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