Leif, the programmer of Linrad has recently uploaded a video to YouTube showing how he shields his RTL-SDR dongles to prevent the USB shield from acting as an antenna and picking up unwanted signals. In the video he also measures how well various other SDRs are at avoiding USB shield interference.
From the video we can see that Leif’s shielding method uses the following steps:
- The metal box is RF tight and held together by many screws.
- The USB shield and external antenna connector shields are both connected to the box.
- The USB 5V line is decoupled to the GND line.
- The USB 5V line has a ferrite on it.
- The internal coax connection between the external connector and RTL-SDR antenna connection has a ferrite on it.
- The USB cable has a ferrite where it enters the box.
With this shielding effort the interference is significantly reduced.