Testing 9 external antennas with CC2531 ZigBee coordinator - NotEnoughTech
CC2531 ZigBee USB Dongle zigbee2MQTT
ITEAD of Sonoff fame now sells a very inexpensive Zigbee USB dongle that should work out-of-the-box with Home Assistant ZHA integration and Zigbee2mqtt : r/homeassistant
Extend range of zigbee network using CC2531/CC2530 routers · Issue #52 · Koenkk/zigbee2mqtt · GitHub
Are all CC2531 Router/repeater so chatty? - Get Help - Hubitat