Cable Modem Signal Levels revisited

Fourteen years ago I wrote a blog post about the signal levels that come in and go out of your typical cable modem. Some things have changed some stayed the same. Let’s revisit this topic.

The IP address to connect to a cable modem is still the same 192.168.100.1. These days, I’m still using a LinkSys router but a newer model, the WRT3200 ACM with its IP address and subnet set to 192.168.200.1 : 255.255.255.0

This particular router and my setup doesn’t seem to require the creation of a static route anymore, opening a web browser at this URL: http://192.168.100.1 opens the status page of my Arris SB6183 cable modem.

We don’t live at the same place anymore and one of the first things I did, when we moved into our current location, was removing all unnecessary connections from coax-cable that enters the home (POE = Point of entry). I also put a POE filter on the coax to prevent any unwanted signals from leaving the home (more on that later) and replaced the five-way splitter with a two way, only connecting the office and the living-room.

POE Filter

“The BELDON PPC MoCA “Point of Entry” filter Model SNLP-1GCW serves as in-home networking services pass-through for the 5-1002MHz band while providing an excellent termination for the MoCA band from 860Mhz to 1525MHZ. The device physically isolates the subscriber premise by providing a band stop at the networks Point of entry “POE” This avoids interference from other MoCA users. The device provides a perfect termination for the MoCA band and reduces micro reflections that would typically reduce the data throughput.”

Two-Way Splitter

BAMF splitters use a frequency spectrum of 5-2300 MHz for optimal performance on all devices. Whether you are using a cable (internet, TV, or phone), satellite TV, or antenna system. They work great with MoCA systems and are made to connect to any size of coaxial cable, which includes newer RG6 cable or older RG59 cable.

Cable Modem

We don’t get Gigabit speed internet service around here, in fact the download speed is capped at about 150 Mbps and upload at about 8 Mbps around here. Our internet provider only supports DOCSIS 3.0 modems, meaning that the Arris SURFboard SB6183 cable model is a good fit. Download speed is nice for watching high-quality videos, while upload speed is important if you want to look good yourself, during a video conference.

With my Internet Service Provider (ISP) and service plan, I get 16 downstream channels and 2 upstream channels. Opening the above-mentioned status page of the cable modem shows important information about each of those channels:

  • Power Level
  • SNR (Signal to noise ratio)
  • Corrected and uncorrectable packets

For the downstream channels, the power levels should be in the range of [-10 dBmV .. +10 dBmV] and they should also all be within three dB of each other.

For the upstream channels the range is [+35 dBmV .. +50 dBmV], and again should all be within three dB of each other. For some networks, the power limits for 3 to 4 channels are 35 to 51 dBmV. Ideal levels are approximately 40 to 50 dBmV for single channels, 37 to 48 dBmV each for 2 to 4 channels.

The Signal to Noise Ratios should also all be within three dB of each other. However, for power level -15 to -6 dBmV the SNR should be 33 dB or higher and for  -6 to +15 dBmV the SNR should be 30 dB or higher.

A large number of uncorrected packets (thousands or more) reported over a longer period, might still not signal a problem, at least not if it is less than 20% or more of the corrected packets.

The information provided by my modem after an uptime of a little more than 7 days doesn’t look all that great, but for my ISP it’s probably more than acceptable.

The power levels for the downstream channels are in the range of 2.7 .. -3.1 dBmV.
The power levels for the upstream channels are in the range of 47.5 .. 50.3 dBmV.

SNR range is 33.2 .. 34.7 dB but the uncorrectable are almost 24% of the corrected packets at one of the downstream channels.

MoCA

To provide the Apple TV, which is on the other side of the one-story home, with a fast Internet connection, I use a pair of Motorola MM1000 MoCA devices. MoCA stands for Multimedia over Coax Alliance, allowing to feed Ethernet back into your home coax cable network.

Motorola MM1000 MoCA Bonded 2.0 Adapter

With MoCA devices, the COAX cable in your home can be used to create Ethernet connections and it doesn’t matter if you also already use the COAX for internet and/or TV channels.

Typically the range of frequencies that are delivered to our homes for television signals is 54 MHz to as high as 1000 MHz (though many current systems only support 750 MHz or 860 MHz). While the upstream is what is returned from every house back to the cable operator’s headend. This frequency range is typically from 5 MHz to 42 MHz.

This leaves frequencies above 860 MHz available to distribute Ethernet throughout the home. Now it should also start to make sense why the POE-Filter prevents frequencies above 860 MHz  leaving the home and the splitter having a frequency spectrum of 5-2300 MHz.

Anyways, long story short, one MoCA device at the router, and one at the Apple TV bridges the gap at my house very nicely.

 

Share this post:

Leave a Reply