I notice a sidebar listing different kinds of support ranges depending on how far away from each other we are. What is the difference? Can we be in squad mode if we're in the long range vox communication one?

Orixes said:

The sidebar lists how far away you can be from another space marine and still be in support range. The range of a Vox isn't what matters, only the range listed on that sidebar.

Yeah, the range of your vox doesn't matter - that's just how the squad are co-ordinating their movements for squad mode. Those movements would be pointless beyond those ranges, both for general tactical concerns and how experienced the squad is with working together.

Rookie Deathwatch members (Ranks 1-3) can only really work together with visual contact and only within 30 metres of each other. As they get more experienced, they learn to co-ordinate with different levels of contact and over longer distances. And if you need to co-ordinate with someone more than 120 metres away (which is support range for Ranks 7 and up), then you're not really working at squad-level co-operative tactics anymore.