Before you do too much you need to check the receiver settings. Menu>Settings>Satelllite>Repeat Satellite Setup. It's quite possible that your home setup is SWM and your portable antenna is not. If you get in there and see the switch type set to SWM you have your problem identified. Now, just figure out which LNB you are using and set that be sure to set the switch to Multiswitch and go to the signal meter and point the antenna.
If you recall, does your HR24 in the living room have only 1 coax cable running into it? If so, you whole house is setup for SWM.