The BNC cable is used to sync the 2 units together for scalar mode. The TG will function without necessarily being tethered to the SA. In CW (non sweep) mode the TG will produce an RF signal on whatever frequency you tell it to go to.
Simple experiment: Why don’t you try it.
Also note that the TG44 is much happier loading into a 50 ohm load so the admonition of using a 20 db attenuator in series with an unknown load will help flatten out the power level while adjusting the antenna.
