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Mikefromms
Intermediate Member
Username: Mikefromms
Post Number: 303
Registered: 6-2003
| | Posted on Monday, November 29, 2004 - 8:23 pm: | 
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I've been referred to you to answer a question about my dipole that is strung out over a concrete drive and working extra fantastic. The dipole is half slanted and the bottom part is almost vertically hanging down. The bottom wire is about 10 ft off the concrete drive and the top, well...about 26 ft. The antenna is transmitting and receiving extra good. The reports are always good. Just wondering if the concrete is forming some type of groundplane that is making my signal extra strong?
Thanks,
Mikefromms |
Tech833
Moderator
Username: Tech833
Post Number: 896
Registered: 8-2002
| | Posted on Tuesday, November 30, 2004 - 10:02 am: |
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Hi Mike.
Yes and no.
Your dipole is a balanced antenna (unlike an A99 or Imax, etc.) and you will naturally develop a lower takeoff angle at the same elevation with it. However, the concrete likely has wire mesh in it and if there is some connection (or capacitive coupling) to the wire mesh, you can increase your ground conductivity as long as the ground under the concrete pad remains conductive.
I use a similar ground system at my home. I have a cement slab under my home and outbuildings. The slab has bonded wire mesh on the dirt with copper wires across it before the conrete was poured. Those copper wires are all bonded at the tower end. The far end extendes beyond the concrete in all directions and continues on to the property lines (several hundred feet on some of them). The concrete does not really 'add' any grounding, but it does form a better capacitive bond with the ground under the buildings than I otherwise would have achieved. In very dry non-conductive earth, this will gain you almost nothing. In conductive ground, this will gain you a lot.
The short answer can be found in the design of other balanced antennas or 'upside down' antennas like the Top One or the GAP multiband ham antennas.
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