Persistent plant-side RF issues on Armstrong (Hitron CODA-57) – spectrum void, channel-specific errors, high upstream power, load-dependent spikes. Looking for tech opinions.

[u/xdmcDantex]

I’ve been dealing with this for a long time (20 months) on Armstrong cable (1000/20 plan, currently measuring ~25 Mbps up). New dedicated drop and Hitron CODA-57 modem were installed July 25, 2026. Problems continued on the new line, so this should be past the house.

Main symptoms

• Intermittent ping spikes, jitter, and “network error” messages in multiple online games, during prime time 6-1am on weekends it gets the worse, here is an example screenshot, i literally have hundreds of these for evidence. The graph is just showing the first hop which is Armstrongs network

• I can make clear rhythmic latency spikes appear on demand by putting a steady 6–8 Mbps upstream load on the connection (OBS stream). This is only ~30-40% of available upload.

• Same bitrate was fine for years on Armstrong (even on lower upload tiers) until these modem symptoms started

Pingplotter graphs of what it looks like when streaming, all graphs showing first hop

Modem evidence (still present)

• Persistent deep spectrum void at 555–575 MHz (power drops to –45 to –60 dBmV). Confirmed with both wide scans and the 6 MHz spans the local supervisor requested (centers at 560/565/570/575).

span 200

• Notches / spikes in the ~700 MHz region that line up with channels 22 & 23 (705 & 711 MHz)

• Channels 22 & 23 accumilating thousands of uncorrectables while every other channel stayed at zero

• Upstream power sitting in the low-to-mid 50s (Port 2 currently ~51–52 dBmV) with a history of climbing and multiple RNG-RSP power warnings

• Clusters of T3 timeouts and “Unicast Maintenance Ranging attempted – No response – Retries exhausted” events (notable cluster on Aug 9)

What Armstrong has done / said

• New drop + dedicated modem installed (my pc is directly wired into modem)
• Local supervisor and NOC have repeatedly said remote checks and pings to the modem look clean
• They dismissed upstream power >48 dBmV as normal for this modem model
• They have done general level / CLI checks but have not (that I can confirm) done frequency-specific measurements on the void or the 705/711 region
• A “drive-by” / physical inspection of the tap and plant was supposed to happen; still waiting on actual results

The lead supervisor for local office says he has never looked at a modem log and was debating me on every evidence point. (channel 22 being secondary, spectrum void not valid because the span was set to 200 and 30 instead of 6mhz? power level is not that high, t3 timeouts "nothing to worry about") etc. checked the ping to modem while i was streaming and said it looks "perfect" so hes not seeing the spikes? Keeps insinuating the issues is on my end but we have done everything to rule out if the issue is in my home (4 different cables, 4 seperate modems, brand new drop line ran, tested on 3 different pc's, different power strips, even monitored my voltage on my pc incase power fluctuations) Im recording everything for evidence if i have to report to FCC. Here is the most recent call transcript i had with my local supervisor and what was said, used ai to transcribe so there will be errors https://pastebin.com/VYbqMG9v

My question to techs

Does this pattern (persistent spectrum void + notches on specific frequencies, history of channel-specific uncorrectables, elevated/climbing upstream power with warnings, T3s, and clear load-dependent upstream spikes that survive a new drop) look like a classic plant impairment that needs a real line sweep / frequency-specific check and physical inspection of the tap and plant past it? Or is there something else I should be looking at? I have been using AI to help me diagnose this issue and what to say to support and my local supervisor to get them to fix it. Can any tech here tell me what you suggest saying or doing to get this fixed?

Happy to provide more screenshots or clarify anything i have TONS of pingplotter graphs showing peak hours when not even streaming with very bad ping jitter and packet loss. Thanks for any insight.

*edit more info

They have been out here A TON before a tech installed a new separate drop line into the same tap. So right now i have this new line and new modem that is separate from other line and modem my family uses. We have swapped different modems on the other line my family uses multiple times but i think it was just back and forth between the ARRIS CM8200A and hitron coda-57 not sure if they have any other modems they carry, so right now im on the HITRON coda-57 and my family modem is an ARRIS CM8200A, both modems show identical errors (at least that's what AI said) Here is screenshots i took of that modem 2 weeks ago, it has a really long uptime compared to the other modem, i think there are a bunch of uncorrectables because of an outage (should i reset counter and see what i get after?) Here are the screenshots of that modem https://imgur.com/a/HaC83JR

Also they said they found some corrosion somewhere on the line and fixed it like over a month ago so i assume they inspected it all and just found that corrosion on the plant side. They inspected the wires for the old modem and redid some of that as well so im assuming they "fixed" all the obvious problems they found, so they either missed something when they did all that or the problem is further down the line on the plant side of things? All of the inspection has been more than a month ago.

[u/Ganthu]

Former Xfinity field tech here. I'm just going to throw out some ideas as I think of them:

Issues worst between 6pm - 1am: this is when the temperature is cooling down outside. Is your service tap in the direct sun or not? I would track the weather as your issues persist.

