Bringing this thread back up with GOOD NEWS
....
We had to have a Comcast service tech come over today to investigate a problem with intermittent one way outgoing dropouts or on-connect complete lack of outgoing packets on our landline VOIP phone service. I had already confirmed that this problem was not due to our in-house copper circuits or phones, which the tech also confirmed. He also replaced the cable grip support wire loop on the house end of the drop from the street, which I discovered had apparently snapped during one of the nor'easters that by this month. This resulted in the cable pulling at a sharp right angle on a small clamp about 5 feet below the cable support hook. I tried to get the tech to replace the drop cable, as it is now over 35 years old, but a signal level check showed all was OK, he showed me the spectral plot of the feed he made coming into the modem. Since the VOIP problem has been intermittent, and was not happening during the service call, he offered to swap out our cable modem for a new one. He installed an Arris Model TG1682G, which of course supports the VOIP landline. So far so good on the VOIP problem. It also brought my data download data rate up to over 150Mb/sec, we were limited by our old modem to a nominal 50 Mb/sec.
As soon as he left, I went down to check on the cable modem RFI that I have been living with for a while now, which was especially bad at the low end of the HF spectrum, including the BCB, 160 and 80 meters. What a HUGE improvement...NO modem RFI at all, I am now noise floor limited (but not much) by a neighbor's oil burner cycling, I haven't been able to hear that in years, and it's very low SNR when it's intermittently present.
The twenty-something tech seemed absolutely clueless about HF radio...when I told him about the RFI problem I was having with the old modem, he told me that the cable systems use spectrum between 2 and 52 Mhz, and that I should not be operating anywhere over that frequency range!