Bon dia!
I will give my opinion without entering much in technical details, trying only to give some useful information at the level of game play. Take in to account that my direct experience about the matter is from 8 years ago...
About the walkie-talkies, you need to know that, in general terms, their range of available frequencies and their limited power output can provide a maximum distance of communication of about the range of sight in open terrain (between 4.5 and 5Km). This distance can be drastically shortened in an urban area and (in general terms) in any terrain with important obstacles cutting the line you can trace between the two communicators. Perhaps the effective range could be reduced to 1 to 2 Km. In that conditions, a good way to simplify the things would be: If there's an interrupted line of sight between us, we can communicate easily. If not, it's not an automatic task and you would need a roll to determine success.
I've got much more experience about backpack radios. I will suppose that you're talking about a VHF radios, the typical at platoon level. Their lower frequency and greater in power output usually makes them less vulnerable to the physical obstacles than the walkie-talkies. You could consider about 8 Km of effective range with the normal whip antenna and 4Km with the metallic-flexible antenna. Sorry, I do not know the correct English term for this type. Again, you can reduce the distance if there's a lot of obstacles, but, even in the worst conditions, you could consider that at 4km with the whip antenna and 2km with the flexible antenna, all communications attempts would be nearly an automatic success. Finally, this type of radio usually could be used with a 12m mast antenna (in a separate bag, of about 20Kg in weight) that can extend the maximum distance at about 30Km in optimum conditions. The task to deploy the mast usually implies two persons and can take about 5 to 10minutes depending of the training level of the operators. Again, a high position will help.
I hope it will be useful.
