User:Kj6psg/Common VHF UHF Modes

Several common signals are encountered in the USA. These are some examples that should be checked before digging though the list of identified signals to identify an unknown signal.

Trunked Radio

Project 25

C4FMContinuous 4-Level Frequency Modulation

Most single-site P25 Phase 1 systems use C4FMContinuous 4-Level Frequency Modulation modulation for both control and voice channels. C4FMContinuous 4-Level Frequency Modulation reduces the complexity of the transmitter and receiver at the expense of being a less robust modulation than CQPSKContinuous Quadrature Phase-Shift Keying; straight FMFrequency Modulation modulation is used. All C4FMContinuous 4-Level Frequency Modulation operation is Phase 1, and all Phase 1 transmissions (along with all simplex operation, regardless of phase) from mobile/portable radios are C4FMContinuous 4-Level Frequency Modulation.

C4FMContinuous 4-Level Frequency Modulation's advantage is that it is constant-amplitude; a linear final amplifier is not required to produce the modulated signal. As a result, demodulating C4FMContinuous 4-Level Frequency Modulation with an AMAmplitude Modulation detector will not produce any tones.

CQPSKContinuous Quadrature Phase-Shift Keying

Nearly all simulcast Phase 1 systems use CQPSKContinuous Quadrature Phase-Shift Keying due to its resistance to inter-symbol interference due to the propagation delay of different simulcasting sites. CQPSKContinuous Quadrature Phase-Shift Keying modulation is only produced on the output of the trunked system; C4FMContinuous 4-Level Frequency Modulation is used for the input. As CQPSKContinuous Quadrature Phase-Shift Keying is not constant-amplitude, it requires a bulky and expensive linear amplifier to produce the signal; this is why CQPSKContinuous Quadrature Phase-Shift Keying is not found on mobile/portable radios. CQPSKContinuous Quadrature Phase-Shift Keying signals demodulated with an AMAmplitude Modulation detector will produce a strong tone at 4800 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz)., the symbol rate of CQPSKContinuous Quadrature Phase-Shift Keying.

H-DQPSKDifferential Quadrature Phase-Shift Keying

All P25 Phase 2 systems are trunked, and all Phase 2 systems use H-DQPSKDifferential Quadrature Phase-Shift Keying modulation for voice channel outputs (the control channel appears the same as Phase 1, and is usually CQPSKContinuous Quadrature Phase-Shift Keying). It is similar to CQPSKContinuous Quadrature Phase-Shift Keying, but has fewer audible patterns than Phase 1 CQPSKContinuous Quadrature Phase-Shift Keying. Being a QPSKQuadrature Phase-Shift Keying (2 bits per symbol)-based mode, it is not constant amplitude and also requires a linear final amplifier. When demodulated with an AMAmplitude Modulation detector, H-DQPSKDifferential Quadrature Phase-Shift Keying produces a 6 kHzKiloHertz (kHz) 10^3 Hz tone, the symbol rate of H-DQPSKDifferential Quadrature Phase-Shift Keying.

H-DQPSKDifferential Quadrature Phase-Shift Keying is only observed in trunked operation; conventional operation uses P25 Phase 1.

H-CPM

Since mobile/portable units cannot produce the non-linear H-DQPSKDifferential Quadrature Phase-Shift Keying mode but must still support TDMATime Division Multiple Access operation, they use a different modulation called H-CPM. On a spectrogram, it appears similar to single-slot DMR, with a timeslot duration of 30 msmilliseconds (.001 of a second). Unlike DMR, the transmit duration is not perfectly regular, and some variation in packet duration is observed. The Signal Identification Wiki is looking for samples of H-CPM transmissions.

H-CPM is only observed in trunked operation; conventional operation uses P25 Phase 1.

Trunked DMR

MOTOTRBO Connect Plus

Connect Plus systems use a dedicated control channel. Timeslot 1 carries control data, while timeslot 2 can carry voice traffic (otherwise it carries an idle message).

