How can I make a radio assistance call when there are no more resource crates in a location?

I can only access the 'Radio Assistance' menu when there are still resource crates in a location.

I'm playing the Steam Early Access version on the PC. The State of Decay wiki's "Radio" article states that (for the Xbox 360 version): "The active survivor can also call for field support through the radio. By pressing Down on the directional pad, the survivor can view the radio menu and choose an call to use."

However, I can't seem to find the equivalent key(s) on the PC, and can only access the Radio Assistance menu by selecting a resource crate and choosing to make a radio assistance call. So, another way of asking this question would be:
What is the equivalent key for the Xbox 360 version's D-pad down button (Radio Assistance) in the PC version?

The Radio Assistance menu can be used to build an outpost in the location one is making the call from. If a location where you can build an outpost doesn't have any resource crates anymore (either I already took it in my rucksack, or already taken by scavengers), can I still make a radio call and build an outpost there?

Another issue here is that the Radio Assistance menu is needed when you want to move to a new house / home site. How do I make a radio assistance call to move to a new house if there are no resource crates in that location?

As of the 2013-09-26 update, this bug has now been fixed. Related changelog:

fixed radio on left alt button

Pressing Left Alt should now make the radio assistance menu appear.

If you can't update or if the update does not work for you, try the fix detailed below:

The initial Steam Early Access version has no equivalent key for the Xbox 360 version's D-pad down button (Radio Assistance). However, there is a keybind fix:

Download the prototypeactionmap.xml file here and then go to the "State of Decay\Game" folder. Then, create a new folder inside it named "libs", and then open "libs" and then make a folder inside it named "config". Then, move prototypeactionmap.xml to the "config" folder you created.

The directory structure should look like this: State of Decay\Game\libs\config\prototypeactionmap.xml. You should now be able to make a radio assistance call even if there is no resource crate in a location.

The Radio Assistance key will be bound to Left ALT.

^{Keybind fix from: Undead Labs forums post by user, thexshadow}