Let me just note that although it is theoretically possible to attach an external antenna to a Pixelblaze 2 or 3, I highly recommend not doing it.
I tried on another IoT ESP8266 device a few years ago. It’s terribly easy to ruin the antenna traces - I killed two “practice” boards trying to attach the coax cable - and in end, the resulting gain was, at least in my case, minimal. (Though this was possibly due to the length of the antenna cable. There’s signal loss there too.)