Coaxial is a rg59
From the manual:
Detection Loop
Track width : max. 10 m / 33 ft
Coax to decoder : 75 Ohms, double shield, max.length 200 m / 660 ft
To check the coax cable: use Ohmmeter to measure Ohms
between center pin and outer metal the of BNC connector. It
should read 95 to 105 kOhm.
Also the yellow wires into the connection box can be measured: it
should read 95 to 105 kOhm (470 Ohm resistor disconnected).