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TV Antenna

Discussion in 'Communications' started by Brian K, Jan 13, 2020.

  1. Brian K

    Brian K Resident Douchenozzle Charter Member Supporting Member

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    I understand that there's no such thing as a "HDTV" antenna and the name is all marketing hype. At it's heart it's still just a dual band UHF/VHF antenna.

    So my question is, can I build a simple dual band j-pole, connect it via RG6 to the ANT/Cable input on the TV and actually pick up OTA broadcasts? Would it need any modification? I've seen some folks mention needing a 300Ohm IMT on their homebrew antennas.
     
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  2. Burt Gummer

    Burt Gummer Nuts Over Lil D. Staff Member Benefactor Charter Life Member Supporting Member

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  3. hp468

    hp468 Member Supporting Member

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    The TV antennas I've always seen are horizontally polarized yagis or log periodics. Quite a bit of difference in gain between those and a normal j-pole, not to mention the change in polarization which may or may not be a huge deal in this situation.

    Feed point impedance on a jpole is around 50 ohms so you wont need a 300-75 ohm transformer. You would only need that transformer if your feed point impedance on the antenna was ~300 ohms. Your swr will be slightly off as is(1.5:1 or so) but not enough to mess with a stub transformer to bring it back to 75ohm for perfect 1:1 IMO.

    I'd imagine it would work, with marginal results at best (obviously depending on your distance from the transmitter). Either way I'm in for results, I say build it and see.
     
  4. Mirac

    Mirac Epic Replies ---> Charter Member Supporting Member

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    Yes !

    I've. Built 2 of these with scrap. Work perfectly.
    One I strapped to my Direct TV dish, makes it directional.

     
  5. hp468

    hp468 Member Supporting Member

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    Out of curiosity have you experimented with the polorization of yours? I'm curious to hear if vertical vs horizontal has much of an effect.
     
  6. Infamous1

    Infamous1 Purty good lookin in the dark Supporting Member

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    Slowly backs out of this thread feeling really dumb...
     
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  7. Brian K

    Brian K Resident Douchenozzle Charter Member Supporting Member

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    There are two stations I want, in opposite directions, so I'm looking for something omnidirectional.

    I know next to squat about antennas and polarization, but I can follow directions well and have plenty of coax, crimpers, and fittings.

    That's why I ask you guys.
     
  8. Car0linab0y

    Car0linab0y Member

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    How far are the stations? If one is close, point the directional antenna at the other one, you can probably still pick up the close one. I had one transmitter site 8 miles away, with the others 40 and 60 miles away near in azimuth.
     
    Last edited: Jan 13, 2020
  9. Gator

    Gator Parts guy Charter Member

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  10. hp468

    hp468 Member Supporting Member

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    The antenna that Mirac posted (DB4 clone) held vertically (as in the video) with no reflector should receive equally front to back (perpendicular to both broad sides of the antenna).

    Polarization simply refers to how the antenna elements are orientated.

    Vertical = | like the antenna on your car/truck, pointed up and down.

    Horizontal = _____ elements laid flat like on the old channel master tv antennas

    I am curious about your Jpole idea though, if you were closer i'd give you a hand with it.

    One thing that does come to mind as a potential issue, when you scan channels (omni directional antenna) you will more than likely wind up with channels bleeding over each other from each of the stations. With a directional antenna, you mostly only pic up the signals from the tower its pointing to (you will occasionally pick up channels on the back of the antenna depending on distance/power of the station).
     
    Last edited: Jan 13, 2020
  11. hp468

    hp468 Member Supporting Member

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    That guys table saw :eek:
     
  12. Brian K

    Brian K Resident Douchenozzle Charter Member Supporting Member

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    SmartSelect_20200113-211143_Samsung Internet.jpg

    I'll give the j-pole a whirl this weekend and see what she does. I can mount it on the old dish mast, and bonus, there's already a cable run from there to the TV. I think I have a 259 to "f" adapter.
     
