@Chucktin 

No there is not such a feature that I am aware of.  However you could use a WiFi Analyzer app like Apple's AirPort Utility to find this information.  If you have an iPhone you can use this app, then tap on the Wi-Fi Scan button then Scan.  It will displace the channel and signal strength of all networks in the area.  just look for your SSID and read the data below the name.  

@Carl Anything in an Android app?

@Chucktin I can't really say because i don't personally use Android, at least not in the past decade.  I do know that there are several options in Android for a Wi-Fi Anaylzer I just can't say which ones are the best.  

@Chucktin 

Can you clear up for me what exactly you are looking to log?  The Subject says "WiFi signal monitoring", and in the details you mention logging the Internet signal coming from the ISP into your router. 

The reply threads so far have focused on the in-house Deco Wi-Fi signal monitoring.

Yes there are two different Android Apps that I professionally use to monitor in-house Wi-Fi. 

1.) "Wifi Analyzer", ver 3.11.2, Author Kevin Yuan, Available on the Android App Store. 

        I use this to verify SSID signal strength and Wi-Fi Channel.

2.) "Wi-Fi SweetSpots", ver 2.3.6, Product of ASSIA Inc., Available on the Android App Store.

        I use this to observe how Wi-Fi connection speed fluctuates and locate the fastest and slowest locations in a room or in the building. 

Now if you are hoping to monitor the Internet bandwidth supplied by your ISP, then you have a two options.

1.) The most accurate would be to use the Deco App supplied tool "Test Internet Speed". It is included on the Deco M5 and P7 models, not sure about the X20 model. On the M5 & P7 models, it is located in "More". It directly tests the Upload and download speed as supplied to your Deco device, which I assume is being fed through your Spectrum modem.

2.) The next best would be using a Computer connected via a wired Ethernet cable.  Use an Internet speed test like "Speedof.me" or OOKLA "Speedtest.net". 

The web based tests are manually run test and will not be as accurate as the one performed by the primary Deco node, because all devices on your in-home network will be consuming some amount of your available internal Internet capacity. Testing from a connected Computer in-home will show what is remaining, after any other devices in your home use their part of the available bandwidth from the ISP. If you have many IOT devices like security cameras, Smart Home devices such as Google Home, Ring, Amazon Echo, Roku, Android, etc & other Cell Phones, Tablets and Computers connected to your in-home network, then the remaining Internet bandwidth may shock you.  I have seen homes with 75Mbps supplied from the ISP and after 20-30 in-home IOT devices and other Smart connected devices, the remaining available bandwidth was down to 18Mbps. 

However; If you want to continuously monitor your ISP's available bandwidth then you will need to download a tool to run on your Ethernet connected computer.  There are a myriad of non-free choices and a very few Free choices.  Search with your browser for "continuous internet speed test". Some even send you alerts in addition to continual logging.

       One example would be http://startrinity.com/InternetQuality/ContinuousBandwidthTester.aspx 

Best of luck. 

@DAServices 

Thank you - that is the type of answer I was looking for.

Perhaps I'm mis-informed? My understanding is that the the Internet feed from our ISP, Spectrum, is a portion of the signal supplied to the Cable Modem and the Cable Modem seperates that signal (the WAN) out to pass it on to our Home Router. As far as I can tell our present Home Router, a LinkSys EA9300, is not the problem and operates without a hitch. The only reason I picked up the X20 was to get the Mesh setup as the house is a spread out "L" and there are outside walls between the central location and the ends where our computers, TVs, tablets, etc are installed and operate regularly. It did not occur to me that their would be a difference between monitoring the signal before (incoming) and after (ouput) the Router.

Spectrum's service calls are responsive enough but I suspect (I do not _know_) that they are dealing with less than adequate original hardware (pre 1990s) in this subdivision, What I'm hoping to do is to provide a log of service drop-outs to Spectrum that will bolster my arguement that we (here at this house) need a new underground cable and that Spectrum should update whatever switches are feeding the nodes here as they are not keeping up with the service load.

cvt

@Chucktin 

Use the Speed test function of your LinkSys EA9300 router, to verify and track the Spectrum Link speed.  

Since you are unable to cover the entire home with the Wi-Fi from the Linksys, I would suggest that you turn off the LinkSys Wi-Fi and use the TP-Link Deco in AP mode. Plug the main node into an ethernet port on the LinkSys EA9300. 

Then only use the TP-Link Deco Wi-Fi, to create the mesh around your home.  Use the two Apps that I listed to confirm the best placement for the additional Deco Satellite node(s), unless of course if you are using wired Ethernet as backhaul :-).  If you do use the Wi-Fi as backhaul for other cheaper satellite nodes, you will see the signal dropping to near 55Dbm and that is where you place the next ancillary Deco satellite node.  

Remember that you can mix and match less expensive Deco nodes (X,M,P,S models) to expand your Mesh out to a maximum of TEN satellite nodes. If you want to maintain the full speed of the X20, then add more of them to the mesh. All with the exception of the M3W can use wired Ethernet as a backhaul.

Good Luck and enjoy your Mesh !

@Chucktin 

BTW .

You can use the Web interface from a browser to partially manage the Deco Mesh but the Mobile APP is the preferred method and is full function, unlike the web interface.