The telegraph code (or, more simply, transmission using Morse code) is still in use. many small beacon devices. The lighthouse is called periodically (most often - once a minute or so) the transmitted signal, which contains the name of the spacecraft (call sign) and the most important telemetry - voltage of the onboard power supply network, condition of batteries and solar batteries, temperature of various points of the device and so on. Accepting these signals, the following tasks can be solved: * give the opportunity to receive a signal “by ear”. Unlike digital signals, which are audibly heard as hissing or buzzing, these signals have a well-recognized, “lively” character. The simple fact of receiving the selected device is usually impressive; since the reception uses only the simplest means, it is the reception of telegraph signals that is primarily used when testing equipment and the first attempts to use it; * demonstrate the Doppler effect. The tone of the signal, due to a change in the relative speed of the device during reception, changes strongly enough so that it can be heard even without musical hearing. This is one of the few experiments available where the Doppler effect is observed directly for electromagnetic waves; * Element of an unordered list to demonstrate the appearance of the device over the horizon, as well as a change in signal strength when it passes over the station; demonstrate the correspondence of the time of these time phenomena calculated on the basis of orbital data using special software.
To receive the telegraph code (also called CW - Continuous wave) the following software is used: * SDR # for receiving a radio signal; * Orbitron for tracking the satellite and taking into account the Doppler effect;
Launch SDR # and select the type of radio: RTL-SDR connected via USB.
In the Radio section, set the switch to USB mode and set the Bandwidth to 5000.
Make sure the “Filter Audio” checkbox is unchecked.
Next, you need to increase the signal gain. To do this, click on the gear.
Move the slider so that the noise level rises by about 10dB.
Launch Orbitron and update TLE first. Click on the tool button.
Press the zipper button to update the TLE.
Click the Download TLE button.
Only the satellites transmitting the telegraph code will appear in the side list on the right. Select the following satellites.
The selected satellites will be shown in the main program window.
Then go to the Calculation tab and click on the Calculation button.
The satellite will automatically calculate the flight time of the satellites. Go to the Rotor / Radio tab and make sure the tracking button is pressed.
In the window with the reception frequency (Dnlink / MHz) the following correct frequency should be set, reduced by 3 kHz, so that the signal is located in the center of the band: