Found these installed in an old building, and they were apparently working with an antenna in the recent past. Has anyone ever used such a thing, and would they be useful in a modern setup?
They can be useful if they are still working. They are designed to put out a strong signal for large distribution systems. The tilt controls allow you to make the high and low channels about the same strength, because the high channels get weaker faster on long coax runs.
The -30 and -20 dB markings are not the amp gain. They tell you how much weaker the sample port is than the main output port. This allows you to adjust the gain of the amp without disturbing the main output when the amp is in use.
The technician would connect his signal level meter (which reads in dBmV) to the sample port for a reading, and add 20 or 30 dB to the reading on his meter to know what the output signal was.
