A while ago I wrote about how to use the HackRF One as a spectrum analyzer, and mentioned that apart from using its sweep functionality, it could also be used as a real-time 20 MHz spectrum analyzer using any SDR software. I now had to learn about its limitations and possible pitfalls when using it this way.
I wanted to look at the spectrum put out by an RF transmitter when transmitting a simple sine wave, i.e., an unmodulated carrier. In particular, I wanted to know about any nearby spurs, so looking at it with a high-bandwidth SDR seemed to be a good idea. So I connected the transmitter to the HackRF One, using appropriate attenuation. Looking at the spectrum put out by the transmitter gave me a bit of a shock:
I recently got my hands on a USB microphone, namely the Samson Meteor Mic, a large diaphragm electret condenser microphone that not only looks cute but also has overall good reviews online. However, when testing the microphone I was rather disappointed by the annoying background noise that is clearly audible when turning up the volume of the microphone. Have a listen:
We hear two things here: One is relatively normal microphone hiss. The other is a high-pitched noise which you really do not want to have in your recordings. Let’s have a look at the spectrum of the recorded noise, using Audacity and its spectrum analysis (i.e., an FFT):
The HackRF One is a popular software defined radio (SDR) device, supporting not only reception but also the transmission of radio signals in the range between 1 MHz and 6 GHz. A new feature in the HackRF firmware now allows using it as a spectrum analyzer over the full 6 GHz range.