Ive just purchased a Zzh stick , would a 2m extension cable “if shielded” , be too long for the Zzh stick ? my server is located next to the wifi router so ideally I would use a 2m cable minimum to get it away from the server , or should I be considering using zigbee2mqtt on a raspberry pi to get it right away from the server and router? my intention was to use ZHA.
2m should be more than enough. IIRC USB extensions start to loose data after three to five meters, that’s why there is the recommendation to use a “powered extension”, if you go up that value. Imho, 2m is ok, I wouldn’t go further, but you could easily reduce this. I’m using a 50cm extension cable, and that seems to be enough to get rid of the interferences. 
thanks for the advice, much appreciated 
I’m not sure if a 50cm cable would get the Zzh stick far enough away from the router. Currently I have the 2.4GHZ WiFi active on the router for all the esphome switches to communicate with home assistant, otherwise I would turn it off and only use 5GHZ to completely reduce the possibility of signal interference. I think I will go with 2m and hopefully that is enough. Othewise I will look at zigbee2mqtt on a raspberry pi.
The router isn’t your problem. At least normally it isn’t. The problem lies around the Pi or your server (whatever it is, a NUC or…). There are many interferences and these should be avoided.
The best example is a Pi: if you put the stick into one of the USB ports, it will “transfer” it’s sending power directly onto the Wifi antenna, the BT receiver and so on. This is the part you want to avoid.
But I’m quite sure it doesn’t hurt to get it away from all other devices. But as I said, keep in mind the longer the extension is, the sooner data will get lost.
A friend of mine is working for BMW and they had a lot of different problems regarding the USB connection from phones or other media players, that didn’t work correctly. Sometimes data was lost, sometimes they couldn’t get recognized and so on. They searched quite a while for the problem, and then one of them had an accident and they could physically see, how the USB cable was put in the car: they did run it from the place between the seats back to the trunk and then forward to the MultiMediaUnit that is located behind the radio. Turned out, it was around six to eight meters (depending on the car), and that was to much. They changed the cables entirely from between the seats directly to the MMU. A few weeks later the team was dissolved and they were given new jobs - not one problem any more.
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Wow , thank you for the explanation that really helps , I did wonder why connecting directly to the USB port caused such issues, but also for explaining why the length of the cable could also cause issues too. I went with the 2m shielded cable in the end hopefully that works a treat.
Really appreciate the advice from someone with much more knowledge and experience.
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You can use up to a 5-meter long USB extension without any problems, (remember that a Zigbee USB dongle/adapter is only using USB 2.0 and is just used for low bandwidth serial communication after all), but due to USB limitations longer than that and you need to use a cable with USB repeater or one of those set of powered USB extension cables that you use in combination with ethernet cables to get longer range.
Recommend read and follow Generic best practice tips on improving Zigbee network range and general stability · zigpy/zigpy Wiki · GitHub
In summary; interference can be a huge problem for Zigbee.
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There are 2 kinds of interferences :
- because of the “server” => Where a simple 50cm cable will solve
- WiFi : That won’t be solved by any cable… Just think your networks (WiFi & Zigbee) before you start them.
Some read about WiFi interference : ZigBee and Wi-Fi Coexistence | MetaGeek