C-ITS reaches a few hundred metres in a town and a few kilometres with a clear view. Within those limits, where you put the receiver decides almost everything — far more than which board you built. A well-placed cheap receiver beats a badly-placed good one every time.

• The higher, the better. This is the single most effective change you can make.
• Outdoors beats indoors, by a lot. Windows reflect 5.9 GHz, and coated or tinted glazing is close to a mirror at this frequency. If you must stay inside, put the node directly against a plain, untinted window facing the road.
• Line of sight is what counts. A free view towards a road, an intersection or a tram line gives the best results. A single building between you and the sender costs more than a few metres of height gain.

The enclosure exists so that the board can be mounted outdoors permanently — on a balcony, a railing or a mast.

• A 5 GHz Wi-Fi access point close by will degrade reception. 5.9 GHz sits directly next to the Wi-Fi band, and a strong neighbour desensitises the receiver's front end. Either separate the two physically, or switch the access point's 5 GHz band off. This costs you nothing on the receiver side: the official node has no Wi-Fi at all, since its radio is fully occupied with C-ITS.

If reception is poor despite a good mounting position, this is the first thing to check.

The antenna printed on the ESP32-C5-WROOM-1 module already performs very well. Do not assume that an external antenna is automatically an upgrade.

There is also a build variant using the ESP32-C5-WROOM-1U module, which has a u.FL connector for an external antenna instead. Which one to pick, and which pigtail you need, is covered under Get one.

If you do use an external antenna, polarization matters more than gain. We tested this with a Ubiquiti airMAX 16 dBi, on which horizontal and vertical polarization can be connected separately:

The test setup ran three receivers side by side: the integrated PCB antenna, the external antenna vertically polarized, and the same antenna horizontally polarized.

Comparing the reception heatmaps gives a clear ranking:

1. Vertical external antenna — best
2. PCB antenna of the ESP32-C5 — very close behind, and no extra hardware
3. Horizontal external antenna — clearly worst

Ubiquiti, vertical

ESP32-C5 PCB antenna

Ubiquiti, horizontal

The practical conclusion: unless you have a specific reason and a good antenna, keep the PCB antenna and spend the effort on mounting height instead. If you do go external, mount it vertically.

The heatmaps above come from the heatmap in the self-service portal, which is a good way to evaluate your own changes.

• A typical operating temperature is around 55 °C.
• In direct summer sunlight, more than 83 °C has been measured inside the enclosure.
• Turn the LED brightness down in the self-service portal (0 = off, 255 = maximum). At full brightness the status LEDs contribute a noticeable amount of heat inside a sealed box.
• Prefer a shaded mounting spot. North-facing, or under an eave, costs nothing and helps considerably.

The enclosure is 3D-printed, designed in OpenSCAD, and lives in the case directory of the hardware repository: its-g5-receiver/case

We recommend printing in ASA. ASA is UV-resistant without special additives, so the filament manufacturer hardly matters — we always buy the cheapest white one. PLA will not survive a summer outdoors.

For a weatherproof result you need all of it:

• The printed bottom seal (bottom.stl) and its screws (M4 × 12, TX20)
• The rubber plug for the LAN cable entry
• Cable entries facing downwards, with a drip loop before the cable enters

If the receiver is mounted outdoors and its LAN cable runs back to a switch or router indoors, plan for an Ethernet surge protector. A thunderstorm in the area induces voltage spikes on outdoor cable runs, and those spikes travel down the cable into whatever is connected at the far end.

In short: one surge protector per outdoor cable run, installed inline before the switch, and it must be grounded. Without grounding the device does nothing at all.

• Receiver outdoors, switch or router indoors → plan for a surge protector.
• Fully indoor installation, for example on a windowsill behind glass → not needed.
• A surge protector guards against induced surges from nearby lightning or static build-up. It does not protect against a direct strike — that needs a proper lightning protection concept from a professional.

Not primarily the receiver. At around 20 € it is cheap to replace, and so is a PoE injector. The money sits at the indoor end of the cable: a PoE switch costs 100 € and upwards, and an unprotected outdoor run feeding into it can destroy it. In the worst case the damage does not stop at the switch — other devices on the same network can be hit as well.

A proven option is the Ubiquiti ETH-SP-G2 (Ethernet Surge Protector, around 13 €):

• Position: inline in the outdoor run, before the switch — that is, at the indoor end of the cable, as close as possible to where it enters the building. With several outdoor runs, each run gets its own protector.
• Grounding (mandatory): connect the grounding terminal with at least 4 mm² copper wire, green/yellow, to protective earth or the equipotential bonding bar. Without grounding the surge protector is useless, because the diverted surge has nowhere to go. Buy the wire separately.
• Outdoor connectors: keep them protected in an outdoor box or under cover, with cable entries facing down and a drip loop. Connectors outside are then uncritical.