New R820T Driver with LNA/Mixer/VGA Gain Settings
A few weeks ago we posted about an unreleased modified RTL-SDR driver for SDR# by mm6dos which had controls for the three separate gain stages available in the R820T and some extra controls for controlling software decimation and the IF filter. While that particular driver has not yet been released, a modified driver from randaller, another driver coder has been released. His modified driver enables the LNA/Mixer/VGA gain controls, but does not enable any IF filter or decimation settings.
In the standard R820T driver one of the gain stages is locked to a pre-specified value and the the gain slider is a function of the other two gain values. Having full manual control over all three gain stages may help with optimizing signal SNR levels and reducing noise.
To install the driver simply extract the contents of the zip file from the sourceforge download into the sdrsharp folder. Then open the SDRSharp.exe.Config file in a text editor and add the line
I just discovered that direct sampling mode without hardware modification (see https://www.rtl-sdr.com/rtl-sdr-direct-sampling-mode/) works very well with this new driver for the HF bands.
With the old driver I got only the noise floor and poorly some of the strongest stations.
With the new one and still keeping the normal antenna connection, here is what I caught for the 12 Mhz broadcast band: http://exvacuo.free.fr/div/Radio/SDR/RTL2832U.jpg
The antenna is a long wire. I can receive in very good conditions any frequency between 5 and 30 Mhz. Below 5 Mhz, the signal is weakened. It doesn’t allow for MW/LW reception. Beyond 12 Mhz, the oscillateur of the RTL starts up. This adds some noise from the VHF spectrum. Nevertheless by adjusting the lna/mixer/vga gains, excellent reception is possible from 12 to 30 Mhz.
I have 2 RTL2832U keys. There is differences in the results. The best one for this purpose is the smallest : http://exvacuo.free.fr/div/Radio/SDR/RTL2832U.jpg.
My 3rd key is a RTL2832P. It doesn’t works well with this driver for direct sampling and there is a more general problem in setting frequencies (the FM band appears near “40 Mhz”).
Sorry, I put twice the same link.
Here is the spectrum of the 12 Mhz band:
http://exvacuo.free.fr/div/Radio/SDR/RTL2832U%2Bdriver3gains-12Mhz.jpg
What means “VGA” gain? When low, the spectrum is clear but the S/N bad, and vice versa.
Nevertheless with this driver it’s possible to improve the S/B by 5 dB and/or to reduce the unwanted signals in the spectrum (mainly thanks to the VGA gain). The LNA gain can be set near maximum.
Unfortunately this driver doesn’t work with the new RTL2832P key (for DVB-T2) while the old one still works. Each cursor “works” in that it normally acts onto the noise floor, but surprisingly, there is absolutely no useful signal.
I assume that “VGA” (“variable gain amplifier”?) refers to the amplifier at the output of the R820T tuner chip; see the R820T datasheet.
David, you have to play with the sliders until the signal suite your needs.
There is no default setting as everybody’s antenna gain is different.
Is there any information about how to set the three sliders properly?
Does anybody know if the New R820T Driver with LNA/Mixer/VGA Gain Settings work with the hdsdr software ?????????????????