Decoders

Every mode is a channel. This page lists them, says how well each is tested, and covers the modes that need more than a frequency.

Catalog

+ Add lists the modes in the running build, grouped as below.

Fixtures catch decoding bugs but say little about drift, fading, or interference. The fixture library lists where each recording came from. VDL Mode 2, HFDL, Inmarsat Classic Aero and STD-C, DSC and Iridium started as ports of xng. Inmarsat Classic Aero reads the P channel, R/T bursts from aircraft, or a C voice circuit; pick one on the node. Iridium decodes one 50 kHz channel, or bursts across 1 to 10 MHz when you set its span to the radio's sample rate; it reads the middle 80%.

Have a short on-air recording of a fixture-only mode, with the decoded output? It is the most useful contribution there is. See Build and test.

Experimental limits

DAB and DAB+

Wire audio to a Speaker. Auto plays the first audio service. Generation limits the choice to DAB or DAB+. Transmission picks mode I to IV. All run at 2.048 MS/s. Only mode I has been received on air.

A Readout shows the dynamic label and slideshow. The Decoder log keeps received MOT objects with a download link. Files are offered for download, never opened in the interface.

Packet services appear in the same list as audio services. IP services emit datagrams, see IP data.

DVB

DVB-T/T2 and DVB-S/S2 play the chosen programme's first audio and video streams. Wire audio to a Speaker and video to a Video node. Pick a discovered programme or enter its number.

DVB-T/T2: set Standard and Bandwidth. Everything else is read from the signal. Low priority stream picks DVB-T LP. PLP picks a DVB-T2 pipe, or the first TS pipe if left empty. 1.7 MHz fits a 2.048 MS/s radio.

DVB-S/S2: set Symbol rate from 100 kBd to 4 MBd. The channel rate is twice the symbol rate, so a 2 MBd carrier needs a radio that delivers 4 MS/s. Set Roll-off to match the transmitter. DVB-S is always 0.35. DVB-S2 finds the MODCOD on its own, including VL-SNR. Input stream picks one stream on a multistream carrier.

Superframes enables DVB-S2X Annex E formats 0 and 1. Formats 2 to 7 are not supported.

IP data

DAB IP services and DVB-S2 GSE carry IP packets. To put them on your network, wire the channel's events to an Event output, choose Network interface, and set an interface name, address, and prefix. SDR-- creates a TUN interface and writes the packets to it.

Routing and multicast are up to your operating system.

Databases

Wire events to an Event output and choose PostgreSQL or InfluxDB.

PostgreSQL creates the table on first write: one row per event with time, kind, frequency, station, summary, and the full record as jsonb. Add ?sslmode=disable to the URL for a server without TLS.

InfluxDB 2 and 3 take one point per event. The measurement is the event kind, and numbers, flags, and short text from the event become fields.

DMR trunking

Add DMR trunk system, wire Device iq, and enter the control channel in MHz. Pick the system type or leave it on auto. The node creates the DMR channels it needs.

Following runs on the server with no browser open. Voice channels must fit inside the Device's window. A grant outside it is reported.

Record calls keeps finished calls and their audio in memory. Encrypted calls keep only metadata.

SSTV

Tune SSTV to the SSB carrier. A picture takes from 36 seconds to four and a half minutes.

Modes: Robot 36 and 72, Martin M1 and M2, Scottie S1, S2 and DX, PD50 to PD180, Wraase SC2-180.

Wire video to Video to watch a picture arrive. Finished pictures are saved as PNG on the server, even with no client open, and kept for 24 hours, up to 512 pictures.

DECT

The DECT channel surveys base stations: identity, capabilities, and security. It reads signalling only, never call audio.

It needs a radio that reaches 1.9 GHz at 2.304 MS/s or more. HackRF and SDRplay work, RTL-SDR does not.

Carriers are 1.728 MHz apart. European carrier 0 is 1897.344 MHz and the numbers count down. US carriers count up from 1921.536 MHz.

Each record lists the base identity (RFPI), system information, capabilities, advertised and observed security, and handset IDs seen during encryption setup. Encryption is marked active only after a grant is seen. Advertised support does not prove a call was encrypted, and missing signalling does not prove it was not.

ISM sensors

The Sub-GHz channel decodes known sensors and shows raw frames for everything else.

A reading is shown only after its checksum passes. Decoding follows rtl_433 (GPL-2.0-or-later).

Pager text

Some German POCSAG networks send umlauts as { | } [ \ ] ~. SDR-- converts them inside lowercase words only: M}nchen becomes München, Stra~e becomes Straße. [ALARM] and all-caps messages stay as sent.