The oddball embedded spectrum analyzer

It’s no secret, the Technicolor home cable gateway sucks. However…. if you have one, try http://10.0.0.10:8080 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. (??)

spec-fm-band

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.

cable-iboc
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.

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