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Grounding with an Attic Antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WD9DWT, Nov 21, 2021.

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  1. WD9DWT

    WD9DWT Ham Member QRZ Page

    For a power source, I plan to connect my rig to a 12V deep-cycle marine battery. My station will be on the second floor of a condo with antennas in the attic. I don't think I'll need to ground the rig. But if I do tie the chassis to the green wire ground of the closest electrical socket, I'm afraid it will cause undesirable effects with the antenna system since the electrical wiring also goes up into the attic. Any thoughts?
     
  2. AK5B

    AK5B Ham Member QRZ Page

    If your antenna is in the attic and your power is solely via the battery---no need to ground anything in that scenario (probably the one time this can be said of ham station grounding requirements).

    73,

    Jeff
     
    W4HWD, N0TZU, N8ZL and 3 others like this.
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I'm with Jeff, with a completely indoor antenna and a battery operated rig I wouldn't ground anything.
     
    PU2OZT and WD9DWT like this.
  4. W9XMT

    W9XMT Ham Member QRZ Page

    ... as long as your antenna system is a "balanced" configuration that provides a 2nd radiating conductor to make a complete path for equal currents to flow into one of its terminals and out of the other terminal at the same time, which is a fundamental need of all antenna systems.
     
  5. WA7ARK

    WA7ARK Ham Member QRZ Page

    So why do hams think that it is ok to unbalance an intrinsically balanced antenna like a dipole or invertedV by connecting a coax feedline with the coax center-conductor connected to one side of the dipole and having the unchoked coax shield connected to the other side???? Proper engineering dictates aggressively choking Common Mode currents on the outside (shield) of the coax, at least at the dipole feedpoint, and possibly again where the coax connects to the tuner/transmitter.

    Operating without a choke on the coax grossly unbalances the antenna by effectively providing a conductive RF path directly from one side of the dipole to earth; a path which is sometimes extremely tortuous, involving passing through radio/tuner/power supply chassis, through the AC line cord to a duplex outlet, through in-wall house wiring, all the way to the house's electrical panel and the Electric Utility's grounding system. This path also comes into play in reverse if there are AC-powered RFI producers (switching power supplies and wall warts) in the house, because the house wiring to coax connection provides a conduction path for the RFI to reach the antenna, and thereby to be received as interference by the receiver.

    To David's (@WD9DWT's) attic requirements: Even if your rig runs off a big battery, I'll take a bet that the chassis of your rig will still have an RF path to the AC utility ground (even if isolated at DC), therefore you need to pay attention to what I said in the first two paragraphs. If you are planning to do digital modes, the computer is almost certainly RF grounded, and there will likely be audio or USB connections between the computer and rig. If you have a battery charger to "float" the battery, it will likely have an RF path to the AC in-wall wiring (the negative post of the battery is tied directly to the ham rig chassis), and so on...

    The correct solution is to make sure that the ham station is connected to the safety (Green Wire) ground in your house, and then to mitigate the RFI/CM/antenna unbalance problems by aggressively CM choking the coax feedline, possibly in multiple places between the rig and antenna.
     
    Last edited: Nov 21, 2021
    KJ7RDV likes this.
  6. WD9DWT

    WD9DWT Ham Member QRZ Page

    I will have coax running directly to ground planes as well as to current baluns connected to dipoles. I will have no other equipment hard-wired to the radio besides the microphone. Wrapping the coax with ferrites sounds like a good idea. But I know when the time comes to broaden my capability with accessories, I will definitely have to ground everything to a common ground bus.
     
  7. WA7ARK

    WA7ARK Ham Member QRZ Page

    "Ground planes"? as in VHF antennas?
     
    AK5B likes this.
  8. AK5B

    AK5B Ham Member QRZ Page

    Also not necessary; I think you have been perusing some of the myths that pervade our hobby...

    As long as all of your antennas are inside your attic or otherwise indoors---and---your battery is not connected to anything plugged into the ac outlet while operating---you may consider your station "ground-free."

    That's almost as good as free-range chicken with baked potatoes and stir-fried garlic spinach!

    (edited to add the spinach)
     
    Last edited: Nov 21, 2021
    KJ7RDV, W4HWD, WD9DWT and 2 others like this.
  9. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Exactly.

    You don't need to ground a battery operated rig connected to an all indoor antenna any more than you need to ground a hand held radio.
     
    WD9DWT, N0TZU and AK5B like this.
  10. WA7ARK

    WA7ARK Ham Member QRZ Page

    Good luck with that! That is an invitation for RF burns to the lips, or at least tingling lips...
    In a totally "floating" system, it is a finite size/volume. You walk up to it and transmit. If your skin touches anything, the system is now its original size plus the ~6ft length of your arm/body. You think that there will be no RF current flowing through your skin?
     

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