The oddball embedded spectrum analyzer

It’s no secret, the Technicolor home cable gateway sucks. However…. if you have one, try in Chrome or Safari…. (Link will just error if there’s nothing there).

Voila— you have your very own 21st century Graph Channel.

There’s a RF spectrum analyzer in there. Now, it’s not a GREAT one, the minimum frequency resolution is a big wide 6 megacycle wide sweep…. but it’s there.

cable-specOverall view, you can see the bands used for upstream and downstream, divided by a blank band around 100.

That band has some spiky bits in it. What are they? Well… I live within walking distance for the transmitters for a couple of 100KW ERP FM’s…

ENHANCE! There’s 93.5 “The Bull” W228BV-FX; 106.7 WDXJ-FM + HD, 105.9 WBGG-FM, and a few others, all leaking into the cable system at fairly harmless looking levels. I suspect Comcast simply leaves this band of spectrum empty on their cable system to make life easier in the face of RF leakage. (??)


I’ll code a GUI interface in Visual Basic…
The view goes in just enough to make the analog carrier and HD sidebands of WXDJ-FM visible and distinct. It looks like the lower one MIGHT be suppressed a bit – this is an interference mitigation feature present in modern HD exciter firmware from Harris/GatesAir, Broadcast Electronics, and Nautel. You can back it down a bit to be all cool and avoid adjacent channel interference.

I dunno — you can’t expect a spectrum analyzer built into cost engineered nasty home internet CPE to be the best thing ever, but it’s still fun to play with.