  13. Button Pusher

    Button Pusher Well-Known Member Benefactor Supporting Member

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    You can use two and a combiner. I have two in the garage attic with a combiner amplifier.
    My wife likes the local stations without using the ATT TV with the Firestick.
    Good to have when the fiber goes dark from power outage and we are on the generator.
     
  14. Brian K

    Brian K Resident Douchenozzle Charter Member Supporting Member

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    Is it really that easy?

    Screenshot_20200113-212454_Samsung Internet.jpg
     
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  15. Oneofsix

    Oneofsix Non-compliance manager Charter Member Supporting Member

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    Yes it is-
    You'd be surprised how difficult it is the explain what that label shows to "experienced" techs...

    Sent from my LG-H820 using Tapatalk
     
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  16. Jake

    Jake Happy to be here

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    Since TV stations are generally horizontally polarized, you will lose a huge amount. Be prepared to tilt the J-pole horizontal, broadside to the station.

    Also, bear in mind that the j-pole is not a broadband antenna. It is designed to work at one frequency. You will need to pick which station to size it for. Pick the one you care about this most, and maybe it will work well enough for the other. The antenna Mirac shows is broadband.

    That design is bidirectional in the horizontal plane, but not very strongly directional at that.

    Here is a better article on the same design: https://www.ifixit.com/News/how-to-make-a-hardcore-hdtv-antenna-from-scraps.

    The balun mentioned in that article will help.
     
  17. Button Pusher

    Button Pusher Well-Known Member Benefactor Supporting Member

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    Last edited: Jan 13, 2020
  18. Mirac

    Mirac Epic Replies ---> Charter Member Supporting Member

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    I have.
    In the garage I have it mounted horizontal to the ceiling, and get the best out of it pointed in the towers direction
    NE out of Asheboro .
    I've tried it on a stick vertical for the house and it's so so.
    Vertical on the old dish, same as the garage antenna.

    Not measured scientific conclusions mind you..
     
  19. noway2

    noway2 Senior Member Charter Life Member

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    Keep the two runs of coax to the antennas exactly the same to help avoid creating interference patterns. Both antennas can pick up common signals and if the runs are different the two signals will hit the receiver out of phase. The combined may or may not work.

    here is a j pole calculator with frequencies set to WFMY one of the ones your after (RF channel 35): https://m0ukd.com/calculators/slim-jim-and-j-pole-calculator/

    I don’t know the bandwidth but you need about six MHz. If the antenna has too little resistance it will be high Q and narrow. A j pole is also tuned for transmitting which you’re not doing. A tuned (length) dipole wire will work too... see the other image in post 4. At those frequencies, your wires will be in the cm length range.
     
  20. Pack72

    Pack72 Member

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    Last edited: Jan 14, 2020
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  21. Mirac

    Mirac Epic Replies ---> Charter Member Supporting Member

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    Here’s one of mine for the house.

    AD9415F5-3D48-4E64-9D78-E4E30259FA1D.jpeg
     
  22. Gator

    Gator Parts guy Charter Member

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  23. Brian K

    Brian K Resident Douchenozzle Charter Member Supporting Member

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    I ended up building a DB4, it picked up 26 or so stations, but Fox wasn't one of them; Fox and CBS share the same "channel" - Fox tower is in Sophia, CBS is on Sauratown Mtn.

    So I bought a cheap yagi...

    upload_2020-1-26_17-40-29.png

    Pointed it right at the tower in Sophia, still get CBS 90 degrees to the left @ 43 miles but no Fox @ 44 miles. Figures.
     
    Last edited: Jan 26, 2020
  24. Pink_Vapor

    Pink_Vapor Well-Known Member Supporting Member

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    At least you didn’t use a meme!
    A89A3B5E-EF14-46A6-84D8-A1FBE883D4A6.jpeg
    @HMP :p
     
    Last edited: Jan 26, 2020
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  25. amnesia

    amnesia Habitual Trader Staff Member Benefactor Charter Life Member

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    No way in heck I’d want that thing on my house. Free or not ;)
     
  26. Pink_Vapor

    Pink_Vapor Well-Known Member Supporting Member

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    I’ve already got a Mohu Leaf indoor antenna. Would one of these options make much of a difference?