Constellation Diagram Analyser

Fifteen modulation formats. BPSK, QPSK, and 8 PSK from the PSK family. Pi over 4 DQPSK and pi over 8 D8PSK from the differential PSK family, rendered as the 8 and 16 point visible symbol unions. 2FSK and 4FSK rendered in the deviation domain. 16 QAM, 64 QAM, 256 QAM, 1024 QAM, and 4096 QAM from the rectangular QAM family, plus the 32, 128, and 512 QAM cross constellations rendered correctly as square grids with the corner blocks removed (6 by 6 minus 1 by 1 corners, 12 by 12 minus 2 by 2, 24 by 24 minus 4 by 4) — the formats point to point microwave backhaul radios actually run. Ideal points are rendered in red and received impaired symbols in blue throughout.

Yes. Pi over 4 DQPSK is the TETRA voice plus data waveform (ETSI EN 300 392-2, 18 ksym per second, root raised cosine rolloff 0.35), pi over 8 D8PSK is the TETRA TEDS phase modulation, and 4FSK covers DMR (ETSI TS 102 361-1), P25 Phase 1 C4FM (TIA 102), and NXDN, all at 4.8 ksym per second. 2FSK covers POCSAG paging, MPT 1327 FFSK control channels, and RTTY. FSK formats are rendered in the deviation domain (deviation levels at plus or minus one third and plus or minus full deviation for 4FSK) as land mobile radio test sets display them, and their EVM corresponds to the FSK error or modulation fidelity figure those test sets report. Because an FM transmitter has no IQ modulator, the linear modulator impairments (IQ imbalance, DC offset, carrier phase, AM AM and AM PM, CFO rotation) are disabled for FSK formats — AWGN and phase noise act on the deviation trajectory. Compliance rows cover the TETRA 10 per cent RMS vector error limit and the P25 Class A 5 per cent modulation fidelity limit. ETSI publishes deviation tolerances rather than an EVM style limit for DMR, so no invented DMR limit is shown. Dedicated TETRA, DMR, and P25 C4FM presets load the correct symbol rate, rolloff, and band.

HF serial tone modems (MIL-STD-188-110, STANAG 4285, STANAG 4539) transmit PSK and QAM constellations that are already covered: 8 PSK for the classic 2400 symbol per second serial tone waveforms and 16 QAM through 256 QAM for the wideband appendices. The HF Modem preset loads serial tone 8 PSK at 2.4 ksym per second with HF representative noise and phase jitter. RTTY and SITOR are 2FSK, also covered. ALE (MIL-STD-188-141 8 tone FSK) and FT8 style waveforms are orthogonal multi tone signalling with no IQ symbol constellation to display — they are measured on a spectrum view, so they belong in the FFT Spectrum Analyser rather than a constellation tool, and no invented constellation rendering is offered for them.

Nine impairments are applied in a physically motivated cascade matching the hardware signal flow. AM AM radial compression first (from the power amplifier). Then AM PM phase rotation. OFDM PAPR clipping in OFDM mode. IQ amplitude imbalance from the modulator. IQ phase imbalance. Carrier phase rotation. DC offset on each axis. Per symbol phase noise from the local oscillator. AWGN from the receive chain. Each impairment can be enabled or disabled independently so the visual signature of each one can be studied in isolation.

Per source EVM contributions are computed and surfaced as a percentage of total EVM power. The diagnosis engine identifies the dominant contributor and maps it to the recognisable visual pattern. Phase noise produces arc shaped elongation. IQ phase imbalance produces a skewed grid. AM AM produces compressed outer corners. AM PM produces rotated outer symbols. DC offset produces a shifted centre. The matched pattern and a recommended corrective action are surfaced together.

Carrier frequency offset is specified in Hz or ppm and converted to a phase increment per symbol delta phi equals 2 pi times f CFO divided by f sym. Each rendered symbol accumulates the phase increment, producing the characteristic arc or ring pattern of uncompensated frequency offset. In OFDM mode, ICI EVM is modelled as pi times magnitude of epsilon divided by square root of 3 times 100 per cent, where epsilon equals f CFO divided by subcarrier spacing.

A separate eye diagram panel generates 600 random symbols at the selected modulation order, upsamples at 8 times the symbol rate, applies a raised cosine matched filter with configurable rolloff alpha (0.01 to 0.99), and adds AWGN at sigma equal to EVM divided by 100. The filtered waveform is chopped into 2 symbol period windows and 200 traces are overlaid to produce the canonical eye diagram. I or Q channel selectable. Useful for assessing timing margin, noise margin, and inter symbol interference alongside the constellation view.

BER is estimated using the Gray coded Q function for PSK and QAM. PSK BER is approximately 2 over k times Q of (square root of 2 Es over N0) times sin of (pi over M). QAM BER is approximately 4 over k times (1 minus 1 over square root of M) times Q of (square root of 3 Es over N0 over (M minus 1)). These are the standard approximations used across the industry for AWGN performance estimation.

The EVM Calculator focuses on quantitative EVM with budget allocation and standards compliance. The Constellation Diagram Analyser provides the visual view that shows what each impairment looks like and automatically diagnoses the dominant one. The FFT Spectrum Analyser shows the frequency domain signature alongside. Use the EVM Calculator for budget allocation. Use the Constellation Diagram Analyser to visualise and diagnose impairments. Use the FFT Spectrum Analyser to confirm spectral signature.

No. The analyser runs entirely in your browser. No constellation data, impairment configurations, or design parameters are submitted to a server. Useful for commercially confidential transmitter and receiver design work, defence and intelligence radio development, and environments where information security policy prohibits sending engineering data to third party services.