An external Wi-Fi and Bluetooth antenna adds an entirely new dimension to Raspberry Pi, especially when diagnosing wireless Wi-Fi and Bluetooth networks with Kali Linux. Raspberry Pi 4 and 5 both have the same Wi-Fi and Bluetooth module implementation thus the same procedure may be used. Mounting an external antenna in Raspberry Pi 3 is even easier. The Wi-Fi and Bluetooth module on Raspberry Pi 4 and 5 is located at the upper left corner on the top side of the board, next to a 40-pin extension port. Though it is not immediately clear how the external antenna should be implemented, looking at Raspberry Pi compute module 4 printed circuit board with a similar Wi-Fi and Bluetooth module placement reveals an easy solution. The antenna output line is connected to a small antenna multiplexer chip that can either select internal or external antenna. The external antenna must be connected to a small female connector on the printed circuit board. Raspberry Pi 4 and 5 don' t have this switch, neither they have a female antenna connector, but latter may be added and firmly connected to the Wi-Fi and Bluetooth module antenna signal line. If observed closely through a microscope or a magnifying glass, a small curved antenna signal line can be seen exiting the module metal shielding. The line is directly connected to a printed circuit board antenna consisting of four small surface mounted elements, which are arranged in two series of two elements. There is also a mysterious contact on the antenna line a few millimeters from the metal shielding. Adjacent to this contact is another small contact that connects to a much bigger contact via a short line in the printed circuit board. It is not immediately clear what this contact should do, but it you disregard the green protective cover on the printed circuit board the situation quickly becomes obvious. A small surface mounted antenna female connector can be added by scratching a little bit of green protective cover from the pads left and right from the previously observed antenna contact. Three contacts are needed to hold the antenna connector firmly in place. Having a previous bad experience with soldering miniature antenna connectors, I rather decided to directly solder a miniature antenna wire connected to an external antenna connector. But before that two more things had to be done. First, the fore mentioned contact on the antennal line and the adjacent contact had to be connected by a small piece of wrapping wire and the antenna line had to be cut to disconnect the inbuilt antenna in the printed circuit board. I also had to scratch the green insulation to make a ground antenna contact. Lastly, I connected the cable. Checking the new antenna connections with an ohmmeter and later by Raspberry Pi OS went smoothly. Next, I had to drill a whole into the aluminum casing to mount the external antenna connector. How it works? Perfectly! The Wi-Fi and Bluetooth signals are much stronger and also a long range directed antenna can be used without an external Wi-Fi adapter. How about mounting an external antenna to a Raspberry 3? You first have to look at the bottom side of the printed circuit board, next to the micro SD card socket. The Wi-Fi and Bluetooth module has no protective shielding, but there is a zero-ohm resistor to switch between the antenna connector and inbuilt printed circuit board antenna. A female antenna connector should be added and the zero-ohm resistor should be moved to the external antenna position. However, it is sometimes easier to simply remove the miniature zero-ohm resistor and rather use a small piece of wire, which I did.
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