The detection loop is what detects the transponders going over it. It is typically buried beneath the track surface or suspended above it. The ends of the loop connect to the coax (connection box).
The connection box (coax cable) is what connects the detection loop to the decoder box. It contains special circuitry to reduce noise and missed transponder crossings. The end of the coax has 2 leads which connect to the detection loop
NOTE: Bury the loop in a rectangle fashion, approximate 12 inches apart. Trim excess wire evenly on both sides.