Still in the Dark: Started by speaking to Dobson. Dobson can be killed or tricked into leaving (requires Speech 50) during the quest. However, you cannot talk to him if your reputation with the NCR is bad. Alternatively, he can be warned about the Brotherhood of Steel; however, this will cause the Courier to fail the quest. Dobson will remove the collar from the Courier's neck and the Brotherhood of Steel will attack. If he survives, he returns to the base and the Courier will gain fame with the NCR.
If you choose to smash the broken Ham radio while Dobson is looking, he will become hostile and attack you. However, if you can make him leave the bunker after stealing the supplies and then smash the radio, the quest should complete and Dobson will not attack you.
If you choose the speech check to complete the objectives. The next time you return to the bunker you can still find him there about to depart. Beware of a great amount of grenade bouquets which are enough to fill the whole place with explosions; it seems Dobson prepared them for the powder gangers.
ps3 Dobson may appear in the Southern Hidden Valley Bunker, although he will be invisible. The "talk" button will still appear but it will do nothing. Shooting near him in this state will make him say things like, "Watch where you're shooting". [verified]
xbox360 Sometimes, if Dobson survives the encounter with the Brotherhood, the player may still not gain any reputation from the NCR. [verified]
pcxbox360 He sometimes may be found just outside of Hidden Valley, although everything else is the same except his position. You can still talk to him about leaving the bunker. [verified]