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Updated FAQs (markdown)

Bill Zimmerman 2020-01-02 08:38:57 -08:00
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FAQs.md

@ -294,8 +294,7 @@ Choosing the AC wireless mode will populate the supported 5 GHz channels for you
![](https://i.imgur.com/ZAxB8Wf.png)
**Long answer:** AC support is not simply a function of the RPi 3B+/4's hardware capabilities. It must also take into account regulatory restrictions of the wireless spectrum. The regulatory info for brcmfmac, the kernel driver that supports the Broadcom wireless chipset, is embedded in the firmware. There are lots of [international issues with Wifi](https://en.wikipedia.org/wiki/List_of_WLAN_channels#5_GHz_or_5.8_GHz_(802.11a/h/j/n/ac/ax)) that restrict channel use, transmission power, etc. on a per-country basis. As a result, only combinations of certain frequencies (channels) and countries are capable of hosting an AC access point with the RPi's wireless adapter.
**Longer answer:** AC support is not simply a function of the RPi 3B+/4's hardware capabilities. It must also take into account regulatory restrictions of the wireless spectrum. The regulatory info for brcmfmac, the kernel driver that supports the Broadcom wireless chipset, is embedded in the firmware. There are lots of [international issues with WiFi](https://en.wikipedia.org/wiki/List_of_WLAN_channels#5_GHz_or_5.8_GHz_(802.11a/h/j/n/ac/ax)) that restrict channel use, transmission power, etc. on a regional and per-country basis. As a result, only combinations of certain frequencies (channels) and countries are capable of hosting an AC access point with the RPi's wireless adapter.
If the country configured on your RPi does not allow use of a particular segment of the 5 GHz wireless spectrum, an AC configured AP will fail to start. Errors like these are common:
@ -307,7 +306,6 @@ hostapd: Could not set channel for kernel driver
In testing, stable AP's on the RPi's supported AC channels were only reliably obtained with 'US' as the regulatory domain. To get a list of the supported channels on your RPi for the 2.4 and 5 GHz bands, use `iw phy phy0 channels`. Refer to [this issue](https://github.com/billz/raspap-webgui/issues/450#issuecomment-569343686).
### <a name="wificountries"></a>I think my country allows 5 GHz AP channels. Can I test this?
Yes, you can. In the spirit of experimentation and discovery, this project makes it easy to override RaspAP's [default configuration](https://github.com/billz/raspap-webgui/wiki/Reporting-issues#default-settings). The file [wireless.json](https://github.com/billz/raspap-webgui/blob/master/config/wireless.json) contains the regulatory domains and channels for the 2.4 and 5 GHz bands. Add a valid ISO Alpha-2 country code to the list of `5Ghz_max48ch` countries and save the file. Next, edit `includes/config.php` and add the same country to this constant:
```
@ -320,7 +318,6 @@ The **Configure hotspot** page will now let you select AC as a wireless mode opt
**Note:** it is recommended to monitor logs such as `dmesg` and the hostapd error log (available in the **Logfile output** tab of RaspAP) while doing this. Bug reports like "AC doesn't work" and/or troubleshooting requests will not be considered. No hard feelings.
### <a name="wirelessn"></a>Why is the maximum throughput of my 802.11n AP reduced by half?
In order to achieve optimal throughput with 802.11n, the wireless stream must operate at a 40 MHz wide channel on the 2.4 GHz band. A 20 MHz channel will restrict you to 72 Mbps. Your `hostapd.conf` might have the required settings, but this is no guarantee of a 40 MHz channel.
In practice, this can be quite difficult due to interference on the 2.4 GHz band. There are many things that will cause an AP to fallback to 20 MHz. The most common reason is if an AP detects another wireless network within 40 MHz, i.e. two channels, of its own channel. For example, if an AP is set to channel 6, another network operating anywhere from channel 4 to 8 will trigger a fallback. hostapd will usually report a fallback like so: