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I created a Python block that takes five user inputs and generates a .txt file containing timestamps in column 1 and Doppler shift data in column 2 based on the entries.

The first two inputs are two-line elements, the third is the frequency of a CubeSat, the fourth is a timestamp and the last one specifies the file destination where the .txt file will be stored, similar to the "File Sink" block.

For example, in the default "File Sink" block of GNU Radio, clicking on the three dots opens a window to browse and select the final file destination. However, I haven't been able to replicate this behavior in my code.

Additionally, is it possible to run this block before the entire flowgraph starts when clicking "Execute the flowgraph"?

Example: Step 1. Entry 1: "1 49263U 21088D 24308.92471420 .00079255 00000+0 26750-2 0 9998"

Entry 2: "2 49263 97.4796 14.7363 0010511 313.1417 46.8944 15.30328253170926"

Entry 3: 437.250e6

Entry 4: 1730713098

Entry 5: ---click on three dots to open file browser to save file---

Step 2. Click on "Execute the flowgraph" ---runs the python block before main flowgraph---

import scipy.constants
import skyfield.api
from skyfield.api import wgs84, EarthSatellite
import numpy as np
import datetime
from tkinter import filedialog
import tkinter as tk
from gnuradio import gr

class DopplerBlock(gr.sync_block):
  
    
    def __init__(self, tle_line1='', tle_line2='', frequency=0, timestamp=0):
        gr.sync_block.__init__(
            self,
            name='Doppler Shift Generator',
            in_sig=None,
            out_sig=None
        )
        
        self.tle_line1 = tle_line1
        self.tle_line2 = tle_line2
        self.frequency = frequency
        self.timestamp = timestamp  # User-provided timestamp
        self.ts = skyfield.api.load.timescale()
        self.groundstation = wgs84.latlon(53.1111, 8.8583, 0)  # ESTEC ground station
        self.output_file_path = self.get_file_path()

    def get_file_path(self):
        """Opens a file dialog to let the user choose a file."""
        root = tk.Tk()
        root.withdraw()  # Hide the root window
        file_path = filedialog.asksaveasfilename(title="Select file to save data")
        return file_path if file_path else None

    def compute_doppler(self):
        if not self.tle_line1 or not self.tle_line2:
            raise RuntimeError("Both TLE lines must be provided.")
        
        satellite = EarthSatellite(self.tle_line1, self.tle_line2, 'satellite', self.ts)
        
        unix_epoch = datetime.datetime(1970, 1, 1, tzinfo=datetime.timezone.utc)
        t0 = unix_epoch + datetime.timedelta(seconds=self.timestamp)
        t0 = self.ts.from_datetime(t0)

        # Generate time steps
        duration_s = 25 * 60  # 25 minutes in seconds
        time_steps = np.arange(0, duration_s, 0.1)  # Every 0.1 sec
        t = t0 + time_steps / (24 * 3600)  # Convert seconds to fractional days
        
        # Compute Doppler shift
        topocentric = satellite.at(t).observe(self.groundstation)
        _, _, range_rate = topocentric.apparent().velocity.km_per_s
        range_rate *= 1e3  # Convert to m/s

        doppler_shift = -range_rate / scipy.constants.c * self.frequency

        # Save to file if path is provided
        if self.output_file_path:
            with open(self.output_file_path, 'w') as output_file:
                for time, shift in zip(time_steps, doppler_shift):
                    output_file.write(f'{self.timestamp + time}\t{shift}\n')

    def work(self, input_items, output_items):
        """This block does not process streaming signals, so work does nothing."""
        return 0

I created a Python block that takes five user inputs and generates a .txt file containing timestamps in column 1 and Doppler shift data in column 2 based on the entries.

The first two inputs are two-line elements, the third is the frequency of a CubeSat, the fourth is a timestamp and the last one specifies the file destination where the .txt file will be stored, similar to the "File Sink" block.

For example, in the default "File Sink" block of GNU Radio, clicking on the three dots opens a window to browse and select the final file destination. However, I haven't been able to replicate this behavior in my code.

