I believe what you're describing is a standard coaxial ("coax") cable. From the outside in, you will find a layer of insulation, a braided wire "shield", an insulator, and an inner core conductor. The inner conductor (often solid, but sometimes stranded) is what carries the actual signal. The shield is connected to ground (probably inside the radio) to prevent interference.
How is your wire broken? If it has been cut clean through, you can probably crimp the inner core together, wrap some electrical tape around it, connect the shield across the gap, and wrap some more tape and it will work. Your signal quality will be degraded because the shield isn't continuous anymore, and the crimp may also cause a small loss of signal. To get better performance, you can try to find some coax connectors for your size cable (maybe something like a BNC connector) and use them to connect the two halves with less signal loss. If you want it to be like-new, you need to replace the entire length of cable.
1979 Gulfstar 37 Laissez Faire