![]() 1) It is desirable to provide isolation for audio input and output (typically a 1:1 small audio transformer) to avoid RF feedback or ground loop problems in the audio input and output. FLDIGI does not use the CW Key and FSK unless an external circuit that generates them from the computer audio output is used, but other software does make use of them. Optionally it may provide CW Key Frequency Shift Keying (FSK), and Computer Assisted Transceiver Control (CAT). The radio to computer interface must provide connections for the audio input, audio output, and push to talk (PTT). Microphone or Line In Speaker or Headphone Out Serial Port or USB to Serial Cable Serial Port or USB to Serial Cable Level Converter TxD RxD Level Converter RTS Level Converter DTR RS-232 or TTL Open Collector Open CollectorĬAT Interface PTT Interface CW Key Interface Radio to Computer Interface Hardware The hardware in a digital communications radio system consists of a transceiver, a computer, and an interface. ![]() However, the Soundcard Audio and Push-To-Talk (PTT) control must be configured. It is recommended that you choose an installation folder that is NOT in Program Files or Program Files (86)… For example use: C:\Apps Depending on the version, the actual installation folder might be something like: C:\Apps\Fldigi-3.23.01ĬONFIGURATION FLDIGI can be used WITH or WITHOUT Computer Assisted Transceiver (CAT) Control. INSTALLATION Double click on the download *.EXE file. INTRODUCTION This document describes how to download, install, setup, and use FLDIGI for MARS purposes, specifically MT-63.ĭOWNLOAD Although W1HK, the author of FLDIGI has a WEB page at, the FLDIGI downloads are on SourceForge at: Download the latest version and install. All of the details in this answer are based on reasoning from signal processing theory.FLDIGI MARS Usage FLDIGI MARS Use.docx - 1 16:08 Terry G. (Disclaimer: I have neither used or implemented one. Thus, you can tune a RTTY receiver by changing the receive frequency until the distinct horizontal and vertical ellipses appear. A signal between the two frequencies will appear as a severely off-axis ellipse or a circle (because both filters are passing the signal), and one outside them will appear as an attenuated ellipse. The "crossed" ellipses result from the modulated signal alternating between the mark and space frequencies and thus between the two possible displayed ellipses. The exact shape of the ellipse depends on the phase response of the filters (for example, an ellipse that is perfectly axis-aligned implies a 90° phase shift). The sharper your filters, the narrower the ellipses will be. Since instead filters have roll-off, the signal is merely highly attenuated in the other axis, and an elliptical trace (for an input signal at a single frequency) results. If you had perfect signals and perfect filters, the display would not display ellipses but a straight line on one axis or the other. The simplest accurate way to do it is to keep a buffer of the last however-many filtered samples and draw them as dots ( not lines). (Since you are in the SDR domain:) Do as much as you want to make a nice-looking digital oscilloscope display of that signal.Use the two filters' output signals as the X and Y coordinates of the plot.Pass the incoming signal through two band-pass filters, one at the mark frequency and one at the space frequency.
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