From Bulbapedia, the community-driven Pokémon encyclopedia.
Pokédex Show (Japanese: よくわかる ポケモンずかん Understanding the Pokémon Gallery) is a radio show available only in Johto in Generation II. It operates on the radio frequency 4.5 from 4 AM to 10 AM each day. All the other times, Professor Oak's Pokémon Talk is broadcasted on that frequency. This show is not hosted by any known DJ.
The Pokédex Show randomly generates Pokédex descriptions out of the Pokémon that the player has caught and stored in the Pokédex.
The show is completely gone in Generation IV (along with Lucky Channel and all of Kanto's shows). Instead, Professor Oak's Pokémon Talk now airs all the day.