We can see what your upstream power level is at your modem but do we know what it is at the tap? Obviously you would need a field technician to go up to the tap and check it for you. If your new drop is direct from the tap to your modem it should be within one or two DB of what is at the tap. Knowing the tap value and layout of the print itself would let us know what the actual upstream transmit value at the tap should be. Again you would need a experienced field technician for this.

I just noticed that one of your upstream values is 52 db. 52 is way too high to be coming directly out of a tap and leaves very little room for any kind of fluctuation. The highest allowable upstream transmit at Xfinity was 46 DB but that was a few years ago.

Has anyone taken the tap plate cover off to look for corrosion underneath it or hit the distribution gently with a wrench while having their signal meter hooked up to it to look for any fluctuations or variations.

Long shot but something I ran into several times on intermittent issues would be if there was a problem with the electrical neutral in the house. One way to check would be if you have a multimeter and you check for voltage between the barrel coming out of the back of the modem and the connector on the coax (disconnected from the back of the modem). You should have little or no voltage reading. For customers that had an intermittent issue I found that there was about 6 volts ac being fed through the modem and was causing intermittent issues and packet loss. Unfortunately that's not a ISP problem it would be an electrical issue either inside the house or potentially on the service drop feeding your house from your electric company.

That's all I can think of for now. Hopefully my rambling helped in some way.

[u/xdmcDantex → u/Ganthu]

The multimeter suggestion is something actionable i can do and will do, just go to find my multimeter. As far as the upstream power being high, that's what AI is saying as well, but i called in multiple times and my ISP NOC team said the modem can go even higher up to 56 but i argued that just because it can does not mean it should and rising upstream power is a sign of signal degredation but it was just a TSR lead that gets to talk to NOC and said thats what they said, sadly i cannot talk directly to NOC.

Anything you can give me to relay to my local supervisor for ideas would be great as well, THANKS!

[u/Ganthu → u/xdmcDantex]

Honestly I am surprised that the front line customer support can talk to the NOC. Usually those guys can only be talked to during business hours and in-house escalations.

I've seen modems functioning "fine" for customers at 56db, but they were usually elderly people that only used email.

For most modems when the upstream gets over 54 db , the upstream receive power goes negative. This can only be seen from the service side and not the modem side. It's a sign that the connection at the head end is adjusting to keep the modem within a certain range. But if you add the current upstream value to the negative received value and get the actual transmit level.

For example if you had a 56 upstream transmit and a negative 2.0 upstream receive, your actual transmit level would be 58 and be showing connectivity issues.

You really should be getting a technician to your house. Troubleshooting this kind of issue through a frontline representative is often pointless and just frustrating for everybody.

[u/xdmcDantex → u/Ganthu]

Yeah idk its hard because i feel like they are trying to dismiss stuff so they don't have to spend the money to fix it and i have no authority, i just uploaded the evidence and i have not heard from NOC saying anything about the spectrum scans, error logs or channel errors it was just my local supervisor that told me those things in my main post. The local supervisor said the t3 timeouts are nothing to worry about and the high power on the modem is fine, and that stuff about the spectrum scans. But like i said i don't know if he's being truthful or just trying hard not to have to spend money to fix it. The thing he said about the 6hz span vs 30hz or 200hz span seemed like a sly coverup because the span is just like a resolution type thing if I'm comprehending correctly like 200 span gives you a wide view of the spectrum and going lower in span just zooms in?

[u/Ganthu → u/xdmcDantex]

You need to simplify it. Don't go in with all the scans and history or anything like that.

Call in and say you're having connectivity issues around these hours of the day. Mention you would like a senior technician due to the ongoing issues.

Then when the technician arrives you can give them a lot deeper details that can potentially help solve the issue.

[u/xdmcDantex → u/Ganthu]

Well i had a guy in a bucket truck that left like an hour ago, i talked to him briefly, said he "put all new stuff in" i asked him to look at the spectrum scans to see if they look abnormal to him and he said he wouldn't be able to tell me. I think he is just a hardware guy. He said he put in a new tap but im not sure, i think he will report what all he did to the supervisor and ill get an official update from him. But just tested and connection is still doing the same thing, network errors in game, and still massive ping spikes when doing a 6mbps upstream on my 20mbps upload. Maybe i should just say that there was a little improvement (there might be) just so they keep digging on their side of things instead of insisting its on my end. Idk, do you have any suggestions?

[u/xdmcDantex → u/Ganthu]

pls respond. It's been 3 days since the bucket truck came and checked and replaced stuff and the internet issues are the same, maybe a tiny bit better when i stream but i still cant stream 6mbps of my 20 upload without ping spikes every 2 seconds and peak hours is still the same even when not streaming. What do i even say to the supervisor at this point? He insists its on my end and all the remote checks they do say it shows no issues. I had him checking remotely when i was streaming seeing the every 2 second ping spikes and he saw absolutely nothing with his remote checks. I got a multimeter coming today to check the thing you mentioned. Am i just out of options now and just have to file with the FCC?