How to make a time machine for radio

Radio Spectrum Archive will let you listen to old programs as if it were live.

The spectrum of recording on AM frequencies made on a VHS film in 1986. You can clearly distinguish the individual stations in the form of peaks scattered over the digitized record.

Thomas Witherspoon makes a kind of time machine. With it, you can select a date and listen to the radio program as if you have a radio capable of receiving programs from the past. Of course, popular shows have access to their previous episodes, but with the help of Witherspoon’s time machine, it will be possible to listen not only to these programs, but also to all the others that were on the air: local news, advertising, pirate stations, even mysterious number stations on short the waves.

Witherspoon's time machine is The Radio Spectrum Archive . Its creation was made possible by the proliferation in recent years of cheap software-defined radio systems (POR), capable of digitizing huge amounts of radio frequency spectrum. POR software can be used to select individual programs and listen to them live. Or, you can record the entire spectrum and play it with the program later, giving listeners access to the programs as if they are only now.

Short-wave listeners and radio amateurs used POR in the main to search for interesting signals, “but few people thought about the possibility of preserving the spectrum and archiving it. However, some people thought, “- says Witherspoon. Part of the motivation was an interest in how radio changes in the Internet era: “Transmissions on AM frequencies in the USA, on FM frequencies and on a short wave vary greatly. A lot of stations leave the air. ”
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Witherspoon began to collect archival records from around the world: for example, once a year he meets a friend who comes to the United States from Australia. "We take every 2-3 TB on a hard disk, fill it with records, then meet and exchange."

The biggest obstacle to Witherspoon's plan for collecting a large number of records and putting them online is their volume. The team in particular copes with this by keeping records related to interesting events. “For example, when there were negotiations with North Korea, we recorded the AM-range programs. But since the news did not change much during the day, we decided to save only the two-hour segment. ” Witherspoon assumes that they now have 150 TB of records, “combed to the state when they should be loaded”.

Some of them go surprisingly far into the past. Usually, the radio received carrier signal is shifted to the intermediate frequency before the final tuning to the transmitting frequency. In the analog era, shortwave enthusiasts discovered that they could connect to a radio circuit and record the intermediate frequency directly to an analog hi-fi VHS film (its bandwidth allowed us to record this signal). Enthusiasts did this to hunt for distant radio stations. By recording a spectrum, they could later play the recording through their radio. As a result, they could tune in as many times as they like to hear the identifiers of all stations announced at the beginning of each hour. Some of these films have survived - for example, a film from Rhode Island, which recorded the AM band on May 1, 1986, when the first news of the Chernobyl tragedy began to leak to the West.


The Radio Spectrum Archive is now working with the non-commercial Internet Archive to store and share recordings. One of the problems is the need to dwell on a standard spectrum storage format. After that, there is hope of creating a web interface that allows you to study the records and play them. Witherspoon is looking for volunteer developers to work on the interface.

Witherspoon believes that over time, the value of The Radio Spectrum Archive will become increasingly apparent. “For this reason, I'm losing the 1986 recording. It gives us a sense of temporary distance so that we can see its value. ”