Coaxial Cable Loss
Coaxial cable produces a certain loss per metre while carrying RF power, and that loss increases with frequency. Reported values are approximately 0.44 dB/m for RG58 around 450 MHz and approximately 0.55 dB/m for RG174 around 400 MHz. Five metres of RG58 at 433 MHz means roughly 2.2 dB, that is roughly a quarter of the range.
The loss appears at the same rate in both transmission and reception; extending the cable takes a cut out of the link budget at both ends.
- Cable diameter is decisive: RG174 is thin and easy to route, but it loses more per metre than RG58.
- The frequency effect is large: the same cable loses noticeably more at 2.4 GHz than at sub-GHz.
- Connectors add up: every transition point takes its own share, and an oxidised connector increases this markedly.
This is why the decision to extend the antenna is a trade-off: taking the antenna out of the enclosure gains tens of dB, while needlessly long cable takes part of that gain back. The practical approach is to move the antenna the shortest distance that clears the obstacles, and to shorten the excess cable rather than coil it. Coiling excess cable like a bobbin can also produce common-mode problems.
Context in which this term is used: Wireless remote control installation: pairing, relay, safety