How can I scan my Wifi Channels to determine the best channel for my network. That option window seems to no longer be available.

Have you looked at

Spotlight -> Wireless Diagnostics -> Window -> Utilities -> Wi-Fi Scan (tab) -> Scan Now

then look at the lower right corner?

This is from my Mavericks 10.9.5 system

NOTE: I personally do not really like to use that information. As its seems to count my own WiFi base station against me. If you want to use this service, then at least turn off your WiFi base station (and if you have extension access points, turn them off as well). Then at least you will only be measuring the signals from your neighbors, and not your own equipment.

If at all possible I try for 2.4GHz channels 1 or 11, as more times than not, many neighboring routers tend to choose 6. 1, 6 and 11 are the only 3 US channels that do not overlap, as each channel uses 5 channels worth of bandwidth (in a bell curve more or less). Channel 6 extends into 4,5,6,7,8. Channel 1 extends into (-1),(0),1,2,3. Channel 11 extends into 9,10,11,(12),(13).

For 5GHz if I can get it, I want either Channels 36 or 149. This generally tends to be easier to get, as 5GHz ranges are a bit shorter than 2.4GHz and I almost never see my neighbor's 5GHz signals. The reasons for 36 and 149, is that 5GHz protocols (especially the new 802.11ac) can automatically gang together upward adjacent channels to get more bandwidth. I think 802.11ac will gang as many as 4. This is why I try for 36 and 149.

NOTE: mostly I want the higher 5GHz bandwidth for in my home file transfers and backups between the systems in my home. My ISP speeds are easily satisfied by a single 20MHz wide 5GHz channel.

If I am away on vacation using my own portable WiFi router, I may choose an in between channel if only because I may be in a condo building with lots of competing WiFi sources. Then I look closely at the RSSI and Noise fields trying to find the best in between channel.

Channels with RSSI values in the -40's are strong signals from the neighboring condos, so I'm trying to avoid them. I'm looking for RSSI signals from the neighbor's in the -70's, -80's or -90's (weak signals). Keeping in mind that a 2.4GHz channel uses 5 channels, I do not want choose channel 2 if channel 1 has a very strong signal. I'm hoping to find adjacent channels that are weak and then pick an in between channel with no competition or a very weak signal so that the adjacent channel overlap will not be very strong.

With respect to noise, I want numbers in the -90's as that is very low noise. Whatever channel I choose, when my router is using that channel I really ONLY want to see noise in the -90's. If I cannot get that, then -80, etc... But the more noise the more likely I'm not going to get good data transfers.

Noise and low RSSI signal strength can come from adjacent channels with strong signals. Noise can also come from Microwave ovens (they made 2.4GHz available for WiFi for a reason; it is the wavelength that water vibrates, which is how Microwave ovens work, and also high humidity can reduce the range of a 2.4GHz signal), 2.4GHz cordless phones (yours or your neighbors), 2.4GHz baby monitors (again yours, or your neighbors, and these are the worse, as they are always operating), metal appliances (a refrigerator if in line of sight to the base station will reduce signal strength), metal wall studs (something that is being used in a lot more new construction), concrete walls with metal re-bar (as well as floors and ceilings in some multi-level appartments/condos).

Thank you Bob. This is excellent and precise info.

Cheers! 🙂

-Scott