On Wed, 07 Jan 2004 02:31:17 GMT, Gary Schafer
wrote:

Some clarification of "ground wave" is in order here. The term ground
wave is sometimes lumped into several different modes that are not
"sky wave" modes.

SURFACE WAVES:

The ground wave that I am referring to here is sometimes called
"surface wave". It is in the ground wave family.
A surface wave travels close to the ground actually touching the
ground. AM radio stations depend on this method of propagation. At AM
frequencies it is good out to about 100 miles. The signal strength is
quite weak at that distance. But in the shorter distances it provides
a very reliable and predictable constant coverage. Unlike sky wave
signals that come and go between night and day.

At higher frequencies that distance is much shorter as the signal gets
highly attenuated. So "surface waves" are not very useful at
frequencies much above the broadcast band for any significant
distance.

The old 2 MHZ marine band used to depend on "surface wave"
communication. With good conditions range can be better than VHF but
usually quite noisy on those frequencies. Also a more complicated
antenna system was needed and higher power than what is used on VHF.

DIRECT WAVES:

Line of sight propagation is also a form of ground wave propagation in
that it does not become a sky wave and reflect off the upper
atmosphere. It may follow the earths curvature and may or may not
touch the earth. This type of propagation is commonly called "direct
wave".

As you asked about "the ground wave component of VHF signals being the
primary method by which VHF signals are received and not by line of
sight".

The primary method is by line of sight which is technically a form of
ground wave as explained above. But usually when someone mentions
"ground wave" they are usually referring to "surface wave".
Line of sight is usually used when referring to "direct wave" VHF
communications.

~~ snippage ~~

Thank you. :)

Later,

Tom
S. Woodstock, CT
----------
"My rod and my reel - they comfort me."

St. Pete, 12 Lb. Test