Shack On 2nd Floor, Grounding A Gable/Eave Mounted Antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KT4JX, Jan 24, 2021.

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  1. KT4JX

    KT4JX Ham Member QRZ Page

    So I've got a gable end / eve antenna mount attached on a 2-story house with a 5-foot mast. The radio room is on the 2nd floor. Coax will come in through the window via a wood board with holes that slides into the window sill. If I use a lightning arrester, will I literally need to run a long piece of bare copper wire from the 2nd floor all the way down to a lightning rod down on the ground?
     
  2. AK5B

    AK5B Ham Member QRZ Page

    Yep!
     
    N0TZU likes this.
  3. W9XMT

    W9XMT Ham Member QRZ Page

    That run of copper wire from the 2nd floor radio room equipment to a buried ground rod will carry r-f current during the operating times of the transmit system. In effect, it will be a radiating part of the antenna system.

    Such a "ground" lead has the r-f characteristics of Earth potential only where it connects to the top of the buried ground rod. The rest of that lead length can/will radiate e-m energy into space (unfortunately).
     
    WB5YUZ likes this.
  4. G8FXC

    G8FXC XML Subscriber QRZ Page

    I used to have a similar configuration of shack and had great difficulty with RFI. Eventually I tried an MFJ Ground Tuner (https://mfjenterprises.com/products/mfj-931) and most of my problems went away. Operationally, it's a bit of a pain - you need to retune it after any significant change of operating frequency - but it did work and made a significant difference both to the performance of my rig and the interference that I caused to other household items. Like most MFJ products, the build quality is less than perfect, but it worked for me. It's not a complex device and easy enough to build if you have the time to spare - a web search should provide construction details.

    Martin (G8FXC)
     
  5. KA2BLG

    KA2BLG Ham Member QRZ Page

    If you’ve not read, followed and understand @KF5LJW’s pinned posts, you’re probably doin’ it wrong.
     
    AK5B likes this.
  6. KT4JX

    KT4JX Ham Member QRZ Page

    The radios will all be VHF / UHF / 700-800 Mhz, mostly for scanning/receiving, no HF. It will be awkward having a thick copper wire just danging down to the ground. So that long of a ground wire could mess up the SWR?
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    No, it won't.

    UHF antennas, at least all the commercial/industrial properly engineered antennas I've ever seen, are ground independent and couldn't care less if you ground the supporting mast or not. You can't achieve an "RF ground" at those frequencies, anyway, unless that's part of the antenna.

    The reason to ground the mast, and also the outer conductor of the coax where it enters the house, is to reduce or prevent lightning damage only and is required by the electrical code everywhere. There's more to it than that, but really the entire code is driven by fire prevention techniques.

    Even the little DBS satellite-TV dishes should be grounded, no matter where they're installed (if they're outdoors), and in proper installations, you'll see they are.
     
    WB5YUZ likes this.
  8. WA7ARK

    WA7ARK Ham Member QRZ Page

    Maybe awkward, but is required by Electrical Codes. Any coax coming into the house must be "bonded" to the grounding system that is already part of your electric meter.
    It will have un-measurable impact on VHF/UHF SWR. The comments above have to do with bringing coax from an HF antenna into a 2nd floor window...
     
  9. KC3PBI

    KC3PBI XML Subscriber QRZ Page

    Think about this:

    If you use a lightning arrester, wouldn't you want the entire discharge-to-ground path to be outside your home? If the antenna takes a bad hit, chances are a lot of this wire will vaporize and throw hot slag.

    How bout we leave that possibility outside the walls by running the wire neatly down the side of the house?
     
    AK5B likes this.
  10. KT4JX

    KT4JX Ham Member QRZ Page

    Understood, thanks. Yes, this grounding will be for lightning safety, not RF performance. I've been thinking of getting one of these DX Engineering DXE-UE-2P Boxes as a waterproof way of hooking everything up. I will need a new ground rod installed as the house's 2 electrical ground rods are far away on another side of the house.

    But lemme ask this. Should the ground wire be at least a few inches away from the outer wall as it runs down from the 2nd floor?
     

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