF Radio & decoding page


The photo here is my radio, an AOR AR5000 - it covers the radio spectrum from 10kHz to 2600Mhz in AM, SSB, CW & FM modes.

What is there to listen to?

The spectrum 0-30Mhz is split into four rough overlapping areas, a very short description follows - these are known as:

VLF - Very Low Frequency 0 - 60kHz

This range has some naturally occurring radio signals, long range submarine communications, maritime mobile, standard time and radionavigation signals.

LF - Low Frequency 60 - 315kHz

Time signals, radionavigation, maritime mobile, longwave broadcasting and Aeronautical Beacons.

MF - Medium Frequency 285 - 3025kHz

Aeronautical, Maritime, Military, Medium Wave Broadcasting, Beacons, Distress, Shipping and amateur radio.

HF - High Frequency 2850 - 30005kHz

Aeronautical, Maritime, Military, Short Wave Broadcasting, Beacons, Distress, Shipping, amateur radio and many others.

A full HF band plan is available here.

Above this is VHF - Very High Frequency 30 - 300MHz

UHF - Ultra High Frequency 300 - 900MHz

The VHF/UHF bands contain a vast selection of transmissions which include Civil and Military, Aeronautical, Broadcasting, Utility and many other services.

Above 900MHz is the Microwave spectrum. These are generally used as "line of sight" data/digital transmissions.

Amongst all these signals, a lot are transmitted in various "data" formats. If you've ever tuned a "Shortwave" radio you'll have heard all sorts of strange noises, some of these are data signals - they range from simple morse code to highly encrypted military signals.

Some such as RTTY (Radio Tele TYpe) and HF FAX are easy to decode and contain News, Shipping Information and weather reports. Some of the more exotic modes e.g. POL ARQ & SWEDISH ARQ usually contain diplomatic messages, some in plain language, some encrypted - these again are usually easy to decode - the content may not be! There are various military formats - some decodable and some that use digital spread spectrum techniques that are virtually impossible to decode. Despite the recent advances in digital satellite communications there is still a lot of data sent on HF.

What kind of equipment is required?

Apart from a HF radio with SSB (Single Side Band) , suprisingly little, there are lots of computer programs available that will decode the various signals, some use the PC soundcard input, some a simple interface connected to a comms port. There are also dedicated PC cards and external decoders.

Some of the more notable programs are Hamcom, JVFax, WXSat and RadioRaf. All are available from here.

Apart from data signals, a lot of plain voice radio transmissions take place. These range from International Distress & Rescue calls, to Maritime & Aeronautical Phone patches and all sorts of other calls. Some can be quite amusing, like a recently heard Russian Factory Ship ordering his supplies amongst which was 100 Kilo's of Cabbage and 200 condoms!

Some can be quite riveting, a call heard last winter was a lone skipper of a small powered sailing boat caught in gales in the Bay of Biscay. His engine had died, the wind was too strong for him to raise sail, and he was giving his position to Portishead in the UK every 3 hours while the storm lasted, on the understanding that if he didn't call in he'd sunk! He and the boat survived over 24 hours of gales and 5 days later he made it safely to Portsmouth.

One of the groups dedicated to this type of listening is WUN.

"The Worldwide UTE News Club (WUN) was established in January 1995. The purpose of the club is to further the exchange of information concerning the hobby of monitoring "utility" radio transmissions and stations that appear in the radio spectrum below 30 Mhz. Broadly defined, "utility" stations are non-broadcast stations, other than those in the amateur radio service".(Extracted from club charter).

They run a monthly newsletter and a listserver service where logs etc. are diseminated via email.

Futher details can be obtained from their web site.

If you have any questions about decoding data signals or HF radio listening in general please email me.

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Steve Blackmore

Copyright 1998 Steve Blackmore