Decode ROS (HF) with an SDR

Group

Amateur: digital

In the mode list

HF weak-signal chat, 4/8/16 baud

What ROS (HF) is

ROS weak-signal HF chat mode (detector, text decoding partial): the sideband audio goes to a waterfall, and every 2 s the last 16 s are measured for the publicly described ROS physical layer, one tone at a time on a fine grid (about 144 tones, 15.6 Hz apart), about 2.25 kHz wide, 4 / 8 / 16 baud. A detection names the sub-mode (ROS 4 / 8 / 16 baud), the tone range and the grid, and marks the….

Frequencies and settings

OnAir takes any frequency you type; the numbers above are the mode's starting point and the range its table describes. In the app the shortcut label is HF weak-signal chat, 4/8/16 baud.

What OnAir shows

ROS weak-signal HF chat mode (detector, text decoding partial): the sideband audio goes to a waterfall, and every 2 s the last 16 s are measured for the publicly described ROS physical layer, one tone at a time on a fine grid (about 144 tones, 15.6 Hz apart), about 2.25 kHz wide, 4 / 8 / 16 baud. A detection names the sub-mode (ROS 4 / 8 / 16 baud), the tone range and the grid, and marks the band on the waterfall. The text is NOT decoded: the framing, coding and FEC of ROS are not published (partial, needs a public spec); use the ROS program to read it.

Limits and what it was checked with

Checked with generated signals and impairments; recordings of real signals welcome.

Which radio you need

This is a shortwave mode, so the radio has to tune HF. An SDRplay, Airspy HF+ or an RTL-SDR in direct-sampling mode do that directly; with a HackRF an HF upconverter or a direct-sampling receiver is the usual route. A long wire or loop antenna matters more than the radio.

Receiving and the law

Questions about ROS (HF)

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