I started to go ahead and pop in the new RSC cards to play around with and I started thinking. Is it bad for the radios to run without antennas.???
there is nothing wrong with not having an antenna
Except that much of your power gets reflected back into the PA (i.e. very high SWR), which is not healthy for it. Most systems will try to shunt that power to ground (and/or cut the output power, and/or dump it into a resistor), but a portion will still come back on the transmitter.
Over time, it can damage the PA and other components; distorting the output signal. reducing the reciever’s sensitivity, and reducing the radio’s lifespan.
Some radios, like big FM transmitters, satelite uplinks, and other powerfull and/or expensive radios, will stand a very good chance of blowing if you don’t connect an antenna. One of the places we colo in has a dead $25000 65KW tetrode sitting on the shelf, there as a reminder to double check everything. It melted it’s control grid after running just 20 minutes, due to the reflections created by a dented coax line (and an already broken monitor circuit, which should have prevented the thing from powering up like that in the first place).
For the most part, the sort of radios used in our line of work are very low power, are not exactly precision instruments, and are very inexpensive. So, the risk is low, both in terms of the likelyhood of damage, and in terms of loss if it does die.
Still, on principle, I would always attach an antenna, it’s a good habit.