Why simply moving the coax cable away from power panel can have such huge difference in errors?

Question

I wonder whether anyone has experienced this. My coax cable drop from the cable company emerged through my basement wall close to my power circuit breaker panel.

Initially I hooked up the coax cable directly to my cable modem (Motorola MB8600) as straight down as possible (to avoid bends) to the left of the circuit panel (see picture below) but the cable was close to several thick power cables just to the left of the circuit panel.

But in just 10 hours, my modem shows LOTS of corrected & uncorrected errors (average 40% uncorrected) as well as particularly high numbers (25% uncorrected) for the 732MHz OFDM PLC band (the other channels are QAM256) with SNR around 33 dB and power around -8 dBmV. See screenshot below:

So I tried to bend the coax cable and putting the modem as far away from the circuit breaker and got a VERY DIFFERENT result. After 24 hours, my modem shows 0 errors except the 732MHz OFDM PLC band which still has a lot of corrected errors, but only 0.00006% of them uncorrected. See screenshot below:

Here's a picture of the circuit panel and the current location of the modem. The red line was the cable path before the move (modem was hanging in the air).

I noticed that in the new location, the power level and the SNR is a lot better, which may explain the improvement in errors. And in between the two locations, I have disconnected the cable from the modem to perform some other experiments, but I think I screwed on the cable to the modem with equal tightness.

Anyone has this experience and can explain what happened?

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Addendum. Before I moved the modem to the basement, the original location of the cable is marked by the red line, and the cable from the outside terminates in a splitter that is also grounded. See picture below (red line traces where the outside cable used to go):

A short cable from the splitter extends it upstairs, through a coupler (second red box above), terminating in a wall jack in a room directly above the current location of the modem (so it is a short cable). Another cable connects the wall jack to the modem inside that room. With this set up, the errors in most channels were better, but still significant. See screenshot below:

I thought the splitter and/or the multiple cable segments was the culprit, so I bypassed the splitter by moving the modem to the basement and connecting the outside black cable directly into the modem. But several users commented that it's the modem's proximity to the power panel that is the culprit, so what I'm going to do next is to move the modem back upstairs and connect the outside cable directly to the coupler as far away from the power panel as possible.

Answer 1

Electromagnetic Interference (EMI): Power panels or electrical gear emit electromagnetic fields, in particular when there is a excessive modern flow. These electromagnetic fields can set off undesirable currents in close by cables, such as the coaxial cable, main to EMI. EMI can disrupt the alerts journeying thru the coaxial cable, inflicting errors, records loss, or degraded performance.

Radio Frequency Interference (RFI): Electrical devices, along with electricity panels, emit radio frequency indicators unintentionally. When these indicators fall into the frequency vary of the coaxial cable, they can intrude with the facts alerts touring thru it. This interference can lead to noise, distortions, and blunders in the obtained data.

Signal Degradation: The coaxial cable is designed to lift high-frequency alerts with minimal loss. When positioned close to a energy panel, the cable may additionally act as an antenna and select up some of the radiated electromagnetic energy. This extra electricity can degrade the integrity of the transmitted signal, main to mistakes in the records being transmitted.

Shielding Effect: Coaxial cables have a protect layer that helps defend the internal conductor from exterior electromagnetic fields. However, the shield's effectiveness has limits, and when uncovered to robust electromagnetic fields from the strength panel, it may also no longer be adequate to forestall interference.

Distance Matters: Moving the coaxial cable away from the strength panel will increase the bodily distance between the cable and the supply of electromagnetic interference. As distance increases, the electricity of the interfering electromagnetic fields decreases, lowering the possibilities of interference and blunders in the transmitted data.