slow wifi after wake from sleep

It appears that while I am not using the 2.4Ghz radio, it is still gaining interference from the USB hub and messing up the Wifi connection in general (GG USB and Wifi standards for collision in frequencies used!). The more things I have plugged into the USB hub the quicker the connection degrades.

I am unable to disable the 2.4Ghz radio on my router entirely (my printer needs that band) so I have changed my desk layout around to increase the distance between the iMac and the USB hub a bit. So far the Tx speed has been a little more stable but if the problem persists I'll run an ethernet cable under the house and turn WiFi off entirely.

Chris

Well I had thought it was solved, but no. Since safe mode was so slow on screen rendering, I rebooted and it's been fine for a few days, but it just happened again.

I don't use the bluetooth keyboard or mouse plugged into a USB hub (externally powered) plugged into the back of the iMac. I have 2 external USB 3 drives also plugged into the back, as well as speakers. Occasionally a headset plugged into the hub.

All this worked fine on my MBP, including with everything going via the USB hub and that plugged into my iMac. There's no room on the desk to move the drives anywhere other than to the left of the iMac instead of the right.

Router is configured for 2.4GHz/5Ghz sharing same network. I can't find channel width settings, but both computers are connecting on 5Ghz ac band with 80Mhz channel width, MBP on channel 44, iMac on 153 (No auto settings for 5Ghz band). Although it is set for DHCP both computers have reserved IPs.

So far, iPad Pro, late 2013 MBP (Mojave), iPhone 7+ all work without issues. Just the iMac on Catalina.

I appreciate the suggestions so far.

Diagnostics found no errors, however with only my keyboard and mouse plugged in to the iMac directly, WiFi tx speed dropped to single digits again this morning, without even a sleep/wake cycle.

I guess the next step is to downgrade to Mojave and try again?

Allen A wrote:

First, take a look at the information here and give those steps a try: If your Mac doesn't connect to the Internet over Wi-Fi.

not the issue - I can connect, it’s that the actual WiFi speed is absurdly slow (not my internet speed)

You may also want to start up in safe mode to see if the issue persists in safe mode: Use safe mode to isolate issues with your Mac.

Trying that now. Overall system performance is lousy in this mode. Everything is slow to respond initially. Screen redraws are clunky. WiFi Tx speed is ok for now.

test the issue in another user account: How to test an issue in another user account on your Mac.

switched to a different account while it was happening and it persisted.

Overall the problem has been inconsistent. Sometimes it happens every time after wake, other times it’s good. Today it happened after wake, and then an hour later after turning WiFi off and on. At the same time my old laptop running Mojave has no issues. I also have reserved IP addresses for both computers in my router.