RG-6 maybe?
might have been a RG-8 mini coax, most of these systems are 50 ohms for the RF network in these units, RG-58U, RG-8U, RG mini8, RG-213mil are all 50 ohm cables, there are many more 50 ohm cable also.
Where is a good spot to find connectors and crimping tools for this smaller cable? The picture is something like the connection on the existing cable.