Glossary
Key terms and abbreviations used throughout this documentation.
Signal & RF
AGC — Automatic Gain Control
Hardware circuit that adjusts receiver sensitivity automatically to compensate for varying signal levels and prevent overload on strong signals.
De-emphasis
Frequency correction applied during FM decoding to undo the treble boost added before broadcast. Must match the regional standard: 50 µs in Europe and Asia, 75 µs in the Americas. A mismatch causes incorrect audio level measurements.
FM — Frequency Modulation
The broadcast standard MultiTuner monitors. Signals occupy the 64–108 MHz band and carry stereo audio, RDS data, and optionally SCA subcarriers.
IF — Intermediate Frequency
The internally down-converted signal frequency at which the receiver performs filtering and demodulation.
LNA — Low-Noise Amplifier
The first gain stage in the RF chain. Higher LNA gain improves sensitivity on weak signals but increases the risk of overload on strong ones.
Multipath
Interference caused by the FM signal arriving via multiple reflected paths simultaneously. Measured as a percentage (0–100%); high values indicate reflections from buildings or terrain that distort the signal.
Pilot
The 19 kHz stereo pilot tone embedded in FM stereo broadcasts. Its presence confirms a stereo signal; absence means the station is broadcasting in mono.
RF — Radio Frequency
The raw antenna signal before the receiver demodulates it. MultiTuner receives this via the rear-panel antenna input.
RSSI — Received Signal Strength Indicator
Measures how strong the antenna signal is. Low RSSI means a weak or distant transmitter; too-low RSSI triggers a signal alarm.
SCA — Subsidiary Communications Authority
An FM subcarrier used for auxiliary services (background music, paging) alongside the main broadcast. Not decoded by MultiTuner but present in the RF spectrum.
SNR — Signal-to-Noise Ratio
Measures how cleanly the FM signal stands above background noise. Expressed in dB; values below ~20 dB typically cause audible degradation.
Stereo Blend
The degree of stereo separation applied by the FM decoder. Automatically reduces toward mono as SNR drops, trading stereo width for lower noise.
VHF — Very High Frequency
The spectrum band (30–300 MHz) that contains the FM broadcast range. MultiTuner operates within the 64–108 MHz portion of this band.
RDS
AF — Alternative Frequencies
List of other frequencies broadcasting the same programme, used by receivers to switch automatically when signal quality drops.
EON — Enhanced Other Networks
RDS feature that cross-references programme and traffic information from other stations in the same network.
PI — Programme Identification
A unique 4-character hex code that identifies a station in the RDS system, independent of frequency or name.
PS — Programme Service
The 8-character station name transmitted via RDS. This is what appears on car radio and receiver displays.
PTY — Programme Type
A numeric RDS genre code that classifies the station's content (e.g. News, Rock, Classical).
RBDS — Radio Broadcast Data System
The North American variant of RDS, functionally similar but with different PTY code assignments.
RDS — Radio Data System
A digital subcarrier embedded in FM broadcasts carrying station metadata: name, free text, programme type, and more. MultiTuner decodes and displays RDS data per channel.
RT — RadioText
A free-text message broadcast by the station via RDS, up to 64 characters. Typically used for current song title, programme info, or promotions.
TA — Traffic Announcement
RDS flag set by the station during an active traffic bulletin.
TP — Traffic Programme
RDS flag indicating the station regularly carries traffic announcements.
IP Streaming
HLS — HTTP Live Streaming
An alternative streaming format served by MultiTuner at /api/tuner/{id}/live.m3u8. Audio is split into short HTTP file segments; open the .m3u8 URL in VLC or any HLS-compatible player for instant playback without UDP configuration.
IGMPv2 — Internet Group Management Protocol v2
The multicast group protocol MultiTuner uses when streaming to a multicast address. Network switches use IGMP reports to forward the stream only to ports with active receivers, avoiding unnecessary broadcast traffic.
