Kami menerima dan memecahkan kode transmisi SSTV dari ISS

Hai, Habr.

Seperti yang tertulis dalam pengumuman baru-baru ini , dari 24 hingga 31 Desember, gambar SSTV sedang dikirim dari ISS. Transmisi berada di pita radio amatir pada frekuensi 145.800 MHz dan siapa saja dapat menerimanya.

Mari kita lihat cara kerjanya dan bagaimana sinyal semacam itu dapat diterjemahkan.

Informasi Umum

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.. , . - Orbitron, n2yo.com .

, SSTV . 145.800 , , RTL-SDR V3. 35$ , :

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, , virtal audio card SDR -.

SSTV, 2-3 . , .

:

SSTV , , PD-120 ( ) 0.5. , 1500 , 2300 .

band-pass , :

import scipy.io.wavfile as wav
import scipy.signal as signal
import numpy as np
import matplotlib.pyplot as plt
from PIL import Image


fs, data = wav.read('HDSDR_20201228_075406Z_145803kHz_AF.wav')

def butter_bandpass(lowcut, highcut, fs, order=5):
    nyq = 0.5 * fs
    low = lowcut / nyq
    high = highcut / nyq
    b, a = signal.butter(order, [low, high], btype='band')
    return b, a


def butter_bandpass_filter(data, lowcut, highcut, fs, order=5):
    b, a = butter_bandpass(lowcut, highcut, fs, order=order)
    y = signal.lfilter(b, a, data)
    return y

data1 = butter_bandpass_filter(data, 1400, 2200, fs, order=4)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

. , , :

data_fsk = np.zeros(len(data1))

pos1 = 0
for p in range(0, len(data1)-1):
    if np.sign(data1[p]) != np.sign(data1[p+1]):
        pr = p - pos1
        data_fsk[pos1:p] = np.full(p - pos1, pr)
        pos1 = p
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

"" 2D-:

frame_width = int(0.5*fs) + 203
w, h = frame_width, data_fsk.shape[0]//frame_width
image = Image.new('RGB', (w, h))

data_2d = data_fsk[:w*h].reshape((h,w))
for py in range(h):
    for px in range(w):
        lum = int(data_2d[py][px]*16)
        if lum < 0: lum = 0
        if lum > 255: lum = 255
        image.putpixel((px, py), (lum, lum, lum))
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

:

plt.imshow(image)
plt.show()
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

. 4 . YCrCb, , Y1CrCbY2 - , , . 640480 - 240 , , , 2 .

, 0.5, 240 120, .. 2 . PD-120 .

YCrCb => RGB:

image_rgb = Image.new('RGB', (w//4, 2*h))
for py in range(h):
    for px in range(int(0.125*fs)):
            # PD-120 – 640×480, 190 ?s/pixel
            k = 32
            y0 = 255 - k*data_2d[py][px]
            cr = 255 - k*data_2d[py][px + int(0.1216*fs)]
            cb = 255 - k*data_2d[py][px + 2*int(0.1216*fs)]
            y1 = 255 - k*data_2d[py][px + 3*int(0.1216*fs)]
            image_rgb.putpixel((px, 2*py), (int(y0 + 1.402 * cr), int(y0 - 0.34414 * cb - 0.71414 * cr), int(y0 + 1.772 * cb)))
            image_rgb.putpixel((px, 2*py + 1), (int(y1 + 1.402 * cr), int(y1 - 0.34414 * cb - 0.71414 * cr), int(y1 + 1.772 * cb)))

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

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, SSTV, , :

, . , , 31 ( , ). , Python, SSTV .

ARISS (Amateur Radio on the International Space Station) . , .