You should able to use 802.11n, 802.11n with b/g compatibility, or 802.11b/g. The Radio Channel Selection which would normally be set on "Automatic". But there is another critical selection which is the radio "band" you are using. 802.11n operates on either a 5GHz band or the older more crowded 2.4GHz band while 802.11b/g protocols only operate on the 2.4GHz band. GIven your description, I suspect your MacBook is connecting on the 5GHz band using 802.11n. This is a faster connection generally with more range and subject to much less interference.

The original Time Capsule could operate on either the 2.4GHz band or the 5GHz band but those manufactured since March of 2009 can operate on both bands simultaneously. I have a late model Time Capsule setup for 802.11n with b/g compatibility. The Time Capsule creates two separate networks Bailey (5 GHz) and Bailey. My computers connect on the 5GHz band and my iPhone, iPad, and printers connect using 802.11g on the 2.4GHz band. Even better I can share data freely between the two networks.
  1. Determine what protocol and band your are connecting on by:
    1. Click on the Apple Menu > About this Mac
    2. Click on More Info to launch system profiler
    3. In the Contents column find Network and Select Airport
    4. under "Current Network Information" find PHY Mode and Channel and tell us what you find.
  2. Determine what your Time Capsule is capable of supporting:
    1. Open Airport Utility and select your Time Capsule.
    2. At the top of the window you should see something like
      Originally Posted By: Airport Utility
      Airport Utility found a Time Capsule (Simultaneous Dual-Band II)
      Let us know exactly what your find here


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