radio if


Posted on Feb 7, 2014

This is a simple interface box to allow connecting a radio to a PC with some improvements with respect to similar projects available almost everywhere. Interfaces like this one are used to manage via PC the transmission and reception of digital signals (RTTY, BPSK and other digital modes) and of CW (morse) signals (using skimmers to decode them).


radio if
Click here to download the full size of the above Circuit.

I also use this interface to record on the PC my QSOs in particular during contests. A gain control is provided both on the Rx chain and Tx chain to allow to adapt this interface to any kind of radio, providing a constant impedance on the audio lines, on both PC and radio sides. The reson why I realised this board and I did not choose one of those available on the market is mainly for the two above mentioned reasons. Having a goog galvanic isolation between PC and radio is fundamental, to avoid ground-loops which may introduce noise in the receiver and at the same time this will protect both the radio and the PC. Just to make an example, I had a PC sound-card damaged probably by a too high current on its output line (probably the impedance on the radio side was too low). The possibility to adjust the audio levels to fit with the radio and PC is important. In this way I can avoid distorsions that may compromise the transmission and reception, in particular when using AFSK. Obviously, you can buy a digital interface like one of those produced by microHAM. This kind of interfaces will give you much more functionalities, but the category of price is much different and from my point of view, a good PC sound-card works fine (or at least you can get reasonable performances). The connection between the PC and the radio is performed via one serial port which manage the PTT and RTTY/CW signals and via "line in" and "line out" ports...




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