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Signal ingress due to outdated neighborhood phone props

Regular Visitor

Signal ingress due to outdated neighborhood phone props

Internet plan: "Download as fast as 600 Mbps" - $152/month

Location: San Francisco, CA 94127

Voice and Data Modem
Serial #: 14C03E97E191

Context: I am living with 2 other people; they use WiFi and I use direct Ethernet connct.
The setup is 1 Ethernet connection to Google WiFi points & 1 Ethernet connection directly to my laptop. For purposes of this discussion, I'm excluding performance of my roommates. I am only discussing problems I'm seeing.

Connection: Ethernet (CAT5E) with Belkin USB-C (supports 10/100/1000BASE-T)

Representative sample: September 29, 2020 at 11AM - 12:36. Average of 100Mbps (Ethernet), 29Mbps (WiFi). Paying for 600 Mbps

I've been experiencing poor internet consistently for the past few months. To define poor: I'm paying $152/month for "download as fast as 600 Mbps". Since I'm connected to Ethernet, I define poor as anything less than 200 Mbps performed on at any given time.

I think I've eliminated a few options:
* WiFi is NOT the problem: I've been Ethernet connected on CAT5E cable with an adapter that supports 10/100/1000BASE-T. My MacBook Pro is 2019.
* Data caps are NOT the problem: We have 1229GB data cap but have spent at most 749GB in any given month.
* Running on or off VPN does not matter: I've tried both PIA VPN and without a VPN
* DNS choice does not matter: I've tried both and ISP-provided
* Device is NOT the problem: I've tested the Ethernet connection on another laptop. I've also tested WiFi speed on my phone & laptop & they're both performing
poorly (in WiFi case, poor can be defined as < 50 Mbps performed on

I read a few posts on the forums (e.g. At this point,
I believe the problem has to do with rented modem hardware or street cable (correct me if wrong):

* Modem is outdated or incorrect - PingPlotter is reporting some packet loss. I'm familiar with the software so not sure what to read -

* Connecting between modem & outside is faulty - gives me some output but I'm not a network engineer so not sure what to look for -

At this point, I believe I have to contact Comcast Support to send a technician to fix hardware issues. Does the forum have any idea on what might be causing this internet and if contacting the technician is the right next step? Cheers!



Re: Paying $152 for 100 Mbps - hardware or cable issue - should I contact support?

Is the modem stated here yours or the Gateway device supplied by Comcast? I'm paying for the basic Performance Plus tier (100 mpbs) and have my own Arris SB-6141 modem and Asus RT-AC56R router. I consistently get 120 mbps both wired and WiFi. Your situation sounds like there's a bottleneck somewhere in the network or its faulty equipment. 

Regular Visitor

Re: Paying $152 for 100 Mbps - hardware or cable issue - should I contact support?

Hi @jontalk,


It's the Xfinity Xfi gateway product that they provided with the subscription. I do agree that it's probably a network issue. After running PingPlotter for the whole day, I'm recording 2.6% packet loss with a period of 2 hours where it was averaging 4.7% packet loss. The latency on this averages 3s. Reading this answer (, I do wonder if forum users can echo the following solution:


* Problem: The issue was caused by severe damage to the node, box, on the side of my apartment. As my technician explained, "It looked like someone took an ice pick to the seal."

* Solution: He swapped me to a new slot and replaced everything. In addition to this, he replaced the tip of every coaxial cable in my apartment with compression and removed any splitters, checked my frequency levels before and after the switch, swapped my modem to the best manufacturer in his opinion, made reccomendations, and explained everything along the way. 




Re: Paying $152 for 100 Mbps - hardware or cable issue - should I contact support?

That was pretty severe packet loss prior to the equipment swap etc. You didn't state whether anything changed though. Are you getting the 600 mbps you're paying for? You seem technically astute so I'm curious why you wouldn't invest in higher quality, separate devices rather than pay rent for inferior Comcast equipment. The gateways are low cost items for Comcast since they're purchased in huge quantities. If you think about it, buying your own will pay for itself in no time PLUS delivering more control and better speed!

Regular Visitor

Re: Paying $152 for 100 Mbps - hardware or cable issue - should I contact support?

@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 & tried to find a pattern in downstream/upstream signals. Here is the table:


I used this link as a reference ( Specifically:


Upstream Transmit Power Level
ChannelUS Channel TypeSymbol RateAcceptable US Power Level
TDMA1280 Ksym/sec+61 dBmV to 45 dBmV
ATDMA2560 Ksym/sec+58 dBmV to 45 dBmV
5120 Ksym/sec+57 dBmV to 45 dBmV
TDMA1280 Ksym/sec+58 dBmV to 45 dBmV
ATDMA2560 Ksym/sec+55 dBmV to 45 dBmV
5120 Ksym/sec+54 dBmV to 45 dBmV

Three or more
TDMA1280 Ksym/sec+55 dBmV to 45 dBmV
 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 😕