I have a McIntosh MI 3 that was made in the early 1960s. It is called a Maximum Performance Indicator. It has a small oscilloscope built into the front panel. You would connect this unit to a MacIntosh tuner (although I believe that you could use it with other tuners as well). The oscilloscope would show the amount of multipath present in the signal so you could rotate your antenna (many people who owned this unit had a motorized antenna that could go up and down and around) and optimize the antenna's position for minimum multipath distortion. It's pretty cool to see the 'scope present the signal.
Barry Kohan
Barry Kohan