Adding an external antenna to the PicoMEM Pi Pico W
Overview
Background
The PicoMEM is a versatile 8-bit ISA expansion card that brings modern features to classic systems like the IBM 5150. I use it for hard and floppy disk emulation, but I was especially excited about its Wi-Fi capabilities. Until I hit a snag: poor signal strength. The IBM 5150’s steel enclosure blocks most 2.4GHz Wi-Fi signals, making reliable connectivity a challenge.
Raspberry Pi Pico W
At the core of PicoMEM is the Raspberry Pi Pico W, which features built-in Wi-Fi via the Infineon CYW4343 chip and a PCB antenna designed by ABRACON (formerly ProAnt).
Here is a schematic of the built in antenna:
According to the schematic, removing resistor R86 (0 Ohm) disables the onboard antenna, allowing you to connect an external one.
External antenna selection
I picked up a 3dBi antenna with a 17cm pigtail for just $2 on AliExpress. Its thin coax cable was ideal for the tiny pads on the Pico W. I didn't care about the PCB side connector as I was going to cut it off anyway. I recommend not choosing an antenna with a gain higher than 3dBi, as this could result in exceeding the legal output power limits in your country. I was unable to find the official design specifications for the stock ABRACON antenna, but similar ABRACON PCB antennas have gains ranging from 2.5 to 4.7 dBi.
Modifications
Note: These pads are extremely small. Only attempt this mod if you have steady hands, magnification, and solid soldering skills.
I carefully removed R86 from the board. With the resistor gone, the solder points for the antenna were clearly visible.
I started by soldering the coax shield wire to a nearby ground pad to anchor the pigtail and reduce stress on the R86 pad. I used kapton tape to help secure the cable to the PCB, minimizing the risk of accidental pad damage. Finally, I soldered the coax inner conductor to the R86 pad closest to the Wi-Fi can.
Here is a view of the completed mod:
Results
Before the modification, my Wi-Fi signal hovered around -81dBm, resulting in unreliable connections and frequent DHCP failures. After installing the external antenna, signal strength improved dramatically to -52dBm. DHCP now works flawlessly, and I can connect to retro telnet BBSes without issue.