DSDPlus indicates a Connect Plus site in the Event Log status bar as "Con+", and can follow Connect Plus systems. Scanners with DMR trunking support can follow Connect Plus systems.

MOTOTRBO Capacity Plus

Capacity Plus systems use a 'rest channel' in place of a control channel. The most recently active channel in the system becomes the rest channel. Control transmissions on the rest channel are not continuous, but appears as short bursts spaced a few seconds apart. The rest channel changes frequently. Capacity Plus is a newer trunking format and is not supported on XPR6000-series radios.

DSDPlus indicates a Capacity Plus site in the Event Log status bar as "Cap+", and can follow Capacity Plus systems. Scanners with DMR trunking support can follow Capacity Plus systems.

Hytera XPT

Hytera's trunked DMR solution is XPT. DSDPlus indicates a XPT site in the Event log as "XPT", and can follow XPT systems. Scanners with DMR trunking support can follow XPT systems.

NXDN

NXDN is available in two flavors: NXDN48 and NXDN96. Most operation uses NXDN48, which uses a 4.8 kHzKiloHertz (kHz) 10^3 Hz channel bandwidth. NXDN48 is true 6.25 kHzKiloHertz (kHz) 10^3 Hz narrowbanding compliant, and is often found using a 3.125 kHzKiloHertz (kHz) 10^3 Hz channel spacing on the 450-512 MHzMegaHertz (MHz) 10^6 Hz region; a single 12.5 kHzKiloHertz (kHz) 10^3 Hz narrowband channel (of bandwidth +/- 6.25 kHzKiloHertz (kHz) 10^3 Hz) is split in half, producing channel centers at +/- 3.125 kHzKiloHertz (kHz) 10^3 Hz of the original channel center.

DSDPlus will decode NXDN voice and control channels, and follow NXDN trunked systems.

Motorola Type I / II

Motorola Type I and Type II systems (also known as 3600 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. trunking) are dated, but still in use due to their reliability. Voice channels can be identified by their subaudible signalling at 150bps (check for a notch in the AF spectrum at 150 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).). Mobile units transmit a subaudible tone similar to Private Line (PL, or CTCSS), but the tone frequencies are different; this is known as the [i]access tone[/i].

Digital Voice

Motorola trunking systems have the option of using digital voice in place of analog voice with low-rate data. VSELP, P25 CAI (Phase 1 C4FMContinuous 4-Level Frequency Modulation), and Wide-Pulse modulations can be found, although virtually all digital voice systems nowadays use P25 CAI. All three of these modes can also operate in conventional mode.

ASTRO VSELP is an older, Motorola-proprietary vocoder found in the earlier firmwares of ASTRO Saber/Spectra and XTS3000 radios. There is currently no decoder for ASTRO VSELP aside from a properly flashed radio.

P25 CAI is the same C4FMContinuous 4-Level Frequency Modulation found in P25 systems, but using a non-P25 Motorola control channel. Motorola trunking with P25 CAI voice is [u]not[/u] P25 trunking; it is often referred to as IMBE voice to help distinguish it from P25-compliant operation.

Wide-Pulse is a different modulation of ASTRO digital voice, using wideband 4FSK4-Level Frequency Shift Keying instead of narrowband C4FMContinuous 4-Level Frequency Modulation. Both VSELP and IMBE voice can use Wide-Pulse modulation. Wide-Pulse is hard to distinguish by ear with a filtered receiver, but will show no dropoff in the audio spectrum after 2800 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz)..

Harris EDACS

EDACS is an obsolete trunking format that is being superseded by P25. Many EDACS systems are still on the air, despite end of support. EDACS control channels have a distinctive sound. Some EDACS systems support digital voice with the ProVoice format, similar to P25 Phase 1 in the use of the IMBE vocoder. Channel LCNs are index-based; the frequencies must be manually mapped to the LCN.

