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I recently replaced a house trap, and as a result, I have a leftover vent pipe that runs from my basement up through my roof. Would it be possible for me to somehow connect a coax cable to the pipe so that it acts as an over-the-air TV antenna? If relevant, I believe the pipe is cast iron but not 100% sure on that.

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    Won't hurt to try except some time, but doubt if it would work. Should check out tvfool.com/index.php?option=com_content&task=view&id=66 and see if your location is good to pick up stations and what antenna you would need. An expensive antenna if needed is only about two or three months of cable, cheap ones probably only the tax.
    – crip659
    Mar 26 at 19:36
  • You would need a very strong signal. How close are you to the transmitter?
    – Chenmunka
    Mar 26 at 19:39
  • I'm within 10 miles of every tower for a channel I want to get, but so far, indoor antennas (placed near ceiling of the room the TV is in) haven't gotten as good of a signal as I'd like.
    – Andrew
    Mar 26 at 19:57
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    Probably not. The vent pipe is grounded through your plumbing system - basically shorted to ground. That would worse than the indoor antennas you've tried.
    – SteveSh
    Mar 26 at 20:20
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    I would try a better indoor antenna, or try moving the one you have outdoors (just as an experiment) or in front of a window.
    – SteveSh
    Mar 26 at 20:22

2 Answers 2

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There is a LOT that goes into making an antenna work properly. That's why the old-school TV antenna has so many little rods sticking out the sides - they have to be certain fractions of the wavelength you're trying to receive or they just won't work properly. Trying to use any old piece of pipe at whatever random length it happens to be will only lead to more tears and frustration. If you want to find out more, go ask over at Amateur Radio, I'm sure they've got a ton of questions about antennas and people who would love nothing more than to expound on it.

Mount a proper outdoor TV antenna to the conduit, run the coax cable into the house through the pipe. Seal the top of the vent to keep rain & critters out.

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    "Mount a proper outdoor TV antenna to the conduit, run the coax cable into the house through the pipe. Seal the top of the vent to keep rain & critters out." -- That's the ticket! The vent pipe is your antenna mount, not the antenna.
    – gnicko
    Mar 27 at 0:43
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    Thank you! Unfortunately, my HOA forbids roof-mounted TV antennas. Looks like I'll be mounting an antenna in the attic after all...
    – Andrew
    Mar 27 at 11:26
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    It should be noted that under U.S. law your HOA can't forbid roof mounted antennas. That advice is worth what you paid for it but I think a little research will show it to be true.
    – Guest
    Mar 27 at 17:39
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    @Andrew Straight from the FCC: fcc.gov/media/over-air-reception-devices-rule The rule prohibits restrictions that impair the installation, maintenance or use of antennas used to receive video programming and certain antennas used to receive or transmit fixed wireless signals. Mar 28 at 0:20
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    For some values of "freely", @SteveSh. AIUI, in many places you have to sign the HOA agreement if you buy the property. Of course, the freedom is to not buy the property. This, however, is a different discussion...
    – FreeMan
    Mar 28 at 12:22
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If you want to try this and see what happens, all you need to do is take the end of your coax and touch the center part of the connector to the pipe, while making sure the outer sleeve of the connector doesn't also touch the pipe. Moving the contact point up and down the pipe will change how it behaves.

That said, there are two reasons to expect this not to work very well:

  • A vent pipe is quite long, compared to the wavelength of the signals you're trying to receive. Longer is not better for antennas — when an antenna is several times the wavelength of the signal, it will have a fairly unpredictable “gain” or “antenna pattern”, being very inconsistent about what it receives well.

    (But for closely related reasons, the idea mentioned above that “the vent pipe is grounded through your plumbing system - basically shorted to ground” is not true — a ground connection multiple wavelengths away will have some effect, again practically unpredictable, but not necessarily a “you receive no signal” effect.)

  • The pipe is vertical, which makes a vertically polarized antenna. Polarization is essentially a sort of angle the signal exists at, and TV signals are by convention transmitted with horizontal polarization. That's why all the outdoor TV antennas you see have “antenna elements” (rods or bowties) sticking out horizontally. (If you've ever noticed that sunglasses can make your computer or phone screen unreadable — that's the same thing, polarization of photons, and the same sort of problem.)

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  • How do they transmit horizontally-polarized signals from vertical towers?
    – user253751
    Mar 27 at 22:07
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    @user253751 - The tower is just used to get the antenna element as high above the ground as needed or is reasonable. The antenna element, itself, will be horizontally polarized.
    – Hitek
    Mar 27 at 22:38

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