The reason for ground losses is because the ground is not a perfect
conductor. Just like any metal it has some resistance (lots more than
any metal), and anytime an electric field interacts with it there is
some heating due to that resistance. A radio wave does not reflect off
the top of the soil, it penetrates some distance in(go read about skin
depth), and as it penetrates into the soil the electric field moves ions
in the ground which generate heat. This does not just apply for
verticals, it also happens for horizontal antennas and even at the far
distance point where your signal that has reflected off the ionosphere
comes down again and reflects off the earth for its next hop.
David Robbins K1TTT
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: firstname.lastname@example.org [mailto:towertalk-
> email@example.com] On Behalf Of Al Williams
> Sent: Saturday, December 04, 2004 17:43
> To: Towertalk
> Subject: Re: [TowerTalk] elevated short vertical dipole or
> ----- Original Message -----
> >. Did you ever contemplate where the difference was coming from?
> > Ground losses?
> I have difficulty in understanding or accepting the notion of "ground
> losses--...wasted power heating the earth, etc..."
> I have no problem with using a dc, ac, or rf resistance meter to
> between two earth points, but radio waves striking the earth, I dunno!
> What follows is what is puzzling; maybe someone can help answer them.
> 1. Radio waves from a horizontal antenna striking the ground are
> reflected (exactly what is going on by reflection?) and add signal
> strength to the skyward wave. However radio waves from a 1/4 wave
> vertical striking the ground are absorbed (all? partially ? and as a
> result do not provide the ~2 db gain of a dipole and the ~ 4 db gain
> from ground "reflection".
> 2. The horizontal dipole radiates because each half of the dipole
> alternately charges and discharges oppositely and equally. But what
> goes on when the feedpoint is moved off center so that metal to charge
> on each side is unequal?
> 3. The 1/4 vertical alternately charges the vertical portion against
> ground (or ground wires, salt water). Therefore is the problem not
> the ground is lossy but rather that the vertical part of the antenna
> cannot be charged as well it is over metal wires or salt water? Has
> anyone measured the power going into the vertical part when over
> vs when over wires or salt water?
> 4. Is the "ground loss" frequently referred to related or confined to
> the Brewster angle consideration?
> 5. Again, what is actually going on by ionosphere and ground
> reflection--is it similar to metal interception radio waves and
> a generator?
> See: http://www.mscomputer.com for "Self Supporting Towers",
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041
> any questions and ask for Sherman, W2FLA.
> TowerTalk mailing list
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
TowerTalk mailing list