This video shows how a mixer can be used to upconvert the HF frequency band into a higher frequency IF (intermediate frequency) so that the RTL-SDR can be used to receive/listen. A homemade double-balanced diode ring mixer is shown here, but something like the inexpensive ADE-1 from Mini Circuits would work very well also. Higher performance operation (less interference, intermodulation distortion, etc.) can be achieved by utilizing pre-selection filtering in the RF path, and IF (intermediate frequency) bandpass filtering between the mixer IF output and RTL-SDR input. The controls to automatically remove the IF offset from the display, and to control the RTL-SDR tuner and demodulator gain from within HDSDR is also shown. Some 40m SSB/LSB signals, and some AM shortwave broadcast signals are listened to as examples. Here are a few relevant links:
Video on basics of mixers and frequency translation:
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Basics of a diode ring mixer:
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Measurements made on the preselection and IF bandpass filters in an HF upconverter:
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Ham It Up Upconverter by Opendous, available from NooElec:
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Upconverter by CT1FFU:
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There is also an NE602 based upconverter featured in the January 2013 issue of QST magazine.
Here's a nice summary of 18 upconverters in a blog by KF7LZE in Sept 2014:
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Notes from the video are here:
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