Wifi interference from Direct-Roku?

Our network (primary and guest) is generated by a Time Capsule (802.11 ac, 2.4 and 5Ghz) and extended by a 4th generation Time Capsule (802.11n, 2.4 and 5), but is in a fairly busy area (about 15-30 SSIDs are visible at all times) and drops or slows frequently.

With that many nearby Wi-Fis it may be very difficult, for any manufacturer's wireless access point, not just the the AirPort base stations, to find a "clear" channel that they would not be interfered with. It would typically require using an all-wired solution, not something you were hoping for.

Running wireless diagnostics identifies a County Code error (and of course channel congestion). When I scan the visible SSIDs, only one shows a non-US country code. This is the Direct-Roku signal (listed as country code Q2) and is fairly strong.

... and country code Q2 would be New Zealand. Direct-Roku is a peer-to-peer Wi-Fi network that allows the Roku and its remote to directly communicate on. It is based on Wi-Fi Direct, which can operate on 802.11a/g/n networks ... meaning both the 2.4 & 5 GHz bands. Not 100% sure which band the Roku devices operate on.

Without lining my home in aluminum foil, do I have any recourse?

Unfortunately, not much. If you know your neighbors well, you could try to discuss the issue with them. However, even if they are willing to help, they are, most likely, experiencing the same issues as you. Again, all wired connections will definitely resolve this.

I have read about setting up a dummy network with an old router to avoid 802.11d issues in crowded areas. Would this work with a direct wi-fi signal? Wouldn't it just cause more channel congestion?

... and more congestion is all that will introduce and not a recommended solution.

What channel is the Roku device using? It's likely going to be a 2.4 GHz channel, since 5 GHz signals will rarely get much further than the outside walls of a home.

If the Roku is broadcasting a 2.4 GHz signal on Channel 12 or 13, those channels can only be used with low power signals to be legal in the U.S.. If you are picking up channel 12 or 13, the device may not be low power, so it may technically be in violation of broadcast rules in the U.S., and you might have some recourse if that is the case.

Otherwise, about all that you can do is enable the option to assign a separate SSID for the 5 GHz signal on your Time Capsule(s) and run as many devices as you can using 5 GHz......since interference issues are almost always on the 2.4 GHz band.

Would the country code matter if the channel is a US-approved one?

No

So I figure that I will have to power-cycle frequently to force the router to reselect a new channel (and because the congestion seems to be dynamic regardless of location) until I can either get a wired network or move the router more centrally.

Correct

Is there a hidden "refresh" way to be able to do this easily from a phone or laptop without having to dig for the reset button on the actual router?

You would not use the reset button for this. Either pull the power cord from the back of the router for a few seconds and then plug it back in, or use the Restart command in AirPort Utility on your Mac or iOS device, if you don't want to pull the power cord and then plug it back in to restart the router.

Click on the image below to enlarge, if needed.

If you want to use AirPort Utility on an iPhone or iPad.....

Tap to open the App

Tap on the picture of the AirPort

Tap Edit

Tap Advanced

Scroll down and tap on Restart Base Station

Isn't it illegal/FCC violation to use a non-US channel?

Looks like Bob has already responded to this. Wi-Fi devices, designed to work in New Zealand, can operate on channels 1-13. Of course, as you know, in the US would be limited to 1-11. In theory, the Roku-Direct network should be operating at a very low power ... but since you can "see" this network, maybe not so low.

Assuming I can't find my neighbor, what is the quickest way to reset the channels on the time capsules if this is to be a frequent event?

With the 802.11ac base station, you can change the 2.4 GHz band channels. In theory, you can change those on the 5 GHz band, but they won't "stick." What channel you change to will depend on the channels that are operating nearby with the strongest signal level. Even though there are 11 channels to choose from, you basically only have 3 that don't overlap ... 1, 6, or 11.

Channels 12 and 13, although not normally used in the U.S. are technically legal, but they must be low power. If you "see" a signal using Channel 12 or 13, then it is likely not using low power.

I said above that if you find this to be the case, then you might have some legal recourse.....with the FCC....if you cannot find the source of the broadcast, or the owner is unwilling to make any changes.

You can probably configure the router to use a single channel if you can decide on which works best for you.

For the past 2 years before I gave up and sold my soul to the dark ones of the local DSL service I use a wireless ISP. I had gotten into the routine of every few weeks printing off half a dozen flyers and going around to the apartment buildings across the street between me and my ISP's node and begging them to try not to use channel 6. It mostly worked until about 3 months ago when the dark ones (CenturyLink, Xfinity and Direct-Roku) started pushing 40 Mbps Internet plus home cable service where you stream TV to multiple sets in a house. Then I'd get blocked for hours at a time . A few minutes here and there was okay for my web use but 3 hours nothing several times a day everyday? I gave up. Now my Internet service is going from $150/year to $400.

Yes, everybody is going wireless crazy, not helped by Apple trying to cut the cord left right and center and promoting wireless video streaming to devices. We were forced to abandon our old ISP and go for one 3x the price because there's been a blossoming of wi-fi use in our neighborhood, and we'd get blocked for hours at a time by people streaming. The last time I checked wifi (I am now all wired) I could see about 50 stations on my wifi antenna. 😝 That's not much wiggle space when you consider there are only 3 unique channels in the 2.4 GHz range.