The installer says 'add an external antenna, better signal', +$11. You hesitate: doesn't the built-in say 5dBi? Don't guess — look at the hard metric, RSRP.
Gain isn't 'higher is better' — it's 'cover the deficit'
Gain (dBi) only says 'where and how hard the signal is focused' — it creates none. Built-in 5dBi is fine by the window; but two walls and 2km from the tower is a 15dB deficit that 5dBi can't cover, and only a high-gain external (9-12dBi) helps then.
Feeder loss: the hidden tax of external antennas
- SMA feeder loses ~0.3-0.6dB/m; a 3m cable eats 1-2dBi, so a low-gain antenna on a long cable is worse than built-in.
- A high-gain directional must point at the tower — 30° off and you lose half the gain.
- Know SMA (male threads) vs RP-SMA (center pin); wrong one won't mate.
Built-in enough? The RSRP line
- RSRP >= -85dBm: built-in is solid, don't waste money.
- -85 ~ -100dBm: depends on distance; within one wall, tolerable, else go external.
- < -100dBm: external directional is mandatory + shortest feeder possible, aimed at the tower.
An antenna is a tool to cover signal deficit, not a 'bigger = fancier' decoration.
FAQ
How to choose 4G CPE antennas and ports?
External high-gain antennas improve weak-signal areas; check LAN port count, PoE, SIM slot.
Single-SIM or dual-SIM (failover) CPE?
Dual-SIM standby auto-switches when the primary fails; most cases single-SIM suffices, dual for redundancy.
What is PoE on a 4G CPE for?
One cable carries data and power—no separate PSU; ideal for ceiling/outdoor installs.
Is the max-device count (client capacity) usually overstated?
Look at concurrent connections and real throughput, not the advertised max clients.