Chapter 7: OOC
I was running around all weekend, hence my lack of response, but I think it shouldn't be too difficult for Yuu to create some radios for temporary use. You could also go an buy some sort of radios, though that would increase the risk of some party being able to eavesdrop on them versus the custom-built ones.
If he's designing a purely technology based device he'll need to use Know: Tech skill for design, and if it's a Nether device he'll use Know: Nether. If the later he'll also need to find some nether batteries to change the devices. For actually constructing the devices he'll need to make a Craft: Electronics check.
Here's the basic options you're looking at:
Nether Comms Devices: Communication Power w/Area Extra (omnidirectional)
1) Level 2 (100' range): Design check: TV 19 (2hrs), Craft: TV 14, 16 hrs
2) Level 3 (1000' range): Design check: TV 21 (3hrs), Craft: TV 16, 24 hrs
3) Level 2 (100' range) + encrypted: Design check: TV 20 (2.5hrs), Craft: TV 15, 20hrs
4) Level 3 (1000' range) + encrypted: Design check: TV 22 (3.5hrs), Craft: TV 17, 28hrs
You can reduce the crafting time by half by increasing the TV by 5, making it quite difficult. You cannot take 20 on the crafting check, but you can take 10.
We can assume you essentially had most of a full day of Kahl'yun day, probably about 30 hours of functional time, before the actual meeting.