I was trying to connect my new Airport Express (2gen, MC414RS/A, Country:Ukraine) to Airport Extreme (5gen, Norwegian, Country:Norway) using 5GHz (Auto: Channel 100). I believe both countries allow channel 100 in Auto mode. The result is Express cannot connect on channel 100 (no 5GHz network is found). Workaround is to fix 5GHz channel to lower one (36,40,44,48). But those fixed channels gives significant speed degradation if compared to higher channels.
The problem I believe in wrong list of supported 5GHz channel in Ukraine. List is outdated. Frequency plan was updated at September, 2012. Since than next channels are allowed:
802.11 b/g/n 2.4 GHz:
2400-2483,5 MHz – Wi-Fi channels 1-13
802.11 a/n 5 GHz:
5150-5250 MHz – Wi-Fi channels 34 – 48
5250-5300 MHz – Wi-Fi channels 52 – 56
5300-5350 MHz – Wi-Fi channels 60 – 64
5470-5670 MHz – Wi-Fi channels 100 – 132
5725-5850 MHz – Wi-Fi channels 149 – 165
But instead of that we have something similar to Russia (I am also not sure that all Russian channels are properly listed.
Must be something like
5150-5350 MHz - Wi-Fi channels 34 – 64
5650-6425 MHz - Wi-Fi channels 132 – 165
Official documents for Ukraine (it is in Ukrainian, but search for 802.11 can give the overview):
Official documents for Russia:
http://minsvyaz.ru/ru/doc/index.php?id_4=701 (p256, p264)
Would be nice if Apple could investigate the issue and update Airports firmware to allow more channels for Ukraine (and Russia maybe).