via HACKADAY: This SDR Uses A Tube

When you think of a software defined radio (SDR) setup, maybe you imagine an IC or two, maybe feeding a computer. You probably don’t think of a vacuum tube. [Mirko Pavleski] built a one-tube shortwave SDR using some instructions from [Burkhard Kainka] which are in German, but Google Translate is good enough if you want to duplicate his feat. You can see a video of [Mirko’s] creation, below.

The build was an experiment to see if a tube receiver could be stable enough to receive digital shortwave radio broadcasts. To avoid AC line hum, the radio is battery operated and while the original uses an EL95 tube, [Mirko] used an EF80.

To get the necessary stability, it is important that everything is secured. The original build made sure the tube would not move during operation, although [Mirko’s] tube mounting looks more conventional but still quite secure. Loose coupling of the antenna also contributes to stability, and the tuning adjustments ought to have longer shafts to minimize hand capacitance near the tuning knob. Another builder [Karl Schwab] notes that only about 1/3 of the tuning range is usable, so a reduction gear on the capacitor would also be welcome.

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