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Project Cohiradia

COHIRADIA is an acronym for CONservation of HIstorical RAdiofrequency bands by DIgital Archiving.

COHIRADIA has two main goals:

1. to give interested radio enthusiasts and collectors the opportunity to play back original radio signals recorded in the past on historical radio receivers. These signals should not contain only a single station, but a whole frequency band (e.g. medium wave) with all radio stations contained therein on the correct carrier frequencies existing at the time of recording. This allows all stations to be tuned-trough on the radio receiver.
2. to record currently broadcast radiofrequency bands, especially in the AM range, at various locations around the world. The goal is to map the still existing landscape of active stations in the form of archive files in time before the technology finally will die out.

COHIRADIA is made possible by recording and playing back digitized radio frequency signals using software-defined radios (SDRs). Wideband recording directly from an antenna is now relatively easy with several SDRs on the market, while playback requires more advanced SDRs with transmit output. The initiator of COHIRADIA uses the STEMLAB125-14 from RedPitaya, which offers a high quality for recording and playback with 14 bit ADC resolution and 125MS/s sampling rate. Alternative TX-capable SDRS with similar or better performance specifications also exist.

The recordings can be played back by anyone who also possesses a STEMLAB125-14 or a suitable TX-capable SDR. The use of a uniform data format guarantees interchangeability between different platforms.

In order to build up a rich archive in as short a time as possible, interested amateurs are invited to make their own recordings and to make the data available to the Radio Museum and/or to report on the successful playback of files on historical radio equipment. Creative ideas for other applications (activities, museums, ...) are also very welcome.

The oldest existing recordings on MW and KW were made by the initiator in the years 2006 - 2009 in analog form on a video recorder and digitized in 2021 with a STEMLAB125-14. On these recordings there are still many European stations which have been switched off in the meantime. All further recordings from 2021 on were produced directly digitally, mainly on long, medium and short wave up to 30 MHz.

For the playback of the data files as well as for the creation of own recordings on the STEMLAB125-14 a first software version was created in Python and is available for Windows10 as exe program. The author has already created a GITHub repository for the sources, a release as an open source project is planned for the near future.

• Descriptions for the installation of the necessary hard- and software are available at
  https://cohiradia.radiomuseum.org/download/docs/
• Furthermore the available software installation packages can be found at
  https://cohiradia.radiomuseum.org/download/software/
• Data files from archived recordings can be found at
  https://cohiradia.radiomuseum.org/download/data/

Hermann Scharfetter initiated and drives the project COHIRADIA. You can contact him via his profile to further develop the project.

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