3 weeks ago - last edited 3 weeks ago by RogersCorey
Hello, I just received my new XB8 modem after signing up for a self-install. My home had Rogers some 8 years ago. The existing setup from the previous install had a 3db attenuator on the coax before entering the old Hitron Modem. I would like to know whether to keep or discard the attenuator when plugging in my new XB8 Modem. I am looking for the coax signal strength charts (DOCSISWAN tab) on my new XB8 modem but can;t seem to find the option anywhere. Any suggestions? Thank you.
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3 weeks ago
Located. Thank you.
3 weeks ago
Located. Thank you.
3 weeks ago
@misc9700 note that the Comcast XB6, 7 and 8 modems use the traditional Quadrature Amplitude Modulation type signals and the much newer Orthogonal Frequency Division Modulation (downstream) and Orthogonal Frequency Division Multiple Access (upstream) signal type.
The OFDM and OFDMA channels use thousands of low power sub-carriers for data carriage, compared to the traditional higher level QAM signals.
Traditionally, previous modems using QAM only would run with a zero dBmV target on the downstream side and 36 to 40 dBmV target on the upstream side.
While that is generally still applicable to the XB6, 7 and 8, Rogers has been cranking up the signal levels at the neighbourhood nodes in various places, so, if you happen to have a steady increase in signal levels across the board to some ridiculous level, don't be surprised. That is what I have from my neighbourhood node, a 9 dBmV increase from the lower to upper frequencies. So, not only is there an increase in the signal levels, the signal tilt, which is a steady increase makes in generally impossible to use a signal attenuator to bring the signal levels back down to a reasonable level. That is due to the OFDM channel which usually exists in the 350 to 447 Mhz range and the possibility of an upper OFDM channel in the 900 Mhz range. If you bring down the upper OFDM channel, there's a good chance of dropping the lower OFDM channel down to a signal level that impairs its use. So, that is signal tilt and overall signal level dependant. Just pointing this out due to the low signal level data sub-carriers in the OFDM and OFDMA channel coupled with the possibility of extremely high signal levels, which is an attempt to transmit the data sub-carriers at a level that their actually received by the downstream modems.
Fwiw.....
3 weeks ago
Hi Datalink,
Thank you so much for your insight.
Before reading your response, I went ahead and hooked up the new XB8 modem, using the 3db attenuator that was in place for my previous Hitron modem. Below are the results that I obtained. Do you recommend that I remove the 3db attenuator?
Thank you ever so kindly in advance!
Channel IDLock StatusFrequencySNRPower LevelModulation
Downstream | Channel Bonding Value | ||||||||||||||||||||||||||||||||
9 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 |
Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked | Locked |
621 MHz | 279 MHz | 579 MHz | 585 MHz | 591 MHz | 597 MHz | 603 MHz | 609 MHz | 615 MHz | 633 MHz | 639 MHz | 645 MHz | 651 MHz | 657 MHz | 663 MHz | 669 MHz | 675 MHz | 681 MHz | 687 MHz | 693 MHz | 699 MHz | 705 MHz | 711 MHz | 717 MHz | 723 MHz | 825 MHz | 831 MHz | 837 MHz | 843 MHz | 849 MHz | 855 MHz | 861 MHz | 350000000 | 920000000 |
39.6 dB | 39.3 dB | 39.6 dB | 39.6 dB | 39.8 dB | 39.7 dB | 39.8 dB | 39.8 dB | 39.0 dB | 39.4 dB | 39.5 dB | 39.5 dB | 39.5 dB | 39.3 dB | 39.1 dB | 39.2 dB | 38.7 dB | 39.5 dB | 39.5 dB | 39.5 dB | 39.5 dB | 39.5 dB | 39.5 dB | 39.6 dB | 39.6 dB | 38.8 dB | 38.8 dB | 38.8 dB | 38.7 dB | 38.7 dB | 38.6 dB | 38.4 dB | 38.7 dB | 38.2 dB |
9.0 dBmV | 9.7 dBmV | 9.3 dBmV | 9.2 dBmV | 9.4 dBmV | 9.4 dBmV | 9.2 dBmV | 9.4 dBmV | 9.1 dBmV | 8.9 dBmV | 9.0 dBmV | 8.9 dBmV | 8.9 dBmV | 8.6 dBmV | 8.6 dBmV | 8.6 dBmV | 8.8 dBmV | 8.8 dBmV | 8.8 dBmV | 8.8 dBmV | 8.9 dBmV | 9.0 dBmV | 8.9 dBmV | 9.1 dBmV | 9.2 dBmV | 7.2 dBmV | 7.1 dBmV | 7.0 dBmV | 6.8 dBmV | 6.7 dBmV | 6.4 dBmV | 6.2 dBmV | 9.6 dBmV | 7.4 dBmV |
256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | 256 QAM | OFDM | OFDM |
Channel IDLock StatusFrequencySymbol RatePower LevelModulationChannel Type
Upstream | Channel Bonding Value | |||
1 | 2 | 3 | 4 | 10 |
Locked | Locked | Locked | Locked | Locked |
21 MHz | 25 MHz | 32 MHz | 38 MHz | 42 MHz |
2560 | 5120 | 5120 | 5120 | 0 |
33.0 dBmV | 34.0 dBmV | 34.5 dBmV | 36.0 dBmV | 32.0 dBmV |
QAM | QAM | QAM | QAM | OFDMA |
TDMA_AND_ATDMA | ATDMA | ATDMA | ATDMA | TDMA |