ADALM-PLUTO SDR Hack: Tune 70 MHz to 6 GHz and GQRX Install

Yesterday we posted an unboxing and a few tests with the PlutoSDR. On that post user rlwsdr commented and informed us that’s it’s actually possible to do a quick hack that changes the frequency range and bandwidth from 325 – 3800 MHz and 20 MHz up to 70 MHz to 6000 MHz and 56 MHz bandwidth. All that is needed to perform this hack is setting a device string on the PlutoSDR via a USB serial connection. This hack has been confirmed by Alex Csete and others on Twitter and ourselves. It works for both RX and TX.

Alexander Csete (programmer of GQRX) also posted instructions in a comment on our last post that explained how to get GQRX running with the PlutoSDR. 

Also in the last post we mentioned that all distributors were out of stock, but a few hours after that post went out Digikey restocked and they now have (at the time of this post) 184 units left at the $99 USD price.

Frequency and Bandwidth Hack

Thanks to ‘rlwsdr’ and Alexandru Csete for bringing attention to this hack.

It seems that the current shipping version of the PlutoSDR uses the AD9363 chip which is restricted to a frequency range of 325 – 3800 MHz and bandwidth of 20 MHz. However, the higher end AD9364 chip which can support 70 MHz to 6000 MHz and 56 MHz of bandwidth is supposedly nearly identical to the AD9363 chip. The PlutoSDR can be tricked into seeing a AD9364 chip simply by changing a device string on the unit, but it’s not guaranteed to give the full tuning range and bandwidth for every single unit. It’s possible that the AD9363 chips are actually AD9364 chips that failed performance QC checks and have just been rebranded as a lower end model, or that a cheaper silicon process is used with the lower end chip.

The instructions for performing this hack are actually detailed by the official Analog.com PlutoSDR wiki on the customization page. Just search for the heading “Updating to the AD9364”. The instructions state that this is only for older PlutoSDR units which actually came with the AD9364 chip, but it seems to work with the newer PlutoSDR units that have the AD9363 chips as well.

Simply plug the PlutoSDR in, and connect to it via a serial connection. On Windows you can use a program like PuTTY for this purpose. First search in device manager for the COM port assigned to your PlutoSDR, and then input this into PuTTY leaving the speed at 9600. You can then log in and set the environment variables using the lines provided in the wiki. Now in GNU Radio, GQRX etc you should be able to tune down to 70 MHz and up to 6 GHz and set the bandwidth to 56 MHz.

The images below show the PlutoSDR serial connection screen and the commands you need to type, the PlutoSDR tuning down to broadcast FM frequencies at 100 MHz, and a TX test at 70.1 MHz. It was found that the strength of the TX is a bit lower outside the official range, but can be increased by turning off the attenuation setting.

Setting up the GQRX Experimental Branch for the PlutoSDR

First set up GNU Radio and gr-iio using the instructions from this Reddit thread.

Now install gr-osmosdr-gqrx with the iiodev branch.

git clone https://github.com/csete/gr-osmosdr-gqrx
cd gr-osmosdr-gqrx/
git checkout plutosdr
mkdir build
cd build/
cmake ../
make
sudo make install
sudo ldconfig

Install the GQRX prerequisites

sudo apt-get install git build-essential cmake qtbase5-dev qt5-default qtscript5-dev libssl-dev qttools5-dev qttools5-dev-tools qtmultimedia5-dev libqt5svg5-dev libqt5webkit5-dev libsdl2-dev libasound2 libxmu-dev libxi-dev freeglut3-dev libasound2-dev libjack-jackd2-dev libxrandr-dev libqt5xmlpatterns5-dev libqt5xmlpatterns5 libqt5xmlpatterns5-private-dev pulseaudio

Install GQRX

git clone https://github.com/csete/gqrx.git gqrx.git
cd gqrx.git
mkdir build
cd build
cmake ..
make
sudo make install

Now GQRX should be ready to use the PlutoSDR. In the GQRX confiuguration screen select the device as Other or PlutoSDR and set the device string as “plutosdr=0”. Then you can set your sample rate and RF bandwidth, decimation etc. If you’ve done the frequency range hack then remember to select “No limits” in GQRX so that you can actually tune down further.

Note that in VMWare Lubuntu we were only able to get stable audio from the PlutoSDR and GQRX at a maximum of 3 MHz. Anywhere between 3 – 60 MHz bandwidth the PlutoSDR and GQRX spectrum and waterfall runs smoothly, but the audio is crackly. Might be a VMWare problem, or maybe something that can be fixed in later GQRX releases.

We also tested the PlutoSDR together with the SpyVerter upconverter for HF reception. It seemed to work well.

The images below show the PlutoSDR working in GQRX. The images of the 2.4 GHz and 1.8 GHz bands show that there is little to no attenuation at the edges of the 60 MHz bandwidth, so the upgrade from 20 MHz to 60 MHz is working well.

Conclusion

So with this hack the PlutoSDR is a much nicer unit that really makes an interesting and affordable choice for those wanting to upgrade from the RTL-SDR. Combined with a SpyVerter upconverter the unit should also be able to receive HF signals quite easily, so this gives a total cost of $148 for a DC to 6 GHz receiving system with TX capability, 12-bit ADC resolution and up to 56 MHz of bandwidth.

Of course we still need to confirm what the performance of the unit is like, especially in the frequency ranges opened up by the hacks and in regards to strong signal handling. We will test those in the coming weeks. If it handles those well and other software developers support it in their software then despite the unit being advertised as a learning module for students, it might become one of the best and most affordable general purpose SDRs available.