FELDHELL MACHINE FOR DOS PC
AND CW TRANSMITTER
Feld Hell program for DOS PC and CW transmitter.The difference
The internal timer interrupt of the PC is used to transmit and receive with the correct symbol rate. This timer is also used for the D/A conversion.
IC1A amplifies the audio input signal. IC1B + IC2A are a double phase rectifier. IC2B is a lo pass filter for the detected signals. This signal is amplified by IC3A. The BC547 and IC3B are a simple A/D converter. The time to charge the 10nF capacitor to toggle comparator IC3B is measured by the PC's internal timer.
NOTE: The pins with the text Px refer to the pin numbers of the Centronics plug.
Running the program
Connect the HELL interface to LPT1 via a Centronics printer cable.
For accurate results, your PC should run in DOS mode, not in Windows. Start the program by typing HELL01.EXE. Read the Explanation of the program to find out how everything works.
You can run the program without any hardware. To see how the reception of signals works, activate the replay mode and replay the HELL001.HRX file that you can download as a ZIP file.
Download the software
The interface (there are some extra switches for other experiments)
Inside the box
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