Does Cable Box send signals via Power Cord?

[KX9DK]

Noticed I'm getting nice HD reception directly from cable modem. HD cable box not part of the circuit except for power cord being plugged in (nothing attached to input or output connectors). If I unplug cable box power cord my Samsung HDTV loses reception. Strange....unless some kind of communication being sent via power cord....
See attached diagram.
Thanks,
Dave

diagram of setup

[techboywi]

Cable modems due have cable tuners in them, but I believe only certain frequencies. Not sure if there is any filters used, but that could explain some of what you are seeing

[Deep Thought]

Most cable companies send the x.1 main OTA local HDTV signals in the clear and any receiver with an QAM tuner can receive them. Why yours went away when the cable box was unplugged is a mystery. I don't understand how you have the cable modem connected to the TV, though.

[NECRAT]

Is the RF feed looping through your cable modem?

Sounds to me like you're getting ingress through cable leakage.

[w9wi]

Noticed I'm getting nice HD reception directly from cable modem. HD cable box not part of the circuit except for power cord being plugged in (nothing attached to input or output connectors). If I unplug cable box power cord my Samsung HDTV loses reception. Strange....unless some kind of communication being sent via power cord....
See attached diagram.
Thanks,
Dave

hdtv2.jpg

I see you're in Waukesha.. (looked up your call on QRZ)

In Menomonee Falls that connection will work fine. The local OTA stations' signals are carried in HD in the clear -- you don't need a cable box to get them -- though TW doesn't broadcast the fact..

What I can't explain is why it goes away when you unplug the cable box.

[Baylink]

What *I* can't figure out is how your cablemodem is working with no AC power.

:-)