How to make a time machine for radio

Radio Spectrum Archive will give you to listen to old programs as if live

The recording spectrum on AM frequencies made on a VHS tape 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 time Witherspoon machine you can listen not only to the transfer, but the rest that were in the air: local news, advertising, pirate stations, even cryptic numerical station at short the waves.

Witherspoon's Time Machine is The Radio Spectrum Archive. Its creation was made possible thanks to 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 mainly 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 the 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. Many stations leave the air. ”

Witherspoon began collecting archival records from all over 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 each 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 size. 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 keep 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 an intermediate frequencybefore final tuning to the transmit frequency. In the analog era, shortwave enthusiasts discovered that they could connect to a radio circuit and record the intermediate frequency directly on 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 perform tuning 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-profit Internet Archive to store and share records. One of the problems is the need to dwell on a standard spectrum storage format. After that, there is hope for the creation of 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. ”