I have a wireless network set up at home via Time Capsule. I also have Time Machine installed on two laptops and they backup to the Time Capsule. I have noticed that whenever a backup is running the wireless connection speed drops from 30Mbps to around 8Mbps or less. Is this normal and is there a way to minimise such drops?
Any WiFi has a bandwidth.
That is the maximum amount of data it can handle.
For example the 5 GHz WiFi can handle up to 8x more data then the 2.5 GHz.
Setting (limiting) a bandwidth usage for a specific application is not easy and Mac does not offer a build in solution, but there might be some external applications for that.
Here are some suggestions how to do that.
However, one can also use the AirPort Utility (in your utility folder) to set the Date/Times for Time Capsule. Set it to Times when you are not using the computer to prevent overcrowding your WiFi network.
I had the same problem (and even disappearing network). I found reports that the Airport Extreme and Time Capsule devices don't handle mixed IPv4/6 environments very well. Switching off one (in my case, the latter), was said to address the problem.
After I switched it off, sadly and oddly, my problems disappeared.