Antenna Grounding Advice

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KJ6EWX, Feb 12, 2018.

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  1. KJ6EWX

    KJ6EWX Ham Member QRZ Page

    Hello All,

    I am a Tech and am installing my first base station antenna on my newly constructed house. The antenna is a Comet GP-3 and will be mounted on the third floor roof. (I will eventually get my General and somehow install an HF antenna). My radio for now is a Yeasu FT-7900.

    First off, I am in Southern California where there is not much ‘weather’ to speak of. Also all of our utilities are underground.

    Its a bit of a restricted situation as the area I live in we have no yards, only 3ft walkways on each side of the house (6ft between houses). I have no exposed dirt, all the property is poured cement. My ground rod is located on the back corner of the house, inside the exterior wall which happens to be the garage wall. The garage is also where I will have my radio.

    I’ve come up with two ‘routes’ for the coax from the antenna, and 1 route for the ground wire. See the attached drawings. My ground rod is on the opposite side as my antenna location, so I will need to route around the house. I know the route for the ground is a bit convoluted, but I hesitate to run it under the house. Coax Rt#1 follows a railing overhang around the house and down the opposite side. It drops down the outside and goes through the wall to the radio. The ground wire route follows the same path, but drops down in a different location (pic 2). It then goes into the wall and ties in to the ground rod. (If this route is even possible safety speaking). Coax Route #2 would drop down the side of the house, enter a foundation vent, then continue to the garage under neath the house to emerge as needed for the radio.

    I appreciate your comments and opinions. Thanks.


  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    You don't need to run a ground wire from the antenna directly to your ground rod. From a safety standpoint you should ground your coax shield at the point where it enters the house and that ground should either be the service entry ground rod or be bonded back to that service entry ground rod with a heavy gauge conductor.

    That's per the NEC requirements and helps to minimize ground differential issues due to any lightning events in the area. Note those aren't necessarily or even typically direct lightning strikes, they're regional events that induce a surge on either your antenna system or more likely the area AC distribution lines (not as likely where you live and with your local lines buried but still possible). The grounding just minimizes any grounding differential voltages during such surges.

    From an RF standpoint the Comet GP-3 already includes its own RF return so there's no RF advantage to running that ground line.

    Anyway, you don't really need the independent grounding line from the ground rod to your antenna but you should make sure you ground the coax shield to the service entry ground rod right where the coax enters the home so closer to what you show in version 1. For some extra insurance you could mount a good lightning surge suppressor at that same point where the coax enters the home with the suppressor grounded to that service entry ground. Something like this:
    KJ6EWX likes this.
  3. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    I won't give you a full answer... BTW we are discussing lightning grounds not RF (which is not necessary for this type antenna)

    1. Antenna ground wires should always go directly to the ground rod directly below; the shortest route. Routing ground wires around the building is not appropriate.
    2. Drill a hole in the walkway concrete for the antenna ground rod
    3. Run a bonding wire from the antenna ground rod to the service ground rod.
    4. You can route coax any way you want.

    I'm not going to address whether a coax surge suppressor and/or ground is necessary.
    KJ6EWX likes this.
  4. KJ6EWX

    KJ6EWX Ham Member QRZ Page

    Thanks both for your guidance. I'm sure this question gets asked ad nauseum and I appreciate your taking the time to reply..
  5. KF5LJW

    KF5LJW Ham Member QRZ Page

    Ok that means you have no need for any RF Ground, just NEC requirements.

    That makes life real easy for you. You must comply with NEC 810. Don't let that scare you take a look here for the overview or Google NEC 810. What it boils down to you must ground the shield of the coax as it enters the structure and use an ADU (Antenna Discharge Unit) So run your coax down the exterior wall to the garage where the utility service ground is at. Buy a Ground Block with the ADU built-in and kill two birds with one rock.
    KJ6EWX likes this.
  6. KJ6EWX

    KJ6EWX Ham Member QRZ Page

    Thanks KF5LJW, I’ll look into all that..
  7. KF5LJW

    KF5LJW Ham Member QRZ Page

    You are welcome.

    Technically speaking the radio and antenna will operate just fine without any ground because ground serves no functional purpose under normal operating conditions. That does not mean you do not need anything Grounded. Ground in your case is strictly life safety and equipment/building protection. The Ground at the entrance bleeds of static charge, to clear line to ground faults, and reduce lightning and utility faults to safe levels.
  8. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Well not really. Consider that no zoning jurisdiction requires buildings to be retrofitted to meet annual NEC changes. Therefore only a tiny percentage of structures even meet this years standards, i.e. those built or have undergone major repairs/additions in the last year. C0nsider that your neighbor might legitimately still have a 1920's two conductor cloth-wire tube-and-knob installation with fuses and no ground.

    On the other hand, consider the hundreds of millions of TV antennas that have been installed over the last 75 years that were never grounded nor had entrance pulse protection. There was never any epidemic of lightning strikes, fires or destruction. Chances of damage are fairly low, especially in California.

    Very good idea to ground and provide pulse protection. "Must"? Nobody is there to require it; the insurance denial threat is highly unlikely.
    Last edited: Feb 13, 2018
  9. KJ6EWX

    KJ6EWX Ham Member QRZ Page

    KF5LJW, can you link me to an example of a Ground Block with an ADU built in please? I’m not sue I’m finding the right thing. Thanks..
  10. KF5LJW

    KF5LJW Ham Member QRZ Page

    No SIR really. There is absolutely no debate or argument you can make. To suggest or to do so is irresponsible. Telling people to willingly ignore safe practices is just plain ignorant and a defenseless act.

    You cannot ignore code requirements if they are too much trouble or you do not think it is important. No one gives a crap about past code requirements. Nob and Tube wiring are grand fathered. However in that same Knob and Tube house if a receptacle or any kind of circuit were added or modified is REQUIRED TO MEET CURRENT CODE. No question about it. If a permit were required, you would not pass inspection period. If you lived in a rural area without a code enforcement agency you would be a fool and/or a hack trying to cut corners. You would be putting your life on the line.

    The code requirements are crystal clear what should be done. Really simple, bond the coax and use an ADU period. No if ands or butts about it. The ground and ADU is required. There is more to it than just lightning alone. The ground stabilizes voltages thus reducing stress to the coax insulation. It also provides fault protection in the event the coax comes into accidental contact with higher voltages like your 120 VAC, or a Feeder line falling onto the coax. A lot of people had to die, equipment destroyed, and fires to get the code requirement. Lastly it bleeds of static charges so you do not get zapped, jump, and hurt yourself as a result.
    Last edited: Feb 13, 2018

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