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BlueWolf's Howl

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November 27, 2005

Cable Modems and Noise

While reading Broadband Access Technologies by Albert Azzam and Niel Ransom, I ran across this information about Cable Modems and Noise (stuff that interferes with the signal)...

Noise Roots.

In general, network noise problems come from three areas:
1. Within the subscriber's home (70 percent)
2. Drop plant (25 percent)
3. Rigid coaxial plant (5 percent)

Noise Characteristics in the Upstream Direction.

Ingress Noise. Ingress noise is the unwanted narrowband noise component that is the result of external, narrowband RF signals entering or leaking into the cable distribution system. The weak points of entry are usually drops and faulty connectors, loose connections, broken shielding, poor equipment grounding, and poorly shielded RF oscillators in the subscribers household.
Ingress noise contribution includes most if not all FCC conforming RF power levels such as hair dryers, power line interference, electric neon signs interference, electric motors, vehicle ignitions, garbage disposals, washers, nearby passing airplanes, high voltage lines, power systems, atmospheric noise, bad electrical contacts and any open air RF transmissions such as CB and Amateur radio transmissions, leaky TV sets and computers, civil defense, aircraft guidance broadcasts, international short-wave and AM broadcasters.

With all the things that could interfere with the signal, it's often a wonder that it works at all. I know I can tell when my neighbor is using the vacuum - just by watching the intereference on my tv. And I may as well stay in the kitchen until the popcorn is done while using the microwave - since the picture isn't going to be all that great until it's done anyway... So -- next time your picture gets goofy on your tv, remember -- it's the signal; NOT the TV. Going up to the tv and banging on it won't help. It will only break your tv and then it really won't work once the signal clears up.

Oh...and another interesting tidbit >>

Noise Characteristics in the Downstream Direction

Channel Surfing. Channel surfing causes microreflections to appear and disappear. Because the significant sources of channel surfing are close to the receiver, a large but slowly changing ripple in the frequency domain will appear and disappear.

They forgot to mention how damn annoying it is to boot. So channel surfers...repeat after me... I will use the channel guide.

Posted by BlueWolf on November 27, 2005 02:03 PM