UniTrunker can decode EDACS control channels, and DSDPlus can decode EDACS ProVoice.

Harris OpenSky

Very few areas use OpenSky due to Harris' failure to produce a system with P25's reliability. Despite its problems, some areas continue to use OpenSky. If you live in an area with OpenSky signals, the Signal Identification Wiki needs I/Q data for OpenSky.

Conventional 2-Way

CTCSS / PL

CTCSS, Continuous Tone Coded Squelch System, is a subaudible tone-squelch system that works by sending a specific tone with analog voice. When the receiver detects both a carrier presence and that specific tone, it unmutes the receiver. Other users of the same frequency will not unmute a CTCSS-enabled receiver as long as the different user groups use different tones.

Motorola calls this Private Line, or PL. Contrary to the name, no additional privacy is afforded by PL use. Instead, the user has the perception of being on a private line as other users of the same frequency do not unmute the user's receiver.

CTCSS changes appearance based on the FFT window size. On smaller window sizes, CTCSS appears wavy. On larger window sizes, CTCSS appears as several peaks spaced apart at the tone's frequency. In both cases, the carrier is no longer a narrow peak, but spread out by 300 to 1000 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).. Typical deviations for CTCSS are 500 to 750 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). for a wideband system and 250 to 375 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). for a narrowband system.

DCS / DPL

DCS works the same as CTCSS, but uses a 23-bit low-rate digital signal at 134.3 bpsBits per second (bps) instead of a single subaudible tone. While DCS is a more robust encoding than CTCSS, it requires sharper filtering that may still cause DCS's warble to bleed through into the audible signal.

Like CTCSS, DCS changes appearance based on FFT window size. On smaller window sizes, the carrier appears to shift between two frequecies. On larger window sizes, DCS appears as two peaks.

P25

P25 Conventional can use either C4FMContinuous 4-Level Frequency Modulation, CQPSKContinuous Quadrature Phase-Shift Keying (repeater outputs), or Wide-Pulse (ASTRO Wideband -- not Project 25 compliant) modulation. See the Trunking section for more information. Some amateur users use P25, but it is uncommon due to equipment costs. Conventional P25 sounds the same as trunked P25 of the same modulation.

NXDN

NXDN can operate in conventional mode in either 4800 or 9600 bandwidths. While most operation is trunked, some conventional repeated or simplex operation can be found in Part 90 and Part 97 spectrum.

D-STAR

D-STAR is a narrowband amateur digital voice mode using GMSKGaussian Minimum-Shift Keying modulation and the AMBE vocoder. D-STAR is only found in amateur spectrum; commercial users use NXDN. D-STAR allows for simple Internet-based linking and encoding of amateur callsigns in the data. D-STAR is easily recognized on a spectrogram due to its rounded power distribution and strong sidebands typical of GMSKGaussian Minimum-Shift Keying.

Yaesu System Fusion

Often called C4FMContinuous 4-Level Frequency Modulation (not to be confused with P25 C4FMContinuous 4-Level Frequency Modulation), this amateur-only mode occupies a wider channel (12.5 kHzKiloHertz (kHz) 10^3 Hz) than D-STAR and has a high data rate with excellent voice quality. System Fusion can also be used for transmitting data between units, such as pictures taken with an attached camera.

DMR

DMR is common on the 70-centimeter band due to equipment availability and ease of linking through the Brandmeister system. Additionally, DMR can be found in simplex mode. Single-slot DMR from a Tier II (dual timeslot capable) or III (trunking capable) radio is turned on and off at a 60 msmilliseconds (.001 of a second) period (30 msmilliseconds (.001 of a second) per timeslot), giving a rapidly pulsed sound upon FMFrequency Modulation or AMAmplitude Modulation demodulation and a very strong ACFAutoCorrelation Function peak at 60 msmilliseconds (.001 of a second).