9

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.

DavidRecallsMonica
  • 1,612
  • 1
  • 6
  • 18
Andrew
  • 93
  • 1
  • 4
  • 1
    Won't hurt to try except some time, but doubt if it would work. Should check out https://www.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 '22 at 19:36
  • You would need a very strong signal. How close are you to the transmitter? – Chenmunka Mar 26 '22 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 '22 at 19:57
  • 4
    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 '22 at 20:20
  • 1
    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 '22 at 20:22
  • Finally, the FCC has an OTA antenna tool that you enter you zip code or detailed location information and it tells you what kind of reception you can expect and what kind of antenna would work. https://www.fcc.gov/media/engineering/dtvmaps – SteveSh Mar 26 '22 at 20:24
  • It depends where you are. If you've got strong signal you can probably just stick a paperclip in the antenna terminal. If you've got poor signal you might need a very good, expensive, engineered antenna. I'd try the paperclip first. And a coat hanger next. – J... Mar 27 '22 at 22:10
  • I'd recommend getting the longest, most "powerful" yagi array antenna you can find. The array is a long stick with arms on it, and a sort of reflector at the back. Point the length with the arms towards the TV transmitter, and it'll receive that without all the noise you'll get from elsewhere. Even in an attic space that should work pretty well, so long as you've got approximate line-of-sight to the transmitter. – Ralph Bolton Mar 28 '22 at 10:40

2 Answers2

22

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.

FreeMan
  • 37,897
  • 15
  • 71
  • 155
  • 13
    _"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 '22 at 00:43
  • 1
    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 '22 at 11:26
  • 10
    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 '22 at 17:39
  • @Freeman - As draconian as you may think those HOA regs are, just remember that people enter into those agreements freely when they purchase their property. – SteveSh Mar 27 '22 at 18:12
  • 4
    @Andrew Straight from the FCC: https://www.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. – user1937198 Mar 28 '22 at 00:20
  • 3
    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 '22 at 12:22
  • +1 and LOL @ "I'm sure they've got a ton of questions about antennas and people who would love nothing more than to expound on it." – R.. GitHub STOP HELPING ICE Mar 28 '22 at 14:14
  • I believe the FCC antennae rule came about during the push to Hi Def television. The FCC was obsoleting 50 years of television technology, and they didn't want to force TV users into needing to purchase cable or satellite TV. Any existing HOA regs were annulled. Any new ones are illegal. Get a simple _Batwing_ antennae. I have one with about a 5 or 6 ft (< 2m) span mounted about 10 or 12 feet (< 4m) off the ground and it works like a charm (for transmission towers about 35 miles/50 km away) – Flydog57 Mar 28 '22 at 20:25
  • 1
    @Andrew If the results of your attic antenna aren't acceptable, try an amplifier near the antenna(!) to push that signal through the length(s) of your required coax. The difference can be like night and day. – kackle123 Mar 28 '22 at 21:19
5

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.)

Kevin Reid
  • 3,583
  • 28
  • 29
  • How do they transmit horizontally-polarized signals from vertical towers? – user253751 Mar 27 '22 at 22:07
  • 3
    @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 '22 at 22:38