Normally after we see a challenge utilizing a software-defined radio (SDR), the SDR’s inputs and outputs are related to antennae, however [FromConceptToCircuit]’s challenge related an ADALM-Pluto SDR to an RF bridge and some passive elements to make a surprisingly efficient community analyzer (half two of the video).
The community analyzer measures two properties of the circuit to which it’s related: return loss (S11) and insertion acquire or loss (S21). To measure S21, the SDR feeds a collection of tones to the machine below check, and reads the machine’s output from one of many SDR’s inputs. By evaluating the amplitude of the enter to the machine’s output, a Python program can calculate S21 over the vary of examined frequencies. To seek out S11, [FromConceptToCircuit] put an RF bridge according to the machine being examined and related the bridge’s output to the SDR’s second enter. This allowed this system to calculate the machine’s impedance, and from that S11.
The RF bridge and different elements introduce some inaccuracies to the measurements, so earlier than making some other measurements, the system is calibrated with each a via connection and an open circuit instead of the examined machine. The RF bridge’s directivity was the largest limiting issue; switch again from the bridge’s output line induced the reflection below load to exceed the reflection of an open circuit in some frequency ranges, at which level the analyzer couldn’t precisely function.
[FromConceptToCircuit] was finally capable of make measurements all through a lot of the 0.1-3 GHz vary with a dynamic vary of at the very least 10 dB, and expects a extra directive RF bridge to present even higher outcomes. If you happen to’d wish to repeat the experiment, he’s made his Python program obtainable on GitHub.
We’ve beforehand seen [FromConceptToCircuit] use the Pluto SDR to make a spectrum analyzer. We’ve additionally featured a information to the Pluto, lined a challenge that improved its frequency stability, and seen it used to transmit video.
