All antennas are two terminal devices.
There is no such thing as a single point feed antenna.

Changing a horizontal antenna to a vertical antenna at the same height
does not improve the radiation angle.
If it did everyone would have their horizontal antennas in the
vertical position.

AM radio stations depend on ground wave signals not sky wave.

A horizontal antenna theoretically does not have a ground wave so
verticals are used for AM stations as they produce a ground wave
signal.

For sky wave signals height is important in order to produce better
lower angle of radiation. Lower angle radiation provides longer hops.

Adjusting the height to adjust the impedance of the antenna is not to
be worried about. That's what matching systems are for.
With multielement antennas (beams) the feed point impedance can be
very low even if the antenna is high in the air. Some other means of
matching the antenna to the line is required.

Regards
Gary


On Sat, 03 Jan 2004 04:13:27 GMT, (Larry W4CSC) wrote:

On Fri, 02 Jan 2004 13:00:34 GMT, Shortwave Sportfishing
wrote:


Well, you kind of danced around the answer, but I'd still like to know
how the ground plane effects the radiation angle which logically would
also have an effect on reception of a signal. On page 3-9 of the ARRL
Antenna Handbook (16th addition - sorry, it's the latest I have at
hand at the moment) states:

On a vertical antenna that USES a ground plane, the radiation angle
increases towards straight up as the ground plane becomes "smaller",
electrically less efficient. On a half-wave, end-fed vertically
polarized antenna, where no ground plane is used as part of the
antenna design, I doubt you could measure any difference.

"The total current in the antenna consists of two components. The
amplitude of the first is determined by the power supplied by the
transmitter and the free-space radiation resistance of the antenna.
The second component is induced in the antenna by the wave reflected
by the ground. This second component, while considerably smaller than
the first at most usefull antenna heights, is by no means
insignificant."

Ham antennas, dipoles, beams, etc., used for HF communications are
HORIZONTALLY polarized antennas. This is a whole new ball game when
they are close to "ground" be it a sheet metal roof or the ground,
itself. Unlike the radiation pattern of the vertical halfwave in
question, the radiation pattern of a horizontal dipole, which is still
perpendicular to the dipole wire, INTERSECTS the ground plane below it
and the RF re-radiates or reflects off the ground plane. The
radiation pattern of a horizontal dipole very near ground is straight
up and has a hot-air-balloon shape straight up. As the antenna moves
away from ground, a dimple forms in the "balloon pattern" which forms
a null at zenith with the radiation now two "lobes", perpendicular to
the dipole whos angle of radiation drops from zenith out towards the
horizon as the dipole becomes 1/2 wavelength off ground. Beyond 1
wavelength off ground, the pattern becomes the familiar donut
perpendicular to the horizontal wire radiating upward and outward,
even down towards the ground plane, whos reflections and re-radiation
phase angles caused the odd pattern in the first place.

Vertically-polarized signals point the NULL in the radiation pattern
off the ends of the dipole. One of these nulls is towards the ground
plane so little re-radiation takes place. A 1/4 wavelength "ground
plane antenna" has a radiation pattern elevated only slightly towards
zenith, which isn't much of a problem at all.

So it would seem that the "ground plane/wave" is not an umimportant
consideration when considering antennas.

Ground effect is VERY important in a horizontally polarized dipole or
beam antenna. That's why we put the beams way up on towers so they
radiate towards the horizon, not at high radiation angles. The phase
shifted re-radiated patterns of the slightly longer reflector and
slightly shorter directors (lagging and leading, respectively) "pull"
the donut towards the directors and away from the reflector, pointing
the beam's radiation pattern in the desired, narrow direction....and
giving great gain.....if it's not too close to the ground, that is!

Further on that same page, is the following:

"Changing the height of the antenna above the ground will change the
current flow assuming that the power to the antenna is constant."

Again, this is for "ham antennas" which are generally horizontally
polarized. The reflected wave from the ground back to the horizontal
dipole GREATLY changes its impedance characteristics because that
reflected wave causes a phase shifted current in the radiating
element, itself. Close to ground, this creates a large REACTIVE
component, which shows up as reflected power at the transmitter
output, not good at all.

Again, it would appear that the "ground plane/wave" is not
insignificant.

Now, as I understand it, at VHF frequencies, the methodology of
providing energy to the antenna (loading/feed) is not as important to
the generation/reception of the signal as is height. In fact, if I
read the pattern charts correctly, the height of the antenna has more
to do with the lobe pattern (the donut you were discussing) than the
method of feeding the antenna.

Yes/No?

No, not on VERTICALLY polarized antennas.

On VHF there is no replacement for POWER and ALTITUDE. VHF is
line-of-sight communications. The higher the transmitter and receiver
antennas are, the longer your range and better your signal at the
longer range. It's why WCSC runs hundreds of kilowatts from a 2000'
tower.....RANGE. They pay very dearly for both. You should see the
WEEKLY electric bills and tower maintenance bills. On a skywave
system, like AM radio at night or ham radio HF, altitude is not very
important other than to make the antenna's radiation pattern and
impedance what we want because it's horizontal polarization.

