3 ms·

Nice bit of reverse-engineering, and an impressive hack from whoever built the system.

jrockway 13y ago
Not really a hack. Subcarriers are how they added color to TV, stereo to FM radio, and so on. WWV/WWVH also sends machine-readable time codes at 100Hz like this.
- jzwinck 13y ago
  Indeed--it was more of a hack sixty years ago perhaps. Since then, similar tricks have been used for closed captions, Dolby surround (the original kind), Radio Data System (which puts song names on your car dashboard via FM radio), TV Second Audio Program (listen to shows dubbed in a second language, just press the SAP button on your ancient high-end TV!)....
  - jahmed 13y ago
    Wow. I always thought SAP stood for Spanish Audio Program. TIL.
- EEGuy 13y ago
  >Subcarriers are how they added [...] stereo to FM radio... Set your time machine for 1958, or follow this link [0] to see how RCA did both FM stereo (throughout the article they call it "multiplex") and 67 KHz "SCA" subcarriers. Admire the awesome 5KW FM transmitter cabinetry and transformer shielding. [0] http://fmamradios.com/BTE-10B.html http://fmamradios.com/BTE-10B.html
  - jrockway 13y ago
    One thing I find particularly interesting about articles from this time period is that Hz is not yet the name for 1/s, and so everything is in "cycles per second". According to Wikipedia, the transition started in 1960, so we're two years away when this article was published.
the-kenny 13y ago
Quite funny - I know someone who uses a similar setup to send GPS Coordinates for a Quadcopter and a Plane via the audio channel of the video link (he flies the Quadcopter/Plane with video goggles) to the ground station. There, an Arduino controls some stepper motors to point directional antennas at the copter/plane. Project is at https://github.com/KipK/Ghettostation https://github.com/KipK/Ghettostation - video at https://www.youtube.com/watch?v=tiO4YCX7hJo https://www.youtube.com/watch?v=tiO4YCX7hJo - you can hear the modulation in https://www.youtube.com/watch?v=nm0okv8mTsg https://www.youtube.com/watch?v=nm0okv8mTsg
- bri3d 13y ago
  Cool! I hadn't seen that project before, although I'd seen a few other telemetry-over-audio solutions. They usually use simple FSK just like the "real life" helicopter in the article. Here's an example of a common simple protocol: http://www.flytron.com/pdf/audio_modem.pdf http://www.flytron.com/pdf/audio_modem.pdf
anigbrowl 13y ago
Using spare audio capacity like this is actually very common - prior to digital recording, engineers would dedicate one tape channel to recording a sync signal, and in mission-critical applications would even 'stripe' the tape with the sync signal beforehand (many pro recorders can have recording and read heads active simultaneously).

Not really a hack. Subcarriers are how they added color to TV, stereo to FM radio, and so on. WWV/WWVH also sends machine-readable time codes at 100Hz like this.

jzwinck 13y ago
Indeed--it was more of a hack sixty years ago perhaps. Since then, similar tricks have been used for closed captions, Dolby surround (the original kind), Radio Data System (which puts song names on your car dashboard via FM radio), TV Second Audio Program (listen to shows dubbed in a second language, just press the SAP button on your ancient high-end TV!)....
- jahmed 13y ago
  Wow. I always thought SAP stood for Spanish Audio Program. TIL.
EEGuy 13y ago
>Subcarriers are how they added [...] stereo to FM radio... Set your time machine for 1958, or follow this link [0] to see how RCA did both FM stereo (throughout the article they call it "multiplex") and 67 KHz "SCA" subcarriers. Admire the awesome 5KW FM transmitter cabinetry and transformer shielding. [0] http://fmamradios.com/BTE-10B.html http://fmamradios.com/BTE-10B.html
- jrockway 13y ago
  One thing I find particularly interesting about articles from this time period is that Hz is not yet the name for 1/s, and so everything is in "cycles per second". According to Wikipedia, the transition started in 1960, so we're two years away when this article was published.

the-kenny 13y ago

Quite funny - I know someone who uses a similar setup to send GPS Coordinates for a Quadcopter and a Plane via the audio channel of the video link (he flies the Quadcopter/Plane with video goggles) to the ground station. There, an Arduino controls some stepper motors to point directional antennas at the copter/plane. Project is at https://github.com/KipK/Ghettostation https://github.com/KipK/Ghettostation - video at https://www.youtube.com/watch?v=tiO4YCX7hJo https://www.youtube.com/watch?v=tiO4YCX7hJo - you can hear the modulation in https://www.youtube.com/watch?v=nm0okv8mTsg https://www.youtube.com/watch?v=nm0okv8mTsg

bri3d 13y ago
Cool! I hadn't seen that project before, although I'd seen a few other telemetry-over-audio solutions. They usually use simple FSK just like the "real life" helicopter in the article. Here's an example of a common simple protocol: http://www.flytron.com/pdf/audio_modem.pdf http://www.flytron.com/pdf/audio_modem.pdf

anigbrowl 13y ago

Using spare audio capacity like this is actually very common - prior to digital recording, engineers would dedicate one tape channel to recording a sync signal, and in mission-critical applications would even 'stripe' the tape with the sync signal beforehand (many pro recorders can have recording and read heads active simultaneously).