Thank you to Igor Yatsevich for submitting news about an open source Mini-Whip and Upconverter design that he's created and released for free on GitHub. An upconverter converts HF frequencies into VHF frequencies so that they can be received by RTL-SDRs in their quadrature mode, and a Mini-Whip is a small active antenna for receiving HF signals.
The designs include the PCB Gerber files for manufacturing, the components list and assembly and usage guides. Also both through-hole and SMD designs are provided.
The Mini-Whip design has a frequency range of 10 kHz - 30 MHz and to power it you'll need a 5 - 13V bias tee. You will need to install it up high and preferably away from the house as Mini-Whips are quite susceptible to local noise pickup. Another very important point is that Mini-Whips need to have a good ground connection. The upconverter is based on the ADE-1 mixer, and uses a 125 MHz local oscillator.
Igor's documentation on the project is excellent, and is a good read for getting more information about upconverters and Mini-Whips. He has noted that he is sending us some samples of units that he's built, so when we receive them we'll post again with test results. It looks as if he's put a lot of research into these designs so we're looking forward to seeing how well they work.