On Mon, 05 Jan 2004 02:02:17 GMT, Gary Schafer
wrote:

All antennas are two terminal devices.
There is no such thing as a single point feed antenna.

Changing a horizontal antenna to a vertical antenna at the same height
does not improve the radiation angle.
If it did everyone would have their horizontal antennas in the
vertical position.

AM radio stations depend on ground wave signals not sky wave.

A horizontal antenna theoretically does not have a ground wave so
verticals are used for AM stations as they produce a ground wave
signal.

Hmm....I've been using horizontal antennas to transmit ground wave
communications since I was 11 years old in 1957!

All VHF and UHF TV stations use ground wave only signals and every one
of them in the USA are HORIZONTALLY POLARIZED. Kinda blows that
theory all to hell, doesn't it? Until very recently, all FM radio
stations were all horizontally polarized, too, but that was changed
because cars have vertically polarized antennas......or did when they
changed the rules. Embedded FM antennas in windshields are
horizontally polarized, a dipole.

For sky wave signals height is important in order to produce better
lower angle of radiation. Lower angle radiation provides longer hops.

Depends on how far you wish to talk. I use very high angles of
radiation on 3915 Khz to talk to my buddies around SC, NC and Georgia
on 75 meters. This is easily possible because my inverted-V dipole is
only up about 30', not much % of a wavelength when the wavelength is
240 feet long. Listen from 3.5 to 4.0 Mhz nights and 7.0-7.3 Mhz days
and hear lots of us "high-angle-radiators" shooting the breeze, ad
nauseum. Works great since 1957....(c;

Adjusting the height to adjust the impedance of the antenna is not to
be worried about. That's what matching systems are for.
With multielement antennas (beams) the feed point impedance can be
very low even if the antenna is high in the air. Some other means of
matching the antenna to the line is required.

Absolutely nothing radiates like a TUNED antenna, without the lossy
tuner between feedline and antenna. Damned Navy has tuners so
inefficient trying to load a flagpole whip they have to have BLOWERS
in them to keep from melting them. All that power ISN'T radiated,
obviously.

I used to operate WB4THE/MM2 when I was a young sailor on USS
Everglades (AD-24) back in the 60's. It was my call at that time. My
captain never got over I could make phone patches to his wife back in
Charleston through a friend of mine on James Island (K4OKD) with my
$249 Heathkit HW-100 kit transceiver, even barefoot, when the Navy's
million-dollar radio installation wouldn't. He used to tease the comm
officer by saying to him, "I want to talk to Charleston. Can we do
that?" Of course, the answer was no. "That's BS. I just talked to
my wife on ET1 Butler's ham radio not 10 minutes ago! What's wrong
with our radios?"

The comm officer hated my guts.....and said so...(c; They used to
listen to my homebrew quad 813s linear amp up in radio when the old
man was on the air. The chief radioman used it, too....

Regards
Gary

73 DE W4CSC/MM2
Watch out for those ground waves.....(c;

On Tue, 06 Jan 2004 06:11:17 GMT, (Larry W4CSC) wrote:

On Mon, 05 Jan 2004 02:02:17 GMT, Gary Schafer
wrote:

All antennas are two terminal devices.
There is no such thing as a single point feed antenna.

Changing a horizontal antenna to a vertical antenna at the same height
does not improve the radiation angle.
If it did everyone would have their horizontal antennas in the
vertical position.

AM radio stations depend on ground wave signals not sky wave.

A horizontal antenna theoretically does not have a ground wave so
verticals are used for AM stations as they produce a ground wave
signal.

Hmm....I've been using horizontal antennas to transmit ground wave
communications since I was 11 years old in 1957!

All VHF and UHF TV stations use ground wave only signals and every one
of them in the USA are HORIZONTALLY POLARIZED. Kinda blows that
theory all to hell, doesn't it? Until very recently, all FM radio
stations were all horizontally polarized, too, but that was changed
because cars have vertically polarized antennas......or did when they
changed the rules. Embedded FM antennas in windshields are
horizontally polarized, a dipole.

For sky wave signals height is important in order to produce better
lower angle of radiation. Lower angle radiation provides longer hops.

Depends on how far you wish to talk. I use very high angles of
radiation on 3915 Khz to talk to my buddies around SC, NC and Georgia
on 75 meters. This is easily possible because my inverted-V dipole is
only up about 30', not much % of a wavelength when the wavelength is
240 feet long. Listen from 3.5 to 4.0 Mhz nights and 7.0-7.3 Mhz days
and hear lots of us "high-angle-radiators" shooting the breeze, ad
nauseum. Works great since 1957....(c;

Adjusting the height to adjust the impedance of the antenna is not to
be worried about. That's what matching systems are for.
With multielement antennas (beams) the feed point impedance can be
very low even if the antenna is high in the air. Some other means of
matching the antenna to the line is required.

Absolutely nothing radiates like a TUNED antenna, without the lossy
tuner between feedline and antenna. Damned Navy has tuners so
inefficient trying to load a flagpole whip they have to have BLOWERS
in them to keep from melting them. All that power ISN'T radiated,
obviously.



