The Raspberry Pi Zero 2 W is the latest board in the Raspberry Pi Zero family, with a 1GHz quad-core processor and 512MB SDRAM and was released on the 28th of October 2021.

When the Raspberry Pi Zero W was released in 2017, we modified the board with an external antenna connector, which was a very popular post. With the announcement of the new Raspberry Pi Zero 2 W version, we tried to order the new board and make the same modification again.

Board before modification
The Raspberry Pi Zero 2 W board before modification

Initially, the very limited stock was available, and we could not order the new board until the end of November.

As with the previous version, the Raspberry Pi foundation has left a PCB footprint and jumper pads for a U.FL RF connector to use with an external antenna, but the new Raspberry Pi Zero 2 W has a solid PCB trance going to the built-in antenna compared to the 0201 links used on the previous board.

The PCB antenna and U.FL connector pads
The PCB antenna and U.FL connector pads

We ordered a suitable Wi-Fi antenna, U.FL connector and a short coaxial cable assembly from Farnell.

The parts ordered are Swivel Type Antenna, U.FL-R-SMT-1 and JF1R6-CR3-4I - RF / Coaxial Cable Assembly.

New antenna, cable and connector
New antenna, cable and connector

Before starting the modification, we used the following command to obtain a list of available Wi-Fi networks and their signal strengths and save it to a text file.

sudo iwlist wlan0 scan | egrep "Cell|ESSID|Signal|Rates" > scanlist.txt

Adding the U.FL connector

First, we need to cut the track to the PCB antenna. We used a Dremel with an engraving tip, which could also be cut using a sharp knife to scrape away the copper trance. Take care not to cut either side of the track into the ground plane; otherwise, you could cause a short circuit on the antenna circuit. We cleaned the resulting dust away with a cotton swab.

Removing the PCB track
Removing the PCB track

Next, we applied solder to the centre pad for the U.FL connector and to the two small pads to fit a zero-ohm resistor (0201 size 0.6mm x 0.3mm). We did not have a suitable 0201 resistor, so we later created a solder bridge with the soldering iron and a small amount of solder.

Applying solder to the pads
Applying solder to the pads

The U.FL connector was then fitted in place and held with tweezers, and the heat was applied using a needle-tip soldering iron to heat the centre pad.

Fitting the new U.FL connector
Fitting the new U.FL connector

The outer pads are then soldered to the ground plane on the PCB. We tried this with the small soldering iron tip but found that it did not have enough thermal mass to heat the board, so we changed it to a 2mm soldering iron tip to heat and flow the solder fully.

Soldering the connector
Soldering the connector

With the connector fitted and the solder link complete, we cleaned the area with a cotton swab and alcohol to remove any solder flux.

Connector fitted
Connector fitted

Testing the new antenna

To test the new external antenna compared to the built-in PCB antenna, we used the following command to scan for available Wi-Fi networks and saved it to a new text file.

sudo iwlist wlan0 scan | egrep "Cell|ESSID|Signal|Rates" > scanlist-result.txt

The testing was performed in the same location as before, with the new antenna held vertically. The signal strength would improve further if the antenna were fitted to a metal ground plane.

The following table shows a list of networks found and their signal strength and quality readings. Most networks improved with the new external antenna, and our home network had a much greater signal strength.

A smaller Signal Level (dBm) is better.

Network Internal Antenna Quality Internal Antenna Signal Level (dBm) External Antenna Quality External Antenna Signal Level (dBm)
Home Network 36/70 -74 dBm 44/70 -66 dBm
Nearby Network 1 24/70 -86 dBm 33/70 -77 dBm
Nearby Network 2 25/70 -85 dBm 29/70 -81 dBm
Nearby Network 3 25/70 -85 dBm 29/70 -81 dBm

With the PCB antenna, the Raspberry Pi Zero 2 W detected 4 available Wi-Fi networks. After installing the new external antenna, it detected 14 Wi-Fi networks.

The board with U.FL connector fitted
The board with U.FL connector fitted.

The video below shows the modification being made to the Raspberry Pi.

Why not leave the track and remove the component on the antenna?

Several comments have been posted on various blogs asking why we didn’t just remove the first “resistor” on the antenna trace. The component is a capacitor which measures 6.5pF on an LCR meter and is part of the tuned PCB antenna.

Removing the capacitor would create an unmatched impedance to the RF driver, which could cause problems with the signal integrity.

The small curved track, which would be left on the PCB, measures approx. 4.3mm which would be resonant at 17.4GHz at quarter wave (7th harmonic), 34GHz at half wave (14th harmonic) and 69.7GHz at full wavelength (29th harmonic). Harmonics are calculated on Wi-Fi 2.4 gigahertz frequency.