Hi Webster,
The 1242 AP will require at least 2 External Antennas. Have a look (there are Dual RP-TNC connectors for 2.4GHz b/g radio and 5 GHz a radio);
Antenna Connectors - AP 1242
2.4 GHz
Dual RP-TNC connectors
5 GHz
Dual RP-TNC connectors
Cisco Aironet 2.4 GHz and 5 GHz Antennas and Accessories
The choice you make will depend on the Coverage pattern you desire. There are a number of Models for the 1242 listed here;
http://www.cisco.com/en/US/products/ps6521/products_data_sheet09186a008022b11b.html
Hope this helps!
Rob
