go to goldenrod city and go to the radio station talk to all of the women behing the counter and one of them will ask you to complete a number of questions, once you have answerd them you will have the radio card and the gym leader whitney will go back to her gym so you can battle her.
hope this helped :).
Chat with our AI personalities
After you fix the power plant go back to the kanto radio station and the owner will give you the card.
Whitney is in the radio tower. She is trying to get the radio card. You have to beat the quiz and she will return to her gym
you put the blinking dot on your radio to the center on the top and then press a on snorlax
In order to get the Card Key in "Pokémon HeartGold," you need to get to the Director who will be in the Underground Tunnel in Goldenrod City after Team Rocket has taken over the Goldenrod Radio Tower. The Director will give you the Card Key which will open up a Card Key door in the Radio Tower which will assist you in defeating Team Rocket.
You can get to the radio tower in HeartGold by going to Goldenrod City and if you go there there is a daily drawing corner and a quiz to get the radio card. If there is someine blocking you, then go to the underground shop, get the Team Rocket uniform, and they shall let you in.