MPDA

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MPDA
Mainmpda.png
Frequencies 53 MHz,1.8 MHz
Frequency Range 1.8 MHz - 53 MHz
Mode USB
Modulation MP‑DASK
ACF —
Emission Designator —
Bandwidth 2 kHz,500 Hz,1000 Hz,1.5 kHz
Location Worldwide
Short Description Experimental Multi‑Parallel Differential Amplitude Shift Keying (MP‑DASK) narrowband data mode for HF/VHF amateur radio text communication, created by amateur radio operator 6L5TNG in the Republic of Korea.
I/Q Raw Recording —
Audio Sample

MPDA (short for Multi-Parallel Differential Amplitude Shift Keying) is a robust, narrowband digital communication protocol designed for amateur radio text transmission over HFHigh Frequency (3-30 MHz) and VHFVery High Frequency (30-300 MHz) bands. Developed by amateur radio operator 6L5TNG (Kang Han) from the Republic of Korea, this protocol specifically utilizes an Intra-Symbol Differential modulation scheme to achieve spectral efficiency and exceptional robustness against fading (QSB).

Technical Overview[edit]

Parameter Specification
Full Name Multi-Parallel Differential Amplitude Shift Keying
Type Digital Data (Text)
Frequency Range HFHigh Frequency (3-30 MHz) (1.8–30 MHzMegaHertz (MHz) 10^6 Hz), VHFVery High Frequency (30-300 MHz)
Location Worldwide (Developed in Republic of Korea)
Audio Range 600 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). – 2200 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). (depending on mode)
Bandwidth ~2000 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).
Sample Rate 44100 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).

Signal Structure[edit]

The MPDA signal employs a unique Intra-Symbol Differential structure to resist fading:

  1. Pilot Tone: A 2200 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). tone precedes the data burst to wake up the receiver and establish AGC/timing lock.
  2. Gap: A fixed silence period (0.15s) separates the pilot and the data burst.
  3. Preamble: Three bytes of 0xAA are sent for bit synchronization.
  4. Payload (Differential Encoding): Each symbol period is split into two halves:
    • First Half (Reference): Fixed amplitude of 0.5. Serves as a local reference for the channel condition.
    • Second Half (Data): Carries the bit information.
      • Logic 1: High Amplitude (1.0) – Louder than reference.
      • Logic 0: Soft-Low Amplitude (0.1) – Quieter than reference.
    • The receiver compares the Data half against the Reference half, allowing correct decoding even if the overall signal strength fluctuates (fading).
  5. Postamble: Three bytes of 0xFF signal the end of transmission (EOTEnd of Transmission).


MPDA Submodes[edit]

MPDA modes are identified by the notation MPDA-<tracks>x<baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second.>.

  • Tracks (Parallel Tones): The number of simultaneous audio carriers transmitting data.
    More tracks = Higher throughput (sending more bits at the same time).
  • BaudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. (Symbol Rate): The modulation speed (how many times per second the signal state changes).
    Lower baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. = Higher robustness against multi-path propagation delays.

Note on Speed: The raw bit rate is calculated as Tracks × Symbol Rate. For example, MPDA-4x10 achieves 40 bpsBits per second (bps) (4 tracks × 10 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second.).

Mode Name Tracks Symbol Rate Raw Bit Rate Notes
MPDA-1x5 1 5 BaudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. 5 bpsBits per second (bps) Very robust, very slow
MPDA-1x10 1 10 BaudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. 10 bpsBits per second (bps) Robust single-track
MPDA-1x15 1 15 BaudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. 15 bpsBits per second (bps) Faster single-track
MPDA-4x5 4 5 BaudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. 20 bpsBits per second (bps) Robust multi-track
MPDA-4x10 4 10 BaudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. 40 bpsBits per second (bps) Default / Reference Mode
MPDA-4x15 4 15 BaudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. 60 bpsBits per second (bps) Fast multi-track
MPDA-8x5 8 5 BaudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. 40 bpsBits per second (bps) Many tracks, low rate
MPDA-8x10 8 10 BaudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. 80 bpsBits per second (bps) High throughput
MPDA-8x15 8 15 BaudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. 120 bpsBits per second (bps) Maximum speed

Unless otherwise noted, MPDA-4x10 is considered the reference mode used in most examples.

Mode Characteristics[edit]

  • Robust Modulation: Uses AFSKAudio Frequency-Shift Keying-based Multi-tone ASKAmplitude-Shift Keying. Unlike traditional FSKFrequency-Shift Keying, MPDA utilizes amplitude states across multiple parallel carriers.
  • Phase Continuity: The transmitter generates Phase-Continuous waveforms to eliminate key clicks and minimize splatter.
  • DSP-Based Demodulation: The receiver utilizes Matched Filter Correlation (Coherent Detection), which offers superior performance in low SNR environments.

Samples[edit]

MPDA 1‑Track Modes
1×5 1×10 1×15
MPDA-1x5.png
MPDA-1x10.png
MPDA-1x15.png

MPDA 4‑Track Modes

4×5 4×10 4×15
MPDA-4x5.png
1MPDA-4x10.png
MPDA-4x15.png

MPDA 8‑Track Modes

8×5 8×10 8×15
MPDA-8x5.png
MPDA-8x10.png
MPDA-8x15.png

Frequencies[edit]

MPDA is designed for use in standard SSBSingle-sideband modulation (USBUpper Side Band Modulation (Radio, referring to reception and modulation mode)Universal Serial Bus (Computer, referring to USB Ports and cables)) voice channels on HFHigh Frequency (3-30 MHz) and VHFVery High Frequency (30-300 MHz) bands. The specific audio frequencies used within the passband are:

  • 1-Track Mode: 1500 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).
  • 4-Track Mode: 800, 1200, 1600, 2000 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).
  • 8-Track Mode: 600, 800, ..., 2000 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). (200 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). spacing)
  • Pilot Tone: 2200 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). (Always used for sync)

Decoding Software[edit]

Currently, there is no standalone application available for end-users. Please refer to the project link below for the source code and usage examples.

The official implementation is provided as a Python library:

  • Core Logic: Encapsulated in mpda_core.py.
  • Transmitter: Generates phase-continuous float32 audio arrays to prevent key clicks.
  • Receiver: Uses matched filters (correlation) to detect symbols even in low SNR conditions.

Project Link[edit]

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