OnAirDecode Tone decoders (CTCSS, DCS, DTMF, selcall) with an SDR
Tone decoders: CTCSS, DCS, DTMF, ZVEI / CCIR / EEA selcall, SELCAL and two-tone pages from FM audio or a sound card.
- Group
- Two-way radio
- In the mode list
- CTCSS, DCS, DTMF, selcall
What Tone decoders (CTCSS, DCS, DTMF, selcall) is
Signalling tones on narrow-FM audio or sound-card audio: CTCSS sub-audible tones (50 tones with the measured frequency), DCS codes (23 bit Golay word, normal and inverted, with the 83-code list), DTMF keys, five-tone sequential calls (ZVEI1, ZVEI2, CCIR, EEA, EIA, DZVEI), aviation SELCAL pairs and a generic two-tone paging detector, with a live tone and spectrum display, a history of everything….
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 CTCSS, DCS, DTMF, selcall.
What OnAir shows
Signalling tones on narrow-FM audio or sound-card audio: CTCSS sub-audible tones (50 tones with the measured frequency), DCS codes (23 bit Golay word, normal and inverted, with the 83-code list), DTMF keys, five-tone sequential calls (ZVEI1, ZVEI2, CCIR, EEA, EIA, DZVEI), aviation SELCAL pairs and a generic two-tone paging detector, with a live tone and spectrum display, a history of everything heard and a squelch-style gate that opens the audio only for a chosen CTCSS tone or DCS code. Receive only.
Limits and what it was checked with
Checked with generated signals and impairments; recordings of real signals welcome.
Which radio you need
Any radio that tunes this range works. An RTL-SDR covers roughly 24 MHz to 1.7 GHz, and every other radio in the radio guide reaches it too. Antenna height and a clear view of the transmitter matter most.
Receiving and the law
Questions about Tone decoders (CTCSS, DCS, DTMF, selcall)
Can I decode Tone decoders (CTCSS, DCS, DTMF, selcall) with an RTL-SDR?
Usually yes for narrowband signals, as an RTL-SDR tunes roughly 24 MHz to 1.7 GHz at up to about 2.4 Msps. Wide signals such as TV channels need a faster radio, and OnAir says next to the source what the selected radio can do.
Is it legal to receive Tone decoders (CTCSS, DCS, DTMF, selcall)?
In many countries it is illegal to intercept or disclose private radio communications. OnAir is a receiver: encrypted calls show up only as encrypted and are never decrypted, and voice needs a library you install yourself. Follow the law where you live.
Can I try Tone decoders (CTCSS, DCS, DTMF, selcall) in OnAir without a radio?
Yes. Most modes include a built-in synthetic test signal, so you can open the screen and try the controls before you own a radio.