Additionally, is it possible to run this block before the entire flowgraph starts when clicking "Execute the flowgraph"?

Example: Step 1. Entry 1: "1 49263U 21088D 24308.92471420 .00079255 00000+0 26750-2 0 9998"

Entry 2: "2 49263 97.4796 14.7363 0010511 313.1417 46.8944 15.30328253170926"

Entry 3: 437.250e6

Entry 4: 1730713098

Entry 5: ---click on three dots to open file browser to save file---

Step 2. Click on "Execute the flowgraph" ---runs the python block before main flowgraph---

import scipy.constants
import skyfield.api
from skyfield.api import wgs84, EarthSatellite
import numpy as np
import datetime
from tkinter import filedialog
import tkinter as tk
from gnuradio import gr

class DopplerBlock(gr.sync_block):
  
    
    def __init__(self, tle_line1='', tle_line2='', frequency=0, timestamp=0):
        gr.sync_block.__init__(
            self,
            name='Doppler Shift Generator',
            in_sig=None,
            out_sig=None
        )
        
        self.tle_line1 = tle_line1
        self.tle_line2 = tle_line2
        self.frequency = frequency
        self.timestamp = timestamp  # User-provided timestamp
        self.ts = skyfield.api.load.timescale()
        self.groundstation = wgs84.latlon(53.1111, 8.8583, 0)  # ESTEC ground station
        self.output_file_path = self.get_file_path()

    def get_file_path(self):
        """Opens a file dialog to let the user choose a file."""
        root = tk.Tk()
        root.withdraw()  # Hide the root window
        file_path = filedialog.asksaveasfilename(title="Select file to save data")
        return file_path if file_path else None

    def compute_doppler(self):
        if not self.tle_line1 or not self.tle_line2:
            raise RuntimeError("Both TLE lines must be provided.")
        
        satellite = EarthSatellite(self.tle_line1, self.tle_line2, 'satellite', self.ts)
        
        unix_epoch = datetime.datetime(1970, 1, 1, tzinfo=datetime.timezone.utc)
        t0 = unix_epoch + datetime.timedelta(seconds=self.timestamp)
        t0 = self.ts.from_datetime(t0)

        # Generate time steps
        duration_s = 25 * 60  # 25 minutes in seconds
        time_steps = np.arange(0, duration_s, 0.1)  # Every 0.1 sec
        t = t0 + time_steps / (24 * 3600)  # Convert seconds to fractional days
        
        # Compute Doppler shift
        topocentric = satellite.at(t).observe(self.groundstation)
        _, _, range_rate = topocentric.apparent().velocity.km_per_s
        range_rate *= 1e3  # Convert to m/s

        doppler_shift = -range_rate / scipy.constants.c * self.frequency

        # Save to file if path is provided
        if self.output_file_path:
            with open(self.output_file_path, 'w') as output_file:
                for time, shift in zip(time_steps, doppler_shift):
                    output_file.write(f'{self.timestamp + time}\t{shift}\n')

    def work(self, input_items, output_items):
        """This block does not process streaming signals, so work does nothing."""
        return 0

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2 Answers 2

Sorted by: Reset to default 1

That's not behaviour of your python code, but specified in the block-defining YAML file; tutorial explaining that. If you haven't already, it would be worth to go through the tutorials on https://tutorials.gnuradio. from "What is GNU Radio" to "Creating an OOT (Python block example)" in linear order; we wrote all that with users like you in mind :)

You can find the File Sink's "Block definition" YAML file linked from the bottom of its Block documentation page; look for dtype: in the first element of parameters:.

I think I mentioned this before, but you most definitely do not want an actual subclass of gr.block if you're not doing signal processing. And, again, no graphical user interface creation in your own blocks :)

To run a python code before start, an easy way is to use Python Snippet block in GNU radio. Select section of Flow graph to After Init or After Start as required. Put the code to Code Snippethttps://wiki.gnuradio./index.php/Python_Snippet

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