Electronics Raspberry Pi

Raspberry Pi Zero 2 W external antenna mod

Modifying a Raspberry Pi Zero 2 W to add an external antenna with a U.FL RF connector

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 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 blog post and with the announcement of the new Raspberry Pi Zero 2 W version we tried to order the new board and try the same modification again.

The Raspberry Pi Zero 2 W board before modification

Initially there was very limited stock available and we were not able to order the new board until the end of November.

As with the previous version the Raspberry Pi foundation have 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 link 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 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 which goes to the PCB antenna. We used a Dremel with an engraving tip, but this 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 heat 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 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 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 vertical. The signal strength would improve further if the antenna was fitted to a metal ground plane.

The following table shows a list of networks found and their signal strength and quality readings. Most networks showed an improvement 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?

There have been several comments posted on various blogs which have asked 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 WiFi 2.4 gigahertz frequency.

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8 comments

avatar
Real Name
10 December 2021 at 6:53 pm
Great post, thanks for risking your Zero 2 W to do this mod!
avatar
Tim
13 December 2021 at 1:49 pm
Dont destroy the trace, just move the 0 ohm resistor.
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Brian
13 December 2021 at 2:09 pm
There isnt a zero ohm reisistor on the 2W mode, only on the first gen one.
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greetings from Hackaday
13 December 2021 at 2:18 pm
Cool! Do you think this could be done by removing the resistor that appears to be inline with the PCB antenna? I personally would be scared to cut the trace :)
Of course, I'm not sure if this would actually work, RF isn't really my cup of tea.
avatar
Pat
13 December 2021 at 4:14 pm
Leaving the track's worse than you think. The resonant frequency of the stub needs to be calculated in the propagation speed of the wave (on the board) not free space. It looks like CPWG, which means the effective dielectric constant's probably around 2, meaning it's probably around 70% speed of light. So it's actually more like 12 GHz, or the 5th harmonic.

But if I were doing this I'd probably scratch the trace to generate a pad so that I could rotate the resistor there if I wanted to.
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greetings from Hackaday
14 December 2021 at 12:36 am
Please disregard earlier message, and -1 to me for lack of research. I think I understand now.
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Keith
26 June 2022 at 3:35 pm
I am developing a product for a client and the heart of it is the RPi Zero 2 W (yeah, I know... real easy to source in quantity right now)

The problem I am having is the RPi constantly drops the WiFi connection all together and then brings it back and it's worse when the CPU is under heavy load. I have tried messing with WiFi power save features in rc.local and read about adjusting the Group Rekey Interval. I have tried running it off official Canakit supplies (tried the one for the RPi 4b) and I am still having it drop out. I can't have the WiFi drop out at all, it's essential to the product.

Any thoughts on if this would help not only WiFi range, but stability. If it's a firmware issue with the chip, then I doubt this will help me, but I wanted to ask and see what you thought.

Thanks for the guide!
avatar
Brian
27 June 2022 at 8:54 am
Hi Keith

We havent had any issues with the WiFi dropping but if the Pi is getting a low signal the antenna mod should improve the signal strength. This mod will invalidate the RF compliance of the board so could be an issue if you are selling them again.

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