R820T tuner support in librtlsdr

Adam Nielsen a.nielsen at shikadi.net
Sat Sep 8 23:29:15 UTC 2012


Hi Steve,

> yesterday I committed code for the Rafael Micro R820T tuner to
> librtlsdr.

That's great!  The code Rafael supply doesn't look very neat, and I haven't 
been able to get a register map out of them either, so great job on getting it 
to work with librtlsdr.

> Sticks with this combination (RTL2832 + R820T) are relatively new on
> the market. The main difference to all the other supported tuners so
> far is that it uses a Low-IF (3.57 MHz) architecture instead of
> Zero-IF. That means the tuner is only connected to the In-Phase ADC
> input, and the internal downconverter of the RTL2832 is generating the
> complex samples. This has the benefit of having no DC offset spike in
> the middle of the spectrum.

If I have read the datasheets correctly, the E4000 is also able to use a 
non-zero IF.  Would doing this help reduce the spike in the middle of the 
spectrum for sticks using the E4000?

> The driver originally had a frequency limitation of 40 MHz to 900 MHz,
> but tests showed that the PLL of my stick can achieve lock up to 1766
> MHz, and indeed both ADS-B at 1090 MHz and L-Band DAB at 1463 MHz, as well as
> GMR at 1556 MHz can be received just fine with the R820T.
> Also, the PLL could lock again at 1850 MHz to 1860 MHz, and the
> reception of a GSM 1800 BTS at 1854 MHz worked as well.

Wow, this sounds like a really good IC!  I might have to go buy one now :-)

Cheers,
Adam.





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