Antenna Cable Length
This is the length of the connecting cable between the antenna and the receiver as determined by the manufacturer. Cutting this cable shorter or splicing it longer spoils the length and impedance match; the result is a loss in signal level and a noticeable drop in range in the field. If the cable is not long enough, the solution is not to extend it but to reposition the receiver.
An antenna cable is not an ordinary conductor but a line manufactured to a particular characteristic impedance. The system is matched to this impedance. Cutting the cable spoils the match; splicing it both spoils the match and creates reflection and loss at the joint.
Two effects accumulate as the length increases:
- Attenuation: there is a certain signal loss in every metre of cable, and this loss increases as the frequency rises.
- Mismatch reflection: with a joint of the wrong impedance part of the signal comes back and never reaches the antenna.
The practical order of solutions is this: first try moving the receiver to a point closer to the antenna. If that is not possible, request an original antenna solution of suitable length from the manufacturer. Avoid home-made joints and soldered splices; the joint is also the weak link for moisture ingress.
Do not route the cable around sharp corners, do not crush it with tight clamps, and do not run it parallel to power cables over long distances; make unavoidable crossings at 90 degrees.
The context in which this term is used: 433 MHz or 2.4 GHz?