Not a bad idea but a few things to keep in mind.
- The sample rate on an Arduino is pretty low, depending on which model you have it may only be a few MHz and the absolute best you can theoretically possibly achieve with your home o-scope bandwidth is half the Arduino clock frequency. You'll also have to cast off the Arduino language and start moving to C/assembly to get the full performance out of it.
-The dynamic range on the Arduino ADCs is pretty low. It's going to be limited by the number of bits in the Arduino ADC.
-The input on an Arduino ADC is going to be either very low or very high impedance. This is also common on lower frequency scopes (low frequency in the case being 1GHz or less bandwidth) but if you try driving your input directly the impedance mismatch from the RF is going to cause poor signal and lots of noise on your measurement.
I don't know what SDR you have but it might be suitable for the signal capture and you can probably gin up some filters in post processing to approximate a Spectrum analyzer. If you have a source and 2 directional bridge couplers you could use it to make a poor mans Scalar Network Analyzer. A noise generator or a swept tone (Chirp) can be used in both these cases. The article you linked basically did a 1-port Network analyzer using the bridge coupler and used to to measure VSWR.
A lot of modern oscilloscopes, even hobby ones, now include the ability to capture scope traces to a PC and an FFT math function. You're going to be limited in frequency without a downconverter but it's a good way to go on a budget when working on a bench. The Rigol's are a lot better than they were when they first came out and make a good hobby scope for a reasonable price. If you can be spendy, the Keysight hobby level scopes are a joy to use. Best bet on a budget is to troll the internet for an old Tektronix, Lecroy, or HP/Agilent/Keysight but you'll probably not get something with fast trace capture or a built in FFT.
All of that said, making test equipment out of your Arduino is a great hobby project that will teach you tons of useful engineering. I highly recommend it!
I don't know what SDR you have but it might be suitable for the signal capture and you can probably gin up some filters in post processing to approximate a Spectrum analyzer. If you have a source and 2 directional bridge couplers you could use it to make a poor mans Scalar Network Analyzer. A noise generator or a swept tone (Chirp) can be used in both these cases. The article you linked basically did a 1-port Network analyzer using the bridge coupler and used to to measure VSWR.
A lot of modern oscilloscopes, even hobby ones, now include the ability to capture scope traces to a PC and an FFT math function. You're going to be limited in frequency without a downconverter but it's a good way to go on a budget when working on a bench. The Rigol's are a lot better than they were when they first came out and make a good hobby scope for a reasonable price. If you can be spendy, the Keysight hobby level scopes are a joy to use. Best bet on a budget is to troll the internet for an old Tektronix, Lecroy, or HP/Agilent/Keysight but you'll probably not get something with fast trace capture or a built in FFT.
All of that said, making test equipment out of your Arduino is a great hobby project that will teach you tons of useful engineering. I highly recommend it!