Sunday, March 8, 2020

2400 symb/sec bursts with 256 symbol long frames

Interesting PSK-modulated burst signals were picked up recently on a KiwiSDR in the UK:
  • 2400 symb/sec
  • 8-PSK modulation
  • The 1st 6 frames show a substructure of known symbols not present in the following frames

abs(IQ) in 1280 sample frames (12 kHz sampling rate) 


arg(symb) in 256 symbol frames (2400 symb/sec) 






Tuesday, February 18, 2020

2000 symb/sec 8PSK bursts

Today 8PSK bursts with 2000 symb/sec were received on a KiwiSDR in WCNA on 7862 kHz USB (center frequency is 7863.8 kHz).

Starting from the recorded WAV file in I/Q mode, all processing (symbol synchronization, doppler correction, symbol analysis, plotting) was done manually in GNU Octave using signal-analysis for LFSR-detection.

The bursts consist of a BPSK-modulated preamble which is a subsequence of a length-14 LFSR with period 214-1, i.e., a maximal length LFSR. The preamble is followed by 6 720-symbol-long frames, where each frame starts with 72 known 8PSK-modulated symbols, followed by 72 BPSK-modulated unknown symbols and 576 8PSK unknown symbols.

Preamble and frame structure

720 symbol frames

Monday, January 6, 2020

Some HF radar signals

7500 kHz


A number of similar HF radar signals have recently been observed on KiwiSDRs located in Europe on different frequencies.

The pulse repetition rate is 40 Hz (25 ms/pulse).

abs(IQ)

Each pulse consists of a linear chirp and of a pause.

FM demodulation

KiwiSDR TDoA multilateration indicates that these signals come from somewhere in Russia.

KiwiSDR TDoA multilateration

Bursts of what seem to be linear FM chirps have been observed on different frequencies around 8050±~50 kHz.

6390 kHz

Like the signal on 7500 kHz the pulse repetition rate is 40 Hz. However the duty cycle is smaller.

abs(IQ)

FM demodulation


8050 kHz


For this signal, the pulse repetition rate is 96 Hz.

abs(IQ)
Each pulse consists likely of a linear chirp. The spikes in the instantaneous frequency seen below are probably cause by HF propagation effects. Note that these radar-like signals are narrow-band (±1kHz variation in instantaneous frequency, only)

FM demodulation
KiwiSDR TDoA multilateration indicates a position somewhere in the Atlantic Ocean (compatible with the Azores).

KiwiSDR TDoA multilateration