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Discussion Starter #21
The channel block filters are a small cylinder, with male and female F connectors, so they could be installed at the splitter that the drop cable connects to. It is those that the techs are supposed to remove when they find them.
That was the culprit. I guess the Rogers techs missed or ignored the memo.
 

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I am well aware of the type of splitter used. They were very common at one time to not only block TV for internet only subscribers but also, prior to Rogers internet, to filter out analog TV theme packs that were not subscribed. If a Rogers tech has not opened the box or gone up the pole since the analog shut down then the splitters will remain. There are probably lots of long term internet or former analog subscribers in that situation. I suspect that there are some new techs who never had the opportunity to install such filters and may not even know what they look like. Rogers really needs to be more proactive, even if it's only to test line levels after an installation or upgrade.
 

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In CATV land, levels are expressed in dBmV, Decibels relative to 1 microVolt, as-opposed to the dBm(deciBels relative to 1 milliWatt that all the other industries use.
I mistakenly used dBm due to habit. Given my radio background, I never got used to expressing the dBmV units during my time in CATV.

I'm super curious as to what other changes the tech performed, as this change in upstream levels cannot alone be caused by a "filter" itself. Perhaps the filter had caused high downstream loss, and connections had been arranged such as to bring a high amount of system gain to the device compensating for the downstream loss, then ending up with such low loss upstream? I know as a tech I was always incentivised to oversimplify my explanations to the customer of what I had done, so as to avoid boggling their mind and reduce my time spent yakking.

Low transmit levels are generally pretty rare, as the designers are motivated to provide only the minimum return-path gain to allow successful connections under the industry-standard range of valid trunk-tap configurations, which keeps noise - and therefore outages - to a minimum. The only times I saw really LOW transmit levels, were in odd situations, such as at the very far-end very old outside plant cabling, where the downstream levels were highly attenuated by the old cable rated for only around 400MHz, the return losses were very low since low frequencies only require very modest performance from any coax, and Tap values were allowed to be very low such as only 4 or 6dB, which you won't find in any modern designed and maintained system. Now the min tap value is about 10. An example that comes to mind of such a situation was in a place where most of the existing outside plant was still original direct-burial 400MHz cable(RG-11), with a mix of old and new taps that were only touched when there was any sort of repair and original old parts were obviously not available. I would get calls for either low TX modems providing terrible service, or else I'd be there for terrible CATV digital reception on channels that were transported at high frequencies such as 600+MHz, or both. I had to use an expensive and delicate mix of upstream attenuation devices, and counter-slope amplification on-premesis to get my re-call rates for that town down to an acceptable level. That town also happened to have a lot of exceptional install scenarios where homes were located on enormous property, with a long drop line, as well as exceptionally low development density(acreages for rich people, business elite), where the usual formulas for outside plant design went right out the window. TL;DR I speak from experience.

Modems cannot just "increase output" until their signal gets sufficient SNR, that would hammer the receiver at the CMTS with signals exceeding it's dynamic range. The ranging process what modems must go through, allows the devices to train their transit-time through the system so that their TDMA signals arrive on-time and don't interfere with their neighbors, as well it establishes the initial level needed to reach the specified receive level(power level) . AGC cannot be used at the CMTS because of the fact that TDMA is used, so all levels must arrive reasonably equally power-wise thus the protocol endures this. After ranging is complete, periodic feedback is provided to the modems from the CMTS to make fine adjustments necessary to maintain the channel(s).
 

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Discussion Starter #24
sparkycivic

I followed the tech as soon as he arrived at my residence. He first checked levels at the RG6 compression fitting at my modem. Levels were noted as low. He also noted the exact cable length to the drop in the box at the curbside - 240 feet total (210 feet of buried RG11 to the demarc and 30 feet of RG6 to the compression fitting at the modem). I know this as I was home the day our service was initially installed. No issues were found with the physical connectivity to the drop at the curbside box from the residence.

Next he check levels at the other side of the drop (pre CATV filter). Levels were good here. So he removed the filter and rechecked levels at the modem. Bingo! Problem solved. As a licensed amateur radio operator, I'm very familiar with insertion loss especially at higher frequencies.

The tech was very good and apologetic that our filter removal was missed post analog cable days. I told him, it was not his fault, just an oversight by the service provider.

Here are our levels as of this morning.
 

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Discussion Starter #25
Problems continue

Upstream and downstream levels are okay. But why am I seeing these continual errors in the log?

 
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