| 455 / | HD | TELECOMMUNICATIONS | 
| 39 | DF | TRANSMITTER AND RECEIVER AT SEPARATE STATIONS {14} | 
| 500 | DF | .~ Plural transmitters or receivers (i.e., more than two stations) {4} | 
| 501 | DF | .~.~ Noise, distortion, or singing reduction {2} | 
| 502 | DF | .~.~.~ Synchronized stations {1} | 
| 503 |  | .~.~.~.~ Simulcast system |