Should you wish to enter the fascinating world of electronic espionage as a hobbyist then the only hardware you need is a short wave radio, preferably with an SSB or BFO facility. If you already have such a radio or intend to obtain one, the next step is to find out how and where to look for these Diplomatic, Illicit, and various other transmissions on the HF (High Frequency) wavebands.
There is quite lot of information about ‘numbers’ on the internet but here are a few examples for you to look at.
From experience I venture to suggest that the Enigma group is by far the best way for the beginner to get started on this hobby of listening to Spymasters sending coded messages to their agents in various parts of the world. All the information you will need is available through membership of this group.
The aim of this UK based online group is to bring together listeners and enthusiasts who monitor and gather information on 'Number Stations' and other related radio transmissions. Monitors can share their logs; discuss frequencies, thoughts and opinions on this most emotive subject.
ENIGMA 2000 maintains the ENIGMA Control List, the definitive listing of ‘number’ station identification and produces a bi-monthly newsletter giving details of frequencies of current stations whilst providing quality information on subjects not normally available from main-stream publications. The Newsletter can be downloaded from the ENIGMA 2000 group site. Members can also download it via the "Files" section of the same site. Also offered are written guides to finding and identifying stations complemented with a current selection of sound sample clips.
Should you be bitten by the bug and decide to set up a dedicated ‘Radio Shack’ in your home it would be preferable to have a desk top short wave receiver of which there are a number on the market both new and second hand. However should you simply wish to have a small portable receiver that you carry with you on holiday or elsewhere, string up a wire antenna and tune in, then one of the small portable, almost pocket size receivers will be fine. The one I use is a DEGEN1103, the reason being that it covers the whole short wave spectrum and has an SSB facility, essential if you want to listen to Morse code transmissions or some of the voice transmission using sideband. There are other receivers of this type available usually listed as ‘World Band Radios’ and offering the same facilities. Not all offer SSB however so it pays to check carefully before buying. It also pays to check if the receiver comes complete with a long wire antenna, not all of them do,