Adding External Wifi / Bluetooth Antenna

All ESP modules by Espressif have an incorporated trace-antenna that can be barely observed on the surface of the module. Some ESP modules have an RP-SMA connector in order to be able to connect an external antenna, such as the ESP8266, yet most others do not. Intuitively, one would want to pull an external antenna port for the purpose of amplifying the signal. For example, a Sunhans amplifier has been used before in a different project in order to extend the range of a Bluetooth dongle and quite successfully so.

The first step is to use a scalpel, cutter, or a very sharp knife to scratch the paint off the antenna traces. There should be two exposed points by default and they correspond to ground and signal.

Determining which is which is fairly simple; one of the antenna traces should be connected to the ground, such that testing for continuity between the traces and, say, the top shield of the ESP module should reveal a connection that will not apply for the other trace.

It is important to cut between the two lines and ensure that the vertical bars are not connected together, nor to the rest of the antenna on the board. After that, the traces can be tinned using a solder iron to ensure that a strong contact will be made when an antenna is connected.

Unfortunately, SMA connectors are tough to come across and most of the time the antenna cables are delivered with a connected cable. In turn, the cable itself is far from being out of copper, even though the SMA antenna cables are advertised like that, and the cable itself is brittle and can be torn easily. For that reason, it was decided to just reverse-engineer a SMA connector by cutting the connector and exposing the interior signal pin.

With the signal pin exposed, some sanding is performed to provide an uniform surface, as well as to provide enough room to be able to solder a cable onto the central pin. Now that the provided cable does not have to be used anymore, true copper wire can be used.

The final result is nice and the antenna is not yet connected because it will be soldered once the SMA connector is mounted into a case. In any case, the solution is rather pretty and allows the signal to be post-processed from the ESP in order to amplify it or alter it for other purposes. The built-in antenna should provide some range, but not nearly enough and, ultimately, the signal strength is more of a game of numbers and amplification rather than quality.