Question: how do i get a ground on rocky soil?

Discussion in 'Antennas, Towers, Feedline, Grounding' started by 4Z1UG, Jun 23, 2016.

  1. 4Z1UG

    4Z1UG Eric, 4Z1UG

    My house is on solid rock, limestone I think, and is made of concrete and steel re-bar. This is the construction technique here in Israel. My ham shack is now on the top floor, three stories above the back yard. I have two ground rods where we had to dig and break rock to get them into the ground. On each of the house at street level are two copper tabs, 4" x 2" x 1/4 " sticking out of the wall labeled electrical ground. The builder must have tied the ground buss from the electric to these two bars sticking out on each side.

    Is this ground the best I can do for a ground in this soil?

    shackgnd.PNG Ground tab 1.PNG
    Ground tab 2.PNG
     
  2. n6gn

    n6gn Glenn, N6GN

    I think you need to examine the reason and use of a "ground". The common reason is to provide an image plane, a surface about which an antenna is reflected for matching and feeding. As such, if you use a balanced antenna, one which already provides this function based on its symmetry, there is no use for a ground. It then serves only as a plane about which a (balanced) image antenna is reflected. On most soils, this results in more of the main lobe of the antenna reflected upward, away from the the horizon.

    So, if you are trying to get a ground in order to effectively couple into the antenna, then perhaps your best bet is to change your antenna type - don't try to use the physical ground to create the reflection plane. In that case, getting the antenna *away* from ground, as high as possible, may be the goal. If instead you are trying to use the 'ground' with an asymmetrical antenna such as a monopole, then about the only thing you can do to improve the quality of a physical ground to mirror the currents in the real antenna is to lay radials and create a ground where there wasn't one. This may require a counterpoise or else actual radials at ground level, depending upon where you choose to mount the antenna.

    Your goal may depend upon the desired radiation angle (and efficiency). On receive, the ground associated with the image of an unbalanced antenna may make little difference since inefficiency only results in a higher noise floor, but one that may not approach the QRN from local sources. This is why relatively inefficient antennas, like loops and short whips, may provide just as high S/N from a receiver as a full size dipole at elevation. On transmit, the efficiency and ground losses tend to matter more since it's ERP that counts and grounds that are imperfect may absorb transmit power.

    Ask yourself what your goal is, what efficiency and radiation angle you need and which gives you the best performance on receive as well. Low angles may result in high suburban QRN!

    Glenn n6gn
     
  3. 4Z1UG

    4Z1UG Eric, 4Z1UG

    Dear Glenn,

    Thanks for your reply. I guess that I am more concerned with station grounding and lightning protection. I thought to build a 40 meter inverted V fed with window line (450 ohm) using my Heathkit Auto-Tune antenna tuner. The top will be at 50 feet above the back yard. I can also do a 20 meter delta loop. Just below the mast is a ground rod, and I though to use two spark plugs as lighting arrestors for my window line where the bottom of the mast is tied to one of the ground rods. The only station ground that I have is from the ground wire in the electric plugs. For now my UHF antenna is in the attic. Once it is moved outside on the roof it will be directly above one of these ground tabs that could be used for lighting protection with a gas tube arrestor at the bottom of the antenna mast. What do you think?