Hi Tim,
I wasn't aware of that change myself, though I suspect it was made quite a while back.
The option to run individual PAW units as Base Stations was very useful in the early days when we needed 'actively transmitting' ground units to test airborne PAWs but that need has essentially been removed because of the ready availability of 'active' PAWs and of the custom designed ATOM Ground Station software. (but see below)
That, however, still leaves your question re 'testing your PAW without antennas' essentially unanswered.
The reason we shouldn't run transmitters without an effective antenna (or equivalent matched impedance 'dummy load') is to prevent damage to the output stage of the transmitter by the transmitted signal having nowhere to go and being reflected back into the transmitter. This is particularly important with high-power transmitters, though less so with PAW.
The significant change, however, is that PAW software has for some time now included an 'Aircraft Transmit Speed' feature (on the 'Configure Screen' just below 'Aircraft Type'). This was originally designed to prevent transmissions from essentially 'non-moving' aircraft on the ground - in order to reduce 'clutter' on displays and repeating audio alerts received by aircraft in close proximity (e.g. in the circuit). The 'Base Station' options were presumably removed at the same time, or shortly afterwards, though as I say I wasn't aware until now that this had been done.
The trigger threshold for Aircraft Transmit was originally set at a default of 10Kts* - which means that PAW wouldn't transmit when not moving, or when taxying extremely slowly, but I can't recall if this default is still current, so my advice would be to power up and go straight to the PAW/ Config Screen and check this setting. If it
isn't set at 10Kts (or higher) set it to this level and your unit won't transmit unless it is moving at this speed or above. Remember to review your setting if you decide you
do want your PAW to transmit when not moving (e.g. for testing) once you have connected the appropriate antenna, but please reset it to a sensible threshold before actual use.
*Remember that aircraft such as helicopters may need to set this threshold lower than 10Kts to keep PAW transmitting while in the hover.
I hope this helps clarify the situation.
Best Regards
Peter