Thank you to Mitsonobu Saitou for writing in and sharing with us a product that he has created which improves the sensitivity of the Malachite DSP software defined radio and other shortwave radios by up to 20dB by improving the grounding. It appears to work by using the negative USB line as a ground via a modified USB cable with grounding clip on the other end. The product is available via Amazon Japan with international shipping.
The Malachite DSP is a portable battery powered software defined radio with built in screen. It is popular amongst shortwave listeners.
Saitou writes the following summary, and full details about the product are available on his blog (link uses Google Translate to translate from Japanese to English):
Today's item is "Dokodemo Earth KUN". This is an item to pull the ground wire from the charging connector of DCL radios and Mlachite DSPs.
The sensitivity of the receiver will be improved by strengthening the grounding. This is how I applied it.
It is easy to connect by pulling out the ground wire from the charging connector instead of the antenna jack.
It can also be used as a loop antenna by connecting the ground to the antenna.
We have confirmed the effectiveness of this product outdoors. Users who have used this item have experienced a significant increase in sensitivity.