IGMPv3 — Internet Group Management Protocol v3
Extends IGMPv2 with Source-Specific Multicast support. Allows a receiver to request a multicast group only from a specific source IP, improving control in managed network environments.
MPEG-TS — MPEG Transport Stream
The container format MultiTuner uses for IP streaming. Audio is multiplexed into fixed-size transport packets and sent over UDP to the configured destination address and port.
SSM — Source-Specific Multicast
A multicast mode supported via IGMPv3 where receivers subscribe to a specific (source, group) pair rather than just a group address. Prevents unwanted reception of streams from other sources on the same multicast address.
UDP — User Datagram Protocol
The transport layer used for MPEG-TS streaming. Connectionless and low-latency, with no delivery guarantee — suitable for live audio where a lost packet is preferable to buffering delay.
XSPF — XML Shareable Playlist Format
The playlist format returned by GET /api/playlist. Contains stream URLs for all active channels; open in VLC, foobar2000, or any XSPF-compatible player to access all streams at once.
API & System
Bearer token
The HTTP authentication scheme used by the MultiTuner API. Obtain a token via POST /api/login and pass it in the Authorization header of subsequent requests.
JSON — JavaScript Object Notation
The data format used for all MultiTuner API request and response bodies.
JWT — JSON Web Token
The format of the session token returned by POST /api/login. Must be included as Authorization: Bearer <token> in every authenticated API request.
MIB — Management Information Base
The file that describes MultiTuner's SNMP object tree. Load it into your SNMP monitoring platform to enable device-specific queries and traps. Download from GET /api/mib.
NVRAM — Non-Volatile RAM
The memory where MultiTuner stores its configuration. All settings — channel frequencies, thresholds, network config — survive power cycles without a battery.
NTP — Network Time Protocol
Used by MultiTuner to keep its clock synchronized with a time server. Accurate system time is important for correct alert timestamps and log entries.
REST — Representational State Transfer
The architectural style of the MultiTuner HTTP API. All web interface actions are also available programmatically via REST endpoints.
RMS — Root Mean Square
The measurement method used for audio levels in MultiTuner. Reflects effective (perceived) signal loudness rather than instantaneous peak values, making it a better indicator of silence or overload conditions.
rsyslog
A standard Unix logging daemon. MultiTuner can forward its internal log stream to an external rsyslog server, enabling centralized log collection alongside other infrastructure components.
SNMP — Simple Network Management Protocol
Network management protocol supported by MultiTuner. Download the MIB file from GET /api/mib and load it into your SNMP manager to monitor the device alongside other network equipment.
SWU — SWUpdate package
The signed firmware bundle format accepted by POST /api/system/upgrade. Only packages signed with the MultiTuner key are installed; unsigned files are rejected.
Physical & Connectors
1U
One rack unit — 44.45 mm of vertical space in a 19" rack. MultiTuner occupies a single 1U slot.
BNC — Bayonet Neill–Concelman connector
One of the antenna connector variants available on MultiTuner depending on order configuration.
IEC C14
The power inlet connector on the MultiTuner rear panel, accepting a standard C13 power cord (the same type used by most servers and switches).
RCA — phono connector
Used for the MultiTuner audio monitoring output (0 dB, 600 Ω).
RJ-45
8P8C Ethernet connector — the single network port on the MultiTuner rear panel, shared between management traffic and UDP streaming output.
Units
| Symbol | Name | Usage in MultiTuner |
|---|---|---|
| dB | Decibel | SNR, channel selectivity, audio separation, AM suppression |
| dBm | Decibel-milliwatts | RF signal power relative to 1 mW into 75 Ω |
| MHz | Megahertz | FM frequencies as displayed in the web interface |
| kHz | Kilohertz | FM frequencies as expressed in the API (e.g. 104300 = 104.3 MHz) |
| µs | Microsecond | De-emphasis time constant: 50 µs or 75 µs |
| µV | Microvolt | RF sensitivity — MultiTuner achieves 26 dB SNR at 3.5 µV input |