Slow internet speed with 5th gen Time capsule and cable

In the airport utility I have only access to automatic or the channels 36, 40, 44 and 48, which are all 20 Mhz channels (when looking up wifi channels on wikipedia).

This is not true.. channels 36-48 will give you 80mhz.

It can give somewhat poorer range but if your local regulations do not permit 80mhz on DFS or higher band channels there is nothing you can do about it.. 36-48 is 80mhz.

Is the country set correctly in the wireless options area.. ??

there should be several channels available with a higher frequency (at least how I read wikipedia

You cannot select DFS channels yourself.. they are only selected by the router when set to automatic and must be restricted in the face of radar.

You also can use 149-161 but only at extremely low output. 25mW which is far less than signal allowed in US and most other countries which will be about 10x greater.

Yes.. there is another issue.

Sorry I was slow to respond and my connection dropped out.

You stated you can only get 100Mbps through the TC with wired connection.. can you please confirm that is the case..

That means the TC is faulty.. it should connect to your wall connection at gigabit.

For a long time I did not realise it is actually shown in the airport utility on iOS. The Mac version is a bit useless. There is so little detail.

If the data rate is only 100Mbps then you cannot achieve higher speeds no matter how fast the wireless is connected.

(Actually in my case this is not relevant.. because it is connected in bridge without the WAN port.. it just so happens that one LAN port has 100mbit connection.

tc5c# acp PHYS

PHYS=

0: DOWN

1: 1000 Mbps Full-Duplex

2: 1000 Mbps Full-Duplex

3: 100 Mbps Full-Duplex

This is only available if you have command access.. which is difficult.

Talk to me if you are interested. rayhav@gmail.com

If you have never done a factory reset I would give that a go.. and post the screenshots of the actual TC setup.

Use very short names.. no spaces pure alphanumerics.. same for passwords but can be longer.

The problem is not the cable.

With the Time Capsule plugged into the wall and a computer plugged by ethernet directly to the TC you should get your full 300Mbps.

but I am only able to get around 100 Mbit through the Time Capsule, and using a cable from the TC doesn't help

Please do this test again with wireless turned off in the computer.. if you cannot achieve more than 100Mbps then something is wrong with the setup.. or the patch cable used wall to WAN port of the TC.. although your other patch cable from computer to the TC must be ok if it gets 300Mbps.

There is a second problem then.. the wireless is set to only use 20mhz. I think this is due to interference on the DFS channel.

I would go to the wireless setup in the airport utility and change it over to channel 36-48.. any of those.. and make sure you get full 80mhz connection.

In addition to LaPastenague's comments a MCS Index of 8 corresponds to a maximum possible bandwidth of around 175 Mbps for a 20 MHz-wide channel in the 802.11ac radio mode. Pretty much what the drop-down menu is already telling you. This is even with very good signal quality (SNR). SNR = RSSI - Noise = -52 -(-98) = 46 dB

The bandwidth limitation, as LaPastenague has mentioned, may be due to your country's Wi-Fi band restrictions that prevent civil radio interference with military or general aviation radar systems.