said by ModemDoc :
54db cutoff for modems transmitting at lower symbol and lower bandwith rate such as QPSK or 16qam. CV is using 64QAM which is twice the channel width which means lower maximum transmit of about 50db.
For shiggles add a splitter before your modem to create a 3.5db loss and see what it does to your modem.
This level of misinformation is bordering on trolling - and I have to ask you to stop posting purported technical facts that just aren't true.
Not only are you blatantly wrong on your numbers, but the surrounding facts as well:
Transmit modulation change does NOT happen on a per-modem basis and is NOT dependent on how much return signal strength is present: doing so would permit "weak" modems to hog the US channel for a much longer periods of time: That is a concept only happening on dialup modems and WIFI, not DOCSIS. We fail individual modems that are impaired (and if FEC fails enough, they'll fail station-maintenance and dereg and reboot!), not make accommodations for them by letting them talk at lower speeds.
Modulation changes are driven by the CMTS for the entire upstream PORT (and all modems) at once - independent on whether some services (like VOIP) enjoy more robust lower QAM level transmission on a per-grant basis (that's a function of Packet Cable: VOIP traffic can be transmitted at another (selectable) mod level to make it more resilient/stable).