The wi-fi on two computers was giving different performance. I wondered if this was because it was using a different frequency wi-fi. I found this article useful on wi-fi. It says the higher the frequency used, the better the performance.
Display information about what the wi-fi is currently using.
The iwconfig command gave
wlp4s0 IEEE 802.11 ESSID:"BTHub6-78RQ" Mode:Managed Frequency:5.24 GHz Access Point: 94:6A:B0:85:54:AA Bit Rate=585.1 Mb/s Tx-Power=20 dBm Retry short limit:7 RTS thr:off Fragment thr:off Power Management:on Link Quality=41/70 Signal level=-69 dBm Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0 Tx excessive retries:0 Invalid misc:32 Missed beacon:0
Which shows the frequency (5.24 GHz) and bit rate (585.1 Mega bits /second (not bytes).
On the slower computer on the same wi-fi network it had 2.412 GHz.
Display information about the wireless interface
The iwlist command displays information about the wireless interface and its capabilities
iwlist wlp4s0 frequency gave
wlp4s0 32 channels in total; available frequencies : Channel 01 : 2.412 GHz Channel 02 : 2.417 GHz Channel 03 : 2.422 GHz ... Channel 48 : 5.24 GHz ... Channel 132 : 5.66 GHz Channel 136 : 5.68 GHz Channel 140 : 5.7 GHz Current Frequency:5.24 GHz (Channel 48)
On my other machine it only listed 2.412 to 2,484 GHz.
What frequency is available?
Displaying my BT hub (http://192.168.1.254/basic) it displayed 2.4 and 5 GHz and channels 1 and 48. Thus I can use frequencies 2.412 and 5.24 GHz
Change the frequency being used
sudo iwconfig wlp4s0 freq 2.412G
Turn wi-fi off and on – and it picks up the changed value.