Either plant the cogwave jammer on the Wonder Wheel or dispose of it in the nearby trash compactor.
Return to Calvert Mansion.
Desmond reveals the brain to be Professor Calvert, a brilliant pre-War scientist and the last remaining member of the Calvert family. Desmond has a long history of tampering with the Calvert family, going as far as staging a scandal between a Presidential nominee and a dog. He then tells you to plant a cogwave jammer on the Wonder Wheel that will disrupt the messages that Calvert has been trying to send throughout the Point Lookout area. Once you near the Wonder Wheel, you can hear Calvert's voice trying to persuade you to destroy the device that Desmond gave you.
Once you reach the Wonder Wheel, you have two options, but don't worry too much about them, they have no effect on karma or main storyline. Desmond, however, will react differently depending on your choice.
Side with Desmond
Plant the jammer and activate the Wonder Wheel. After this is done, Calvert's voice breaks up as the jammer does its job, then a group of tribals will attack you, and all unnamed tribals remaining at the Cathedral will become hostile (the named tribals will likely join them if a fight breaks out unless the unnamed tribe members are killed unobserved).
Return to Desmond. When you approach the Calvert Mansion, it immediately explodes. As a result of the explosion, you are knocked to the ground. Once you stand back up, walk to the middle of the house and find Desmond in his Panic Room. He begins to tell you how angry he is that his "pups" (Freki and Geri) were killed and that Calvert was so close to the mansion. He then states that the 200 year long feud between him and Calvert is going to end right now.
Side with Calvert
Destroy the jammer. Follow Calvert's instruction to place it in a nearby trash compactor. Calvert will tell you to return to the mansion, which is then destroyed in a huge explosion. There is minor loot in the Panic Room (including ammunition, food, a Nuka-Cola Quantum and two very rare gum drops), reached through a hatch in the center of the ruins.
You'll then advance to the same place as the second decision, the lighthouse, and the actual decision of who to kill is basically delayed via dialog until the very end. Also, you'll find Desmond isn't dead, but following Calvert in the lighthouse to kill him.
In the next stage of the quest, Desmond will be hostile. If you kill him and go alone through the lighthouse, there is significantly more ammunition and loot to be found.
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PCPlayStation 3Xbox 360 Even after destroying the Cogwave Jammer in the trash compactor, you can still walk up to the Ferris wheel and it has the "Activate Ferris Wheel" option, which if you click it, it says "The Cogwave Jammer has been installed.", when it really hasn't been. (All Versions) Doing so may leave you unable to complete the quest with the "Return to Mansion" objective never being able to be satisfied.
PC If you fast travel to a different area while Professor Calvert is telling you to destroy the Cogwave Jammer you may not be able to finish the quest. You can't plant it or destroy it until the power turns on, which is after Professor Calvert is done talking. When you come back to the Ferris wheel or trash compactor later it will tell you that the power needs to be turned on, and there is no way to do it.
PlayStation 3 When approaching the Ferris wheel, the game may crash/freeze requiring a manual restart. This can make the quest nearly impossible to complete.