PCB Trace vs External Antenna
The antenna is one of the component that most dramaticallyimportant affectsfactors in the range and reliability of a LoRa mesh nodenode, - more thanalongside spreading factor,factor and transmit power,power. or(Spreading evenfactor in particular changes the radiolink chip.budget Yetby it15-20+ dB across SF7-SF12, which often outweighs the few-dB difference between a poor and a good antenna.) Even so, the antenna is also the most commonly overlooked hardware detail, especially by beginners who assume the built-in PCB trace antenna is adequate for outdoor use.
PCB Trace Antennas: What They Are
A PCB trace antenna (also called a PCB antenna or on-board antenna) is a specific pattern etched directly into the copper layers of the circuit board. No separate component - it is part of the PCB itself. You can identify one by looking at a corner of the board where the copper traces form a meandered or serpentine pattern, often with a small keepout area around it where no other copper is present.
PCB trace antennas are used because they cost essentially nothing to add during PCB manufacturing, they take up minimal volume, and they eliminate the need for an SMA/U.FL connector and cable. For products designed to be small and cheap - like the Heltec V3 or many ESP32 dev boards - they make sense as a baseline.
Why PCB Antennas Are Inadequate for Outdoor Use
The theoretical gain of aA well-designeddesigned, well-matched PCB trace antenna at 915 MHz iscan approximatelyreach roughly 0 - 2 dBidBi, but the small or detuned implementations found on typical dev boards are frequently negative-gain (commonly -3 comparableto -6 dBi, sometimes worse) once electrical size, lossy FR4, ground-plane coupling, and proximity to a shorthand rubberor duck.case However,are inaccounted for. Treat a dev-board PCB antenna as significantly worse than a quarter-wave whip. In practice, PCB antennas on development boards suffer from several additional problems:
- Proximity effects: A PCB trace antenna's tuning is affected by everything near it - your hand, a battery, the case material, the board itself. Moving the device changes the antenna's effective frequency and radiation pattern.
- Orientation sensitivity: PCB trace antennas
typicallyarehavenon-omnidirectional,awithhighlypronounceddirectionalnulls in their radiation pattern. In a pocket or on a table,thea null direction may be exactly toward the nodes you want to reach. - No replaceable component: If the PCB trace antenna design is suboptimal (common on cheap dev boards), there is nothing to improve without adding an external connector.
- Body shielding: When carried in a pocket, the human body absorbs several dB of the already-weak signal from a PCB antenna. An external antenna on a cable can be positioned to avoid this.
Gain Comparison
| Antenna Type | Typical Gain | Effective Range vs PCB | Notes |
|---|---|---|---|
| PCB trace antenna (dev board) | Baseline | Subject to proximity detuning | |
| Small rubber duck (included) | 1 - 2 dBi | ~1.1 - 1.3x | Better than PCB in most orientations |
| Quality 915 MHz rubber duck | 2 - 3 dBi | ~1.3 - 1.5x | Taoglas, Linx brand options |
| Quarter-wave whip + ground plane | ~ |
~1. |
Omnidirectional; DIY- |
| Fiberglass 3 dBi (915 MHz) | 3 dBi | ~1.5 - 2x | Best for outdoor fixed nodes |
| Fiberglass 5 dBi | 5 dBi | ~2.5 - 3x | Narrower beam; use at elevation |
| Fiberglass 8 dBi | 8 dBi | ~4 - 5x | Very narrow beam; hilltop/tower |
| Yagi 10 dBi | 10 dBi | ~6 - 8x | Highly directional; point-to-point |
Range multipliers are approximate in ideal line-of-sight conditions. Real-world gains depend on terrain, obstruction, and link margin. Antenna gain figures for commercial products are nominal/marketing values and vary by sample.
Connector Types: SMA vs U.FL
SMA (SubMiniature version A)
SMA is a threaded RF connector found on most external antennas. Boards with an SMA connector (T-Beam, T-Echo, RAK WisBlock)WisBlock base boards) can directly accept standard SMA-terminated antennas. There are two variants:
- SMA: Female connector on the antenna (outer thread, inner pin) plugs into the board's male SMA jack (inner socket, outer thread)
- RP-SMA (Reverse Polarity SMA): Used on WiFi routers and many US-market devices. The genders of the center conductor are swapped. A standard SMA antenna will NOT fit an RP-SMA connector without an adapter. Make sure your antenna matches your board's connector type.
U.FL (also called IPEX or MHF1)
U.FL is a tiny snap-fit coaxial connector used internally on boards when the antenna connector needs to be on a cable or module rather than soldered to the main PCB. The Heltec V3,V3 LoRa output, some WisBlock modules, and many radio modules use U.FL.
A U.FL connector board requires a U.FL to SMA pigtail cable (typically 10 - 15 cm) to adapt to a standard SMA antenna. ThisOver such a short run of thin (1.13 mm / RG-178-class) coax, this cable introduces approximatelyonly a small fractional-dB insertion loss at 915 MHz (on the order of 0.3 - 0.5 dB of loss,dB), which is a worthwhile tradeoff for a proper external antenna.
When Is a PCB Antenna Acceptable?
PCB antennas are adequate in these specific scenarios:
- Indoor testing at short range: Verifying that firmware flashed correctly, testing basic connectivity between nodes in the same room
- High-density indoor mesh: In a building with many nodes at close range (under 50 meters), PCB antenna limitations are less relevant
- Ultra-compact wearable or embedded device: If physical size constraints prevent any external component, a PCB antenna may be the only option - but accept the range limitation
For any outdoor deployment, fixed repeater, or range-critical use, an external antenna is non-negotiable.
Antenna Selection for Common Boards
| Board | Built-in Antenna | External Connector | Recommended Upgrade |
|---|---|---|---|
| Heltec WiFi LoRa 32 V3 | U.FL / IPEX ( |
U.FL - SMA pigtail + 3 dBi rubber duck | |
| LilyGO T-Beam Supreme | None (SMA only) | SMA male | Quality 915 MHz 3 dBi rubber duck; fiberglass for fixed |
| LilyGO T-Echo | None |
U.FL / IPEX (verify; sources conflict SMA |
Included rubber duck is adequate; upgrade for repeater use |
| RAK4631 (WisBlock) | None | IPEX (U.FL) on module | RAK base board provides SMA passthrough; use 3 - 5 dBi fiberglass for fixed nodes |
| Station G2 | None | SMA male | 3 dBi stubby for portable; fiberglass for fixed |
Cable Loss Warning
If your antenna requires a coaxial cable run (for example, mounting an antenna on a roof while the radio is indoors), cable loss must be accounted for. At 915 MHz:
- RG-58: approximately 0.
67 - 0.8 dB/meter - avoid runs over 3 meters - RG-8X: approximately 0.
3527 - 0.30 dB/meter - usable up to ~10 meters - LMR-400: approximately 0.
1413 dB/meter (~3.9 dB per 100 ft) - suitable for long runs - LMR-200: approximately 0.23 - 0.25 dB/meter - good for medium runs
A 10-meter run of RG-58 costs you 6roughly 7 - 8 dB at 915 MHz - equivalentmore tothan runninga at5x onereduction quarterin the transmit power andpower, completely erasing any gain advantage from a high-gain antenna. Use the lowest-loss cable practical for your installation.