TV and FM stations do not depend on ground wave propagation. It is
line of sight. Nothing to do with polarization or ground wave.

FM stations have had dual polarization (both horizontal and vertical)
for many years. Only because cross polarization with the receiving
antenna greatly attenuates the signal.

Ground wave propagation as in AM stations is not a sky wave. It
follows the curvature of the earth staying close to the ground (ground
wave).

A horizontal antenna does not produce any significant ground wave.
(wave that stays close to the earth) The ground wave from a horizontal
antenna will fall off in just a few miles.

Yup that's what I said. "For sky wave signals height is important in
order to produce better lower angle of radiation. Lower angle
radiation provides longer hops."

The propagation that you experience on 80 and 40 meters with the guys
around the state is the result of high angle radiation and reflections
as you state.

If you want higher angle, shorter hops, keep the antenna low.


Tuned antenna? I assume you are referring to a "resonant antenna"?

A non resonant antenna radiates just as well as a resonant antenna.
Only difference is the impedance presented to the feed line. But even
a resonant antenna may not provide 50 ohms to your coax. Depends on
how high it is. :)

Regards
Gary

On Tue, 06 Jan 2004 18:17:04 GMT, Gary Schafer
wrote:

TV and FM stations do not depend on ground wave propagation. It is
line of sight. Nothing to do with polarization or ground wave.

Gary, maybe you can help me out with something here, because either
I've forgotten or I was taught incorrectly.

Over short distances (Up to five to eight miles), the ground wave
component of any VHF signal is actually the primary method by which
VHF signals are received and not by Line Of Sight.

Not true?

Later,

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

St. Pete, 12 Lb. Test

On Tue, 06 Jan 2004 22:11:54 GMT, Shortwave Sportfishing
wrote:

On Tue, 06 Jan 2004 18:17:04 GMT, Gary Schafer
wrote:

TV and FM stations do not depend on ground wave propagation. It is
line of sight. Nothing to do with polarization or ground wave.

Gary, maybe you can help me out with something here, because either
I've forgotten or I was taught incorrectly.

Over short distances (Up to five to eight miles), the ground wave
component of any VHF signal is actually the primary method by which
VHF signals are received and not by Line Of Sight.

Not true?

Later,

Tom
S. Woodstock, CT


I don't think so. There is some bending, refraction of the signal that
makes the VHF radio horizon slightly longer than line of sight but it
is due to the atmosphere and not ground wave propagation.

If you have a VHF station on a high mountain peak or a very high tower
there could be no ground effect at all.

Regards
Gary

On Tue, 06 Jan 2004 22:32:30 GMT, Gary Schafer
wrote:

On Tue, 06 Jan 2004 22:11:54 GMT, Shortwave Sportfishing
wrote:

On Tue, 06 Jan 2004 18:17:04 GMT, Gary Schafer
wrote:

TV and FM stations do not depend on ground wave propagation. It is
line of sight. Nothing to do with polarization or ground wave.

Gary, maybe you can help me out with something here, because either
I've forgotten or I was taught incorrectly.

Over short distances (Up to five to eight miles), the ground wave
component of any VHF signal is actually the primary method by which
VHF signals are received and not by Line Of Sight.

I don't think so. There is some bending, refraction of the signal that
makes the VHF radio horizon slightly longer than line of sight but it
is due to the atmosphere and not ground wave propagation.

If you have a VHF station on a high mountain peak or a very high tower
there could be no ground effect at all.

You are making me unpack my reference books now. :)

Later,

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

St. Pete, 12 Lb. Test

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.


In line of sight communications there are reflections from the earth
or other objects that can add or subtract to the signal that is being
received directly. The reflected signal gets shifted 180 degrees as it
is reflected. At VHF the reflected wave (because it is rather short
compared to the distances involved) can shift rapidly in phase. This
is what causes flutter on the signal at times.

With horizontal polarization at low HF the wave length is long
compared to the distances involved in the direct and ground reflected
waves. They arrive almost always 180 degrees out of phase. That highly
attenuates the direct wave signal.

NO SURFACE WAVE FROM HORIZONTAL ANTENNAS: from ARRL antenna handbook.

With a vertical antenna the electric field is perpendicular to the
ground. It is a law of electromagnetics that electric lines must touch
a conductor (the earth in this case) perpendicular or else they would
have to generate infinite currents in the conductor. The earth is a
rather good conductor below about 10 mhz so waves at these frequencies
are mainly vertical when traveling close to the ground. If they were
horizontal they would try to induce large currents and be absorbed by
the earth. They get shorted out.

This is why a horizontal antenna has little ground wave or surface
wave. It dies out very rapidly. In addition horizontally polarized
direct waves at low HF get canceled by ground reflections. (see above)

Thus the reason for vertical AM broadcast antennas.

At VHF antenna heights are usually several wavelengths above ground
and polarization does not matter. Plus the earth is not a good
conductor as to short out the horizontal waves as it does at low HF.

The reason for vertical polarization being mostly used at VHF is it is
much easier to obtain omni coverage with simpler antennas. Especially
portable and mobile antennas.

Regards
Gary

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