Testing the built in IF Filter on the R820T RTL-SDR

As seen in this previous post, the R820T tuner chip used on most RTL-SDR’s has a built in hardware tunable IF filter. Leif, the programmer of the Linrad SDR software has been experimenting with this filter and has uploaded a video of his experiments to YouTube.

In the video he shows how the R820T IF filter can be set to be as narrow as 300 kHz. Using a narrow IF filter can help to reduce the interference from strong nearby stations by up to 30 dB. Leif uses a modified RTL-SDR driver that comes with Linrad which allows the IF filter to be manually modified.

Update: Leif has posted some extra details in the Osmocom mailing list. He writes that the modified driver can be found at https://github.com/dl8aau/librtlsdr and a Windows version is at https://drive.google.com/file/d/0B9m6SAaGpewQeWtyS0lzdW1xVmM/view?usp=sharing.

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