People often do not realize that ATSC tuners are a fairly recent thing, only being mandated for all TVs built after March 1, 2007 for the big DTV transition that occurred June 12, 2009 for all the big network stations.
Larry Weber's prototype 60" color plasma TV of 1994 used a Panasonic panel, and Panasonic plasma TVs dropped to prices the middle class could afford around 2001. Needless to say, any tuner in such an old TV would be NTSC, and the last low-powered NTSC stations in the United States ceased transmitting on September 1, 2015.
So if it really is such an older Panasonic plasma, it would need an external tuner "converter box" to receive any over-the-air stations.
Hold on to your hat--on November 17, 2017, the FCC voted to authorize voluntary deployment of ATSC 3.0 which isn't backwards compatible with any current TVs using ATSC 1.0 tuners. Broadcasters prefer the new standard as they can squeeze more channels into less bandwidth, so this means starting in 5 years or so there will be fewer and fewer channels for your current TV unless you want to attach a external tuner box to that as well.