Software Defined Radio
- 1 Introduction
- 2 Supported Devices
- 3 Supported Devices with closed-source drivers
- 4 Unsupported Devices
- 5 RTL-SDR Support
- 6 Airspy support
- 7 SDRPlay support
- 8 USRP support
- 9 LimeSDR support
- 10 PlutoSDR support
- 11 References
Built upon GNU Radio and SoapySDR by using the gr-soapy module SatNOGS supports a large variety of Software-Defined Radios (SDRs). The gr-soapy module was developed in the SDR Makerspace and is maintained by Libre Space Foundation to bring the vendor-neutral SDR support by SoapySDR to the flexible gnuradio ecosystem.
The most cost-effective solution is to use an RTL-SDR with a Raspberry Pi. More advanced SDRs are also used, but they require more processing power and thus might require a more powerful computing platform than the Raspberry Pi.
SoapySDR supports SDR devices through runtime-loadable modules . You can find all available modules in the SoapySDR wiki (see right column). Most SDR modules are installed by default when setting up a SatNOGS station.
The following SDRs are supported by SatNOGS. SatNOGS uses the RTL-SDR as the recommended beginner signal receiver and tuner. The more advanced SDRs may require more processing power than a Raspberry Pi 3b or 4 can offer.
Supported Devices with closed-source drivers
Unfortunately some vendors require closed-source drivers in their SoapySDR modules and thus those modules or dependencies can't be redistributed by others. Thus they must be manually installed by the user. The following devices require closed-source drivers:
- HackRF One (not compatible with the SatNOGS client on Raspberry Pi)
- USRP2 (not compatible with the SatNOGS client on Raspberry Pi)
The RTL-SDR is based on two chips -- the versatile RTL2832U chip and the R820T tuner. The RTL-SDR is currently the cheapest, most common, and most performing solution available in terms of general sensitivity having a frequency range of 24 – 1766 MHz. A metal enclosure with SMA connector is preferred, along with a stable TCXO (low ppm). HF coverage is optional.
Using RTL-SDR.com V3 Dongle's Bias-T Power Supply
The RTL-SDR.com V3 dongle has a built in software activated Bias-T voltage supply intended to be used for applications such as powering inline LNAs (Low Noise Amplifiers). There are several ways to turn on the voltage, but through initial testing (as of this writing, 17 Aug 2019) it seems that the following procedure works best.
The below relates to Raspberry Pi installs only. No testing has been performed on other systems as of yet.
- Raspberry Pi running Raspbian Buster or newer (latest release of SatNogs image, 2019091100, is demonstrated to work)
- RTL-SDR.com V3 SDR dongle
- RTL-SDR.com Bias-T Software Switch for linux systems
- LNA capable of being powered via feedline coax (note that some LNAs need modifications to be powered by the coax, and some cannot be powered by the coax at all. Check the specifications for your LNA prior to attempting to turn on the Bias-T power supply)
Instructions for installing RTL-SDR.com Bias-T Software Switch
- Log into your SatNogs station either directly or via SSH
- If your station does not have cmake installed (SatNogs Image 2019091100 does not), install cmake with
sudo apt install cmake
- Clone the source for the Bias-T software switch with
git clone https://github.com/rtlsdrblog/rtl_biast
cmake ..(if you get a
LibUSB 1.0 required to compile rtl-sdrerror here, then do
sudo apt install libusb-1.0-0-devprior to attempting
The software switch should now be installed in the "src" directory. If you
cd src, you can turn on the bias-t with the command
./rtl_biast -b 1 and turn it off with
./rtl_biast -b 0. Note that the developers of this switch have warned against attempting to
sudo make install so that this command can be executed from ouside the src directory. Testing has shown this warning to be accurate, so don't plan on running these commands from anywhere but the src directory, or else be sure to use the full path.
Switching the Bias-T on should yield between 4.5V and 5.0V across the center conductor and shield of the coax. The voltage should rise almost instantly. When switched off, the voltage seems to decrease gradually, over 5 to 10 seconds.
