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"RF Ground"

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"RF Ground"

A recent thread on the ALPB forum outlines a plan for adding several 8-ft ground rods buried in holes in the earth and surrounded by a moistened chemical compound, to improve the r-f ground used with a Part 15 AM antenna.   Some thoughts about this ...

  • The function of a buried r-f ground used by a monopole radiator is to provide a path for r-f currents flowing in the earth within 1/2 wavelength of the antenna base as a result of its radiation to return to the r-f ground terminal or chassis of the transmitter.  Otherwise the monopole will radiate essentially nothing.
  • Although the added ground rods described above may have a low resistance path to the potential of the earth immediately around them, the r-f currents flowing in the earth beyond that short radius still must travel through the lossy earth for distances of 1/2 wavelength or more, just to reach those ground rods (wherever they are buried).  Therefore the losses in those paths to return r-f earth currents to the transmit system might be higher than expected.

If the site layout and operator risk-taking permit, better operational results might be possible from an effective "r-f ground" or counterpoise using just two 1/4-wave, horizontal radial wires elevated a meter or so above the surface of the earth, running in opposite  directions from the base of the monopole, and joined to each other and the transmitter chassis there.

When properly installed, such elevated wires contribute no useful far-field radiation of their own to the transmit system.  But note that this antenna system configuration is not explicity permitted by FCC §15.219(b), so it is not without risk of FCC attention.

Link Coming Up

The ALPB will provide a Link from the referenced "Grounding Again" item directly to this post for the convenience of users.

Carl Blare

RF Ground

Rich,

Thanks for the advice.  However I have no intention of adding any "elevated" ground radials for the very reason that they might take me out of compliance.  Currently I have about 30 ground radials ranging in length from 30 feet to 30 meters as my property permits. Based on the maps I have seen the ground conductivity here is pretty poor and from observation I can tell you it is very rocky.  We had to bring in boat loads of top soil when we built the house.  When I originally installed the ground radials it seemed to greatly increase my coverage area to about a mile in most directions but in some directions I assume anyone without a DXer's attitude might not wish to listen, but for sure the coverage is very solid for at least a half mile in any direction, during the DAYTIME. Luckily my home is a good 150 feet above street level, and as my property continues to slope upward behnd the home the transmitter is at about the height of my home's roof. I know that MW is not line of sight but the elevation is certainly not a negative, IMO!  I figure this project cannot hurt, and only help.  Except for the Terra-Sorb/Soil-Vigor, and the root watering system, which are on the way, I have everything else needed around my shop, just need to get some free labor out of my future son-in-law.  I do need to repair several of my existing radials thanks to my landscaper and will probably add some more.  I will post an update on my experience and results when done which will probably be a couple months from now. It might be a total waste of effort, or maybe not. Something to keep me busy though.

Jim

Jim Henry HBR Radio 1610, serving Honey Brook, PA. and NW Chester County.

http://www.airpower.com/HBR.htm

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