Antenna Cable and Connectors
Edit on GitHubCoaxial cable and RF connectors for the beacon: SMA vs RP-SMA, coax loss at 433 MHz, and the right cable for the job.
Antenna Cable and Connectors
Between the radio module and the antenna sit a connector and (sometimes) a cable. At 433 MHz this pair is forgiving, but only if the basics are right.
SMA and RP-SMA
- SMA: the pin is on the plug (male) and the socket on the jack (female).
- RP-SMA (reverse polarity): the pin is on the jack. RP-SMA exists to defeat amateur antenna swapping on consumer gear.
The beacon uses standard SMA. Check any store-bought antenna before buying: a surprising number of “SMA” antennas on marketplaces are RP-SMA, and they will not mate properly.
Coax at 433 MHz
| Cable | Loss per meter at 433 MHz | Use |
|---|---|---|
| RG174 | ~0.6 - 0.8 dB | Short internal jumpers only |
| RG58 | ~0.4 dB | External runs up to a few meters |
| LMR-195 / RG316 | ~0.3 - 0.4 dB | Good all-rounder |
The rule of thumb: for runs under 30 cm, any cable works. For every additional meter, prefer the lower-loss cable. A beacon with a 1 m RG174 run loses 0.6 - 0.8 dB, which is real but rarely fatal.
Soldering the connector
The common failure is a cold joint on the center pin or a stray whisker shorting center to shield. After soldering:
- Measure continuity center-to-center and shield-to-shield.
- Measure that center does NOT connect to shield (multimeter beep test).
- Give the cable one flex cycle and repeat.
The pigtail trap
Buying an “antenna with pigtail” is convenient, but every extra connector pair costs ~0.1 - 0.2 dB and adds a failure point. Prefer the antenna that matches the mount directly.
Related pages
- Antenna Mounting for the mount
- Wire and Connectors for the non-RF wiring
- Antenna Testing and Tuning for verifying the finished assembly