Part 1 is a black, cubic, wall-wort type of thing.
It plugs into an ungrounded 120V outlet.
It’s only outlet is a coaxial, male, f-type screw threads.
On it is written:
Input 120VAC 60Hz
It was attached -via coax cable- to this thing that looks like a splitter. On the splitter, it says ARPI-2000 power inverter.
This splitter has 3x, differently labeled, male, f-type screw thread connections on it.
Is this a signal amplifier? Additionally, can I use it to amplify my (digital’) TV antenna’s signal?
It is probably a power supply for either an inline amplifier on a cable-TV or antenna mast mounted amp, or a power supply for an LNA (Low Noise Amplifier) for an older satellite system. Newer satellite receivers directly provide power to the LNA, so I’m going to stick with the first.