Receiver input reference
Audio, I/Q and remote SDR inputs
Choose the connection that supplies the samples, then the signal family that interprets them. A remote radio can feed the same decoder as a local recording, provided its sample format and bandwidth are suitable.
| Input | Platforms | Connection | Format | Operating notes |
|---|---|---|---|---|
| System audio | iPhone / iPad | Selected microphone or audio input route | PCM audio; a declared complex-I/Q route must satisfy the Mode E format | An ordinary microphone recording does not provide the bandwidth or independent I/Q channels required by DRM+. |
| Core Audio | Mac | Selected physical audio device and channel map | Mono/stereo PCM, or a two-channel I/Q interface | Select the intended input channels and sample rate. Core Audio device support does not turn speaker audio into wideband I/Q. |
| Audio / I/Q file replay | iPhone / iPad / Mac | Local file with the correct signal declaration | Supported audio containers; explicit raw I/Q formats and metadata | PCM is resampled for the decoder. Raw I/Q needs its sample rate, encoding, channel order and centre frequency; do not infer them from the extension. |
| rtl_tcp | iPhone / iPad / Mac | TCP; default port 1234 | RTL0 header, unsigned 8-bit interleaved I,Q | The app's default source rate is 2.048 MS/s. Frequency, gain, correction and offset controls target the remote RTL-SDR tuner. |
| SoapyRemote | iPhone / iPad / Mac | SoapySDR remote service; default port 55132 | CS16 complex samples; UDP by default | Device arguments, antenna, channel, bandwidth, clock and gain must match the server's hardware. It is not an rtl_tcp endpoint. |
| SDR++ server | iPhone / iPad / Mac | SDR++ server protocol; default port 5259 | Signed int8, int16 or float32 I/Q; optional compression | Available radio controls are supplied by the server. A valid connection does not guarantee that every device control is present. |
| Direct USB RTL-SDR | Mac | Local supported RTL-SDR USB device | Complex I/Q from the tuner | The native Mac runtime owns device discovery and access. Direct USB RTL-SDR is not an iPhone/iPad USB feature. |
Decoder-side formats
Analog SSTV and Weather Fax receive normalized 48 kHz mono audio. SSDV can receive normalized 48 kHz audio or 192 kHz complex I/Q, depending on the profile. DRM A-D receive 48 kHz real IF; DRM E receives 192 kHz complex I/Q. These are the decoder-side contracts, not a requirement that every source device run at those exact rates.
Replay metadata matters
For ordinary audio, retain the original container and sample rate. For raw I/Q, record the sample encoding, sample rate, centre frequency and I/Q channel order. A stereo file can contain music, two microphones or I/Q: select the appropriate declaration rather than relying on its channel count.
The DRM samples demonstrate the difference: Modes A-D are 48 kHz mono real IF at 12 kHz, while Mode E is 192 kHz interleaved I,Q in a two-channel WAV. Downmixing Mode E to mono destroys the input representation.
Tuning and bandwidth
Set the RF frequency on the receiver, then use the software offset for small corrections inside the captured passband. The satellite workspace can apply Doppler-aware tuning through a provider that accepts frequency changes. A fixed WAV replay has no hardware tuner to retune.
For HF radiofax on a receiver using the usual USB audio convention, tune 1.9 kHz below the published carrier frequency. Check the station's current instructions and your radio's frequency convention before applying that offset. See Weather Fax tuning and line timing.
Connection checks
- Confirm the actual server type and port. The three remote protocols are not interchangeable.
- Use a source sample rate and bandwidth large enough for the occupied signal.
- Confirm that samples are arriving before changing decoder settings.
- Keep gain below clipping and retain any discontinuity or dropped-sample information with the recording.
- For Mode E, confirm 192 kHz complex I/Q rather than microphone audio.