Coax Loss Tables
Edit on GitHubReference tables for coaxial cable loss at UHF, and how to budget the losses in the beacon's link.
Coax Loss Tables
Loss tables answer one question: how much signal disappears between the radio and the antenna. At 433 MHz the answer is “not much, unless the cable is long or bad”.
Loss per 10 meters at 433 MHz
| Cable | Loss / 10 m | Notes |
|---|---|---|
| RG174 | 6 - 8 dB | Thin, flexible, lossy |
| RG58 | 3.5 - 4.5 dB | Standard thin coax |
| RG213 | 2 - 2.5 dB | Thick, stiff, low loss |
| LMR-400 | 1.5 - 2 dB | Professional grade |
| LMR-195 | 3 - 4 dB | RG58-class but better shield |
What the numbers mean for a beacon
The beacon’s internal run is typically 10 - 25 cm: the loss there is 0.1 - 0.2 dB, negligible. The table only starts to matter when you:
- Mount the antenna away from the case (extended mast)
- Use a directional antenna on a pole
- Test from inside a vehicle or shelter with a long feed line
Doubling is the trap
Every 3 dB lost is half the power: +22 dBm into a cable with 3 dB loss becomes +19 dBm at the antenna. A 5 dB loss is nearly two-thirds gone. This is why the recommendation for anything beyond 1 m is a low-loss cable, not RG174.
Measuring, not trusting
Cable loss from a table is an estimate. A damaged cable (kinked, crushed, wet connector) can add many dB. Test the finished run with the two-beacon bench procedure (Two Beacon Bench Test) and compare the RSSI to expectations.
Related pages
- Antenna Cable and Connectors for the choice
- RF and Link Budget for where loss fits
- Antenna Testing and Tuning for the test procedure