Coaxial connector for frequency generator input connection. This is NOT for the RG-213 cable, but the signal cable from the frequency generator. You need one.
Newark/Farnell part # 1169699 (link)
To connect the PA3 to the coax plug (frequency generator input) I used 10 cm of RG-58 cable. You may use RG-213, but it is overkill and the RG-213 is not easy to work with. The cheapest way to get some cable is probably to buy a standard RG-58 coax cable with plugs, and cut off the plugs.