Spies by the numbers

It's being reported that the activities of the alleged Russian spies arrested by the US included the use of shortwave morse code numbers stations.

Want to listen to spies?  According to a report by the UK's Southgate Amateur Radio Club, it's actually pretty easy to do.  There are a large number of broadcasts each day. In fact, there's probably at least one going on right now.

Equipment Required

First, you'll need a suitable shortwave radio, since "spy number stations" almost exclusively transmit on shortwave frequencies. If you already have one, you're probably all set. The basic requirements are that it is a "general coverage" receiver, capable of tuning between the allocated shortwave broadcast bands, to what are commonly known as the "utility bands". Most inexpensive shortwave radios are capable of this, except for the very low end models. This is necessary because most spy number stations transmit outside of the broadcast bands, although often close to the edges of the bands.  If possible, the radio should be capable of Single Sideband (SSB) reception. This is usually indicated by either the presence of USB and LSB modes, or a BFO (Beat Frequency Oscillator). Many spy number stations transmit in sideband, and most others are often best received in sideband mode.  An outside antenna is always preferred for best shortwave reception. If this isn't possible (due to apartment or townhouse rules, for example), an indoor antenna can still be used.

Stalking Your Prey

In general, most spy number station broadcasts start on the hour, with very few starting at the half hour, or even quarter after or quarter till the hour. So the best time to listen is starting just before the hour. Why just before? Many spy number stations will put their carrier on the air before the broadcast begins. Some have been known to put a carrier on the air hours before a broadcast starts. So be suspicious of open carriers, especially on or near hot number frequencies.  Here in North America, the most commonly heard spy number stations are probably the "SS/YL/5FG" stations.

Station nomenclature

A brief explanation about the naming nomenclature of these stations: the general format is language/gender/group size. The SS means Spanish, other possibilities are EE for English, or GG for German. Other less frequently heard languages include Chinese, Russian, Czech, Polish, etc.  The YL refers to the sex of the voice, YL is female (a ham radio term, meaning Young Lady) and OM is male (another ham radio term, meaning Old Man).  The 5FG means that the groups are transmitted in five figure words, that is a string of five  numbers. Other common formats include 4FG for four numbers, and 3/2FG which is a particular case of five figure words with a pause between the third and fourth numbers. Some stations don't transmit numbers, but instead use Phonetics, which are words that stand for letters, such as Alpha for A, Bravo for B, etc.