What is the national calling frequency for FM simplex operations in the 2-meter band?
Why By long-standing US band plan convention, 146.520 MHz is the national FM simplex calling frequency on 2 meters. Simplex means transmitting and receiving on the same frequency with no repeater, so hams monitor 146.52 to make contact and then typically move to another simplex frequency for the actual conversation. It is a voluntary band plan, not an FCC rule, but it is universally followed, and many mobile rigs have a one-button 'call' key preset to it.
Watch out 446.000 MHz is the national FM simplex calling frequency, but for the 70 cm band, not 2 meters; 432.100 MHz is the 70 cm weak-signal SSB/CW calling frequency.
"Fifty-two for two meters": 146.52 FM simplex. Its 70 cm cousin is 446.00.