are there any diagnostics to establish which is the best wireless channel, without using trial and error?
If you're on a Mac (10.8.4 or later) they've built in a Wireless Diagnostic Utility
From Apple: About Wireless Diagnostics
From MacWorld: Troubleshoot your wireless network with Wi-Fi Diagnostics | Macworld
The inSSIDer application may help you with this
There have been a couple suggestions here, hopefully one of these works for you. If you are experiencing wireless connectivity challenges and are using a Shaw wireless modem, just let me know. I'd be happy to assist further.
Retrieving data ...