The guys over at SDR for Mariners put together a nice writeup on reducing the electrical interference on the good ol’ cheap RTL-SDR dongle. When the signal you’re looking for is very faint, you need to remove all of unwanted noise or else your signal gets difficult to separate. In their case the unwanted signal is in the form of FM radio.
Even if you aren’t a big RF nerd you know some of these remedies already like ferrite beads (you know those giant blocks on the ends of the expensive cables!). But I’m actually surprised at some of the other ones. I would have thought that the metal connector around a USB cable would help prevent noise, but according to their tests it was acting like a collector for their intrusive FM signal. By removing the shield and just connecting the data pins they dropped the noise by 10db. Not using the extension cable and just plugging straight in is even better.
So the winning combo appears to be all of their methods tested. A stick wrapped in aluminum foil, touching the metal of the USB plug, connected by a USB extension cable, inside a metal housing.
I’d love to see a picture of the final setup. Good tips to know when chasing down a faint signal.