In an effort to improve zigbee performance and extend the network into my garage, I have setup 4x cc2531s with external antennas around my house.
They are between 2m and 15m apart but they continuously showing as offline and sensors and switches at the extremes of the house and garage dont connect.
I am using a raspbee II stick with ZHA and struggling to get everything working short of having a zigbee router every 2-3 metres!
I have zigbee running on ch 25 and have moved all my wifi APs to channels 1 & 6 thinking that may help.
Is there anything I am missing or could there be a compatibility issue somewhere?
Not addressing your question directly, however some info that might help from my experiments. I have both ZHA and ZIGBEE2MQTT running. However, I have moved most of my new zigbee stuff to zigbee2mqtt as I find it more adaptable. As one example that might help, I run a production zigbee2mqtt in one docker container and a 2nd test zigbee2mqtt in another docker container. Having a test zigbee network that is connected to HA via mqtt allows me to test devices and locations of them while my HA/zigbee2mqtt runs nonstop in parallel. This for the small prices of a 2nd coordinator device. You can keep your production HA /zigbee running and futz around with location of routers and devices on the test setup. You could probably do the same by just adding a test zigbee2mqtt network to your zha production, but that adds another set of variables as you move your devices from test to production.
My 2nd bit of info. I have no science to support this, but my production zigbee2mqtt network runs on channel 11 and my test zigbee2mqtt runs on channel 25, I too have my 2.4 ghz wifi shoved down to low channel numbers. Again, no science to back it, however I believe my channel 16 zigbee network is a bit more stable and robust than my channel 25 zigbee network.
Another point, you don’t go into detail on what cc2531 hardware and firmware you are using. Again from my experiments with using PTVO firmware on various real TI cc253x and clone cc253x devices. Both the quality and design of the antenna hardware setups have shown me much different signal range. Combine this with trying to figure out the proper firmware configuration for amps on the devices (especially trying to decode the clone devices) took some work until I found a firmware and hardware config that I fairly well understood.
I think this is interference from either Wifi (even you are on a different channel, however if close still a problem) or USB3 ports or a SSD disk.
like mentioned below, I would go for Zigbee channel 11 or 15 and put wifi on the higher channels. If not for anything else, then as both ZHA and Z2M use the low channels as standard.