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rtlsdr emulator: Running rtlsdr-based software with an SDRplay device

There is no doubt that the (various) SDRplay RSP devices are technically superior to the common RTLSDR "dab" sticks. That being said, there is also no doubt that there is much more software written - and made available - for the RTLSDR sticks than for the SDRplay devices.

After adding SDRplay support to some rtlsdr-based software packages, i.e. dump1090 and acarsdec, it was felt that rewriting each piece of rtlsdr based software for SDRplay support was hardly an ideal approach.


Therefore an other approach was taken: create a library that shows itself as an RTLSDR library, and internally translates calls to appropriate calls to the SDRplay libary, bridging the gap between the API of the SDRplay devices.

Of course it is required to have the dll (or shared lib) for the SDRplay device installed, after all, that is the one doing the work. The fake rtlsdr library (librtlsdr.so, or rtlsdr.dll, or librtlsdr.dll as it should be named for some windows executables) is merely a translator from commands to the rtlsdr api to commands to the SDRplay api.


Version of october 2019

The version now resulted from a significant simplification, following the observation that not in all cases the "async" function was executed in a separate thread.


Use under Windows (or how to run sdr# with the SDRplay)

Mapping the gain setting as used on an RTLSDR 2832 based stick to the more elaborate settings for SDRplay was found to be unsatisfactory. A decent balance has to be found between selecting the gain reduction in the LNA (by choosing an lna state) and the if Gain reduction.

Therefore, for Windows an alternative solution is being developed: under Windows the gain setting to the stick - as often done in the program - is cut short and instead, the user controls gain through a small dialog box shows that allows the precise setting for the lna state, Gainreduction and agc.

rtlsdr emulator

The picture shows - top left - a small dialog box "owned" by the rtlsdr.dll file that allows a precise setting of the lna state and the gain reduction. The small checkbox in the dialog window is for controlling the setting of the AGC.

On the right one sees the original widget for the rtlsdr software, note that gain setting in this latter widget has no effect, gain setting is controlled by the SDRplay gain setting widget.


Installing under Windows

Although it is quite well possible to build a dll file, the repository contains one, together with the other dll's needed to run the emulator.

As an example, to run sdr# with the SDRplay, all dll's from the example folder which is part of the repository, are copied into the directory (folder) of the SDR#, with the result as shown above.


Use under Linux

For Linux the gain setting as set by the user is translated in a setting for the LNA and one for the if gain reduction. The "algorithm" is that first the gain is translated into a gain reduction and the LNA is made "responsible" for one third of this, the other part to be delivered by the if gain reduction.

Therefore, under Linux, using the emulator is completely transparant.

rtlsdr emulator


Installing under Linux

For Linux one - obviously - can create a shared library (see below). However, the repository contains a precompiled librtlsdr.so file, that can be placed in e.g. /usr/local/lib


Building a library file

For use under Windows, a precompiled version of the dll is available. Best is to look at the example program, that contains all dll's necessary to run the emulated dll driver.

The repository contains two makefiles, one for Linux and one for (cross) compilation for Windows. Note that the sources contain some compiler directives #ifdef MINGW32 to separate the code sections for the windows version from the sections for the Linux version.

The "librtlsdr.so" file in the repository was made under Fedora The "rtlsdr.dll" file in the respository was made under Fedora, using the Mingw64 32bits resource and C compilers.


Issues

There are quite some differences between the two API's, so there is not a 100% match. However, since in most cases only a subset of the rtlsdr API is used, it turns out that programs like acarsdec, dump1090, rtl_433, aiswatcher, dump978 run pretty well with the emulator.

An issue is that the range of samplerate between the devices differs, while RTLSDR based sticks support a range of 960 KHz .. 2.5 MHz, the SDRplay supports 2 Mhz and up to 8 (or 10) Mhz. Samplesrates for the RTLSDR stick between 1 and 2 MHz are handled by the emulerator using the double of this rate and decimating with a factor of 2.

The Windows version is still slightly experimental - for me (being a Unix/Linux person for the last 45 years) it is the very first program using a windows API directly - and it is most likely that some changes will be applied.


Copyrights

This software:

  • Copyright (C) 2018, 2019 Jan van Katwijk, Lazy Chair Computing

SDRplay:

  • Copyright (C) SDRplay inc.

rtl-sdr:

rtl433.exe program:

  • Copyright Benjamin Larsson (merbanan on github)

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rtlsdr emulator: How to run rtlsdr software with an SDRplay device (renewed for windows)

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