Your cable may be receiving ingress from outdated phone lines or FM signal from nearby cell towers. Check out my post here: https://forums.xfinity.com/t5/Your-Home-Network/Signal-ingress-due-to-outdated-neighborhood-phone-props/m-p/3374867/highlight/true#M335162 To narrow the issue, I recommend hooking up to Ethernet, installing pingplotter.com & then debugging by reading pingplotter's blog.
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@jontalk, I guess I should consider rolling my own modem/router but I do have an update that may point to a deeper issue... ... A technician came by yesterday & identified the issue to be FM ingress. Here are my notes: He ran a diagnostic and found an ingress problem in the signal. This is signal leakage and can occur when an external signal is interfering into the cable. This results in noise & disruption of the desired signal, usually seen as packet loss. When he started unscrewing the splitter from the cable, he felt an electric shock. He then took out a Foreign Voltage Detector (FVD) that shot up when he brought it next to the cable. This indicated an AC current was going through the wire which it's not supposed to. This led him to conclude that an electric signal was passing through the cable when it shouldn't. Looking at the outside setup, he identified that the neighborhood is still using old phone cable prop boxes. These boxes send an electric signal through the wire since old phone lines needed that. This electric signal is the cause of signal leakage and causes FM ingress in our cable. This manifests as a packet loss in our internet connection which ultimately leads to slower internet connection than what you're paying for. So it seems like an outside network issue is at fault here. To back up this claim, I checked out the modem's 10.0.0.1 & tried to find a pattern in downstream/upstream signals. Here is the table: https://imgur.com/a/qJFMGPq I used this link as a reference (https://arris.secure.force.com/consumers/articles/General_FAQs/SB6141-Cable-Signal-Level/?l=en_US&fs=RelatedArticle#:~:text=Acceptable%20SNR%20Levels%20(dB)%3A,be%2033%20dB%20or%20greater.). Specifically: Upstream Transmit Power Level Channel US Channel Type Symbol Rate Acceptable US Power Level Single TDMA 1280 Ksym/sec +61 dBmV to 45 dBmV ATDMA 2560 Ksym/sec +58 dBmV to 45 dBmV 5120 Ksym/sec +57 dBmV to 45 dBmV Two TDMA 1280 Ksym/sec +58 dBmV to 45 dBmV ATDMA 2560 Ksym/sec +55 dBmV to 45 dBmV 5120 Ksym/sec +54 dBmV to 45 dBmV Three or more TDMA 1280 Ksym/sec +55 dBmV to 45 dBmV ATDMA 2560 Ksym/sec +52 dBmV to 45 dBmV 5120 Ksym/sec +51 dBmV to 45 dBmV Notice that my upstream power level never exceeds 42.77 dBmV but the acceptable level is 45 dBmV and up. Does any on the forum think this is proof of what the technician was saying? I'm not a network engineer so I don't know the accepted variance on the power level (e.g. is 42.77 "close enough" to 45 or is it out of range). This *feels* right but I want to make sure it's actually right as I continue my conversation with Comcast. Not sure if they read these forums 😕
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