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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:
• #83: Basics of RF Mixe...
Basics of a diode ring mixer:
• #167: How a Diode Ring...
Measurements made on the preselection and IF bandpass filters in an HF upconverter:
• #175: Filter functions...
Ham It Up Upconverter by Opendous, available from NooElec:
code.google.co...
Upconverter by CT1FFU:
www.ct1ffu.com/...
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:
blog.kf7lze.net...
Notes from the video are here:
www.qsl.net/w/w...