Instructions to activate the bias-t for SatNogs Observations automatically:
- Log into your SatNogs station either directly or via SSH
SATNOGS_RF_GAIN, enter a low gain value supported by your RTL-SDR.com V3 dongle (entering
rtl_testat the command line prior to starting
satnogs-setupwill give you all allowable values of RF gain) and select
/home/pi/rtl_biast/build/src/rtl_biast -b 1and select
/home/pi/rtl_biast/build/src/rtl_biast -b 0and select
Apply(allow system to update and hit enter when prompted)
Your station is now set up to turn the Bias-T on for each scheduled observation (using the
SATNOGS_PRE_OBSERVATION_SCRIPT string) and then turn it off at the conclusion of each observation (using the
You should now schedule several observations to fine tune the
SATNOGS_RF_GAIN value to get the best S/N performance for your station. Some have reported needing zero RF gain, others have reported low RF gain required (between 5 and 10 db), and others have said they see little benefit even with very high gain. Each station will be different.
E4000 Tuner Gain Settings
The RTLSDR Driver exposes six (!) IF gain settings (IF1 through IF6) for the E4000 tuner, along with a TUNER gain setting, which is actually a combined LNA and Mixer gain control. Details on the gain stages are available in page 28 of the E4000 data-sheet here: https://www.nooelec.com/files/e4000datasheet.pdf
When you follow the 'Setting the Gain' guide, all gain sliders (IF1 through IF6, and TUNER) should be presented in SoapySDR, allowing the user to adjust them to optimise for best performance. Once the correct values have been determined, you will need to define these specifically in satnogs-setup as follows:
(Replacing the values in the line above with the ones you determined)
R820T Gain Settings
Unfortunately librtlsdr only exposes a single gain control for the R820T/T2 tuners, even though multiple gain adjustments are available. Use the standard SATNOGS_RF_GAIN option, with a gain between 0 and 42 (dB), as optimised for your station via the 'Setting the Gain' guide.
required SoapySDR module: SoapyAirspy
Note than none of the settings below should be entered with the " " around the value. This is only for better readability in the Wiki !
There are two possible gain modes:
"Overall": (default) Use a single gain value. Set the overall gain with
"Settings Field": Use granular gain values. Set the different gain stages separately:
- without pre-amp:
- with pre-amp:
"LNA=9,MIX=6,VGA=11"(used in 49 - OZ7SAT)
- without pre-amp:
For reference see also the Airspy driver library linearity gain settings in libairspy/src/airspy.c#L117-L122.
- Airspy R2:
2.5e6 or 10e6
- Airspy Mini:
3e6 or 6e6
- Airspy HF+:
If you want to activate the integrated bias tee, set
Bit packing ("Enable packing 4 12-bit samples into 3 16-bit words for 25% less USB trafic.") could be enabled with
"bitpacking=true" (untested). Device arguments can be concatenated with comma as delimiter.
required SoapySDR module: SoapySDRPlay
SATNOGS_ANTENNA="Tuner 1 50 ohm"
Note that 14-bits ADC resolution is only available when using sample rates below 6.048 MSPS, above which the resolution is reduced gradually to 12, 10, and 8 bits.
Vendor: Ettus Research
required SoapySDR module: SoapyUHD
Recent USRPs that use the Analog Devices AD9361 RFIC can use almost arbitrary sample rates and analog bandwidth settings. It can be an advantage to set the sample rate as high as the host computer can handle and the analog bandwidth to as narrow as meaningful. The following settings worked well for a USRP B210 when using cross-yagis and good SSB low-noise amplifiers:
- on the B200 your Antenna options are TX/RX and RX2, be sure you select the right option for your configuration!
Vendor: Lime microsystems
required SoapySDR module: SoapyLMS7 wrapper
(untested, copied from station 1378)
Vendor: Analog Devices
required SoapySDR module: SoapyPlutoSDR