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I'm trying to create some automation of switching off the CATV signal on a splitter port.

Using a regular 5V Arduino relay module I've tried to interrupt the wire from the center of the coaxial cable but it didn't work. I guess that it was due to the exposed center wires which acted like small antennas and passed through the signal through the air.

Another idea is to use some active CATV splitter and just turn off the power for the corresponding amplifier but I'm not sure that it will work either.

What would be the proper way of switching off the CATV signal on a splitter port?

Thanks!

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    \$\begingroup\$ Shopping and product recommendation questions are off-topic so you should remove that from your question to avoid closure. If there's a powered splitter then switching off its power would work. Alternatively try shorting the coax centre wire to the shield rather than break (open-circuit) it. \$\endgroup\$
    – Transistor
    Commented Jan 18, 2022 at 23:12
  • \$\begingroup\$ You have an X-Y problem. You want to switch RF signal on a splitter port, in reality you just need to prevent a kid from watcing the RF signal. Get a set-top box which implements parental controls, if current one doesn't. \$\endgroup\$
    – Justme
    Commented Jan 20, 2022 at 16:57

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The problem is that an open relay still has the contacts close to each other, forming a small capacitor. At the somewhat-high frequencies used in CATV, that capacitor has a low impedance, and still lets a weak signal through. The downstream equipment (e.g. TV) has an amplifier in the reception chain that easily amplifies that weakened signal and recovers the information in it.

To avoid capacitive coupling into the downstream line, use an SPDT relay and add a parallel impedance instead of leaving it completely open. I used 75 ohms which happens to also terminate the line.

On the upstream side, termination would also be desirable in the ideal case but probably doesn't matter since most households have unterminated open circuits on their house coax wiring.

schematic

simulate this circuit – Schematic created using CircuitLab

If you still get coupling causing a signal to go through, consider replacing the 75-ohm resistor with a much smaller one or even a short circuit. Note that shorting the line might cause problems if downstream equipment such as a cable modem could ever try to transmit a signal upstream.

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  • \$\begingroup\$ Great idea! However, I've read that it's not a good practice to let open a splitter port. Due to the impedance mismatch there will be signal reflections back to the upstream. Following your idea but using a DPDT (double) relay and an additional 75-ohm resistor it's very simple to terminate both upstream and downstream lines at the same time. PS. Is it possible to add images into comments? \$\endgroup\$
    – Mne
    Commented Jan 20, 2022 at 21:30
  • \$\begingroup\$ @Mne Not possible to add images to comments, but you can edit your question. DPDT also works here - however for home use unterminated ports aren't that much of a concern in my experience, so I figured to leave it open for a simpler solution. An RF-rated DPDT relay will be even better as far as signal integrity. \$\endgroup\$
    – nanofarad
    Commented Jan 20, 2022 at 21:32

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