(8/n)
SUMMARY OF XFINITY'S DOWNSTREAM CHANNEL LAYOUT IN MY AREA
Low band edge: 108MHz. This makes sense - the whole reason I bought this modem over my previous modem, is that the Hitron CODA is the cheapest of the few that Xfinity will provision for more upstream channels (faster upload speeds), which pushes the start of the downstream channels higher
High band edge: 1002MHz
Total span: 894MHz
Total QAM allotment: 540MHz (60.4%) in 90 channels (6MHz each)
Total OFDM allotment: 336MHz (37.6%) in 3 channels (48MHz, 96MHz, 192MHz)
Total unused: 18MHz (2.0%) in 3x 6MHz gaps

108MHz-246MHz: 23x 6MHz QAM channels
246MHz-252MHz: 1x 6MHz unused
252MHz-354MHz: 17x 6MHz QAM channels
354MHz-360MHz: 1x 6MHz unused
360MHz-648MHz: 48x 6MHz QAM channels

648MHz-744MHz: 1x 96MHz OFDM channel

744MHz-756MHz: 2x 6MHz QAM channels
756MHz-762MHz: 1x 6MHz unused

762MHz-810MHz: 1x 48MHz OFDM channel
810MHz-1002MHz: 1x 192MHz OFDM channel

#electronics #docsis #cablemodem

(6/n)
And we get a nice little UI as a result!:
1. A spectrum analyzer with configurable center frequency/bandwidth span
2. Per-downstream-channel plots of Power (in dBmV - remember characteristic impedance is 75Ω here) and Modulation Error Ratio (in dB) over time
3. Constellation diagrams of any of the active downstream QAM channels!

These are pretty cool - someone has done some good work in developing this feature. Lots of companies simply got rid of the spectrum analyzer functionality in their modems instead of fixing the bug after the Cable Haunt (https://github.com/Lyrebirds/Cable-Haunt-Report/releases/latest/download/report.pdf) vulnerability came out a few years ago, which is a shame since it's such a great learning and debugging tool. So I'm happy to see Hitron is actually working on adding this functionality to a modem that didn't have it yet.
#electronics #docsis #cablemodem

(5/n)
The "Spectrum" hidden tab is a little more complicated - the javascript isn't just grabbing some data from a .asp page and displaying it in a table, it's a whole application with buttons and fancy graphs. So I figured out a devtools javascript console incantation to get the main page to load it, ignoring the fact that it's marked as not visible:
```js
$('#maincontent').html('');
var loadPage = "advanced_spectrum.html"
$('#maincontent').load(loadPage, function(response,status){
if (status=="success") {
$("a").unbind("click");
}
});
$('#maincontent').fadeIn();
```

(This is basically ripped from /js/mainApp.js, lines 305-321)
#electronics #docsis #cablemodem

@isagalaev

I had to replace mine last year & settled on an Arris SBG8300.

Aside from a little tinkering with IPv6, it's just been a set-and-forget appliance for me. Our home network is very small(~8 devices); but, there's plenty of room to grow it with this box should the need arise.

I was mainly concerned with it being Xfinity/Comcast compatible for our apt building. Ended up just heading down to our local Best Buy to pick it up.

Good luck!

https://www.surfboard.com/products/wi-fi-cable-modems/SBG8300/

#HomeLab #CableModem