As jpeg1 says go into settings and in smart wifi disable "channel optimisation" and then rename the ssid's of the 2 networks (call them xxx2 & xxx5 - use same password) save/apply changes and both networks will now be separate and identifiable by your devices and you can connect each to the one ypu choose
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John
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My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.