It's a program called RTL SDR. It uses a dongle, which I ordered from China for something like $7.00. You can buy an an SDR RTL dongle now. Search Amazon and E-bay.I was even able to get an antenna that most places don't carry, a Long Range Mixed with low VHF added in addition to the usual high vhf and uhf Part Number 148281. With the Avant X I could have just as easily gone with the 148280 which comes with no power supply as the Avant X will power the preamp so you don't need the power injector. As a point of reference to decipher the info given at Televes, Low VHF is referred to as Band I, High VHF is Band III. Band II is FM Radio.
What did you use to get the neat graphs you show here? I will be using a borrowed Televes meter. I'm thinking of buying the one that supports ATSC 3.0 and HVEC so one can actually view ATSC 3.0 content to verify. The meter I borrowed has an ethernet port so it is easy to use a web browser as well and there is a phone app one can download.
There was a comprehensive thread on it on the now defunct Hi-def forum out of Canada.
Rabbit 73 here, has helped me with it but the idea was originally introduced by Pete Higgins who showed me the way originally. .
Low cost Spectrum Analyzer Digital TV and Mobile DTV
Good luck !