Frank wrote:
. . .
I agree with comments about adding a horizontal wire to the top of the
vertical; it will probably be easier than a capacity hat. I am overloaded
with work at the moment, but would like to attempt a model in a week or so
when I have less work.

Take a look also at a tee type arrangement. That is, a horizontal wire
with the tip of the vertical connected at or near its center. It might
have some advantages over connecting the wire's end to the vertical. But
of course it might be more involved to construct.

Roy Lewallen, W7EL

Dan, KB0QIL wrote:
"From a practical perspective it would seem to me that building a 40
foot crnter loaded dipole and putting it in the sttic or on the roof
would probably perform somewhat better."

The roof or attic may be noisy receiving locations.

The ionospheric spot which effectively reflects a high frequency signal
to a point beyond the horizon is variable so that the received signal
direction varies from the true bearing of the transmitter, The received
signal elevation angle also varies from that predicted by the assumed
layer height for any given path length, and may change from instant to
instant.

The differences between predicted and actual azimuth and elevation
angles may at any momement be several degrees. These differences make
high frequency direction finding complicated, but results may be good
enough for some pracical purposes. Optimum vertical and horizontal
angles are sought in directional antenna design but enough beamwidth is
needed to accommodate
the angular variations which occur.

Over sea water, ground wave propagation is good and loss is low as
compared with propagation over earth. Frequencies up to about 5 MHz are
used for communications beyond the line of sight between ships and
between ships and shore. These frequencies are also used for tropical
broadcasting among islands.

For ionospheric reflection to near spots beyond the line of sight, near
vertical incidence reflections are used. The frequency must be below the
maximum usable frequency for vertical incidence at the transmitting
site.

For ground wave propagation a vertical transmitting antenna is used.

Horizontally polarized antennas are often used for sky wave signals
because reflection from the ionosphere makes equal strength components,
horizontally polarized and vertically polarized, from the incident wave,
regardless of its initial polarization.

Most disturbing noise is that generated within ground wave range of the
receiving antenna. It is vertically polarized.There is no ground wave
propagation of horizontally polarized waves. Thus, a horizontally
polarized receiving antenna ignores much of the available noise.
However, it receives as much signal from the sky wave as a vertically
polarized antenna would.

If a single antenna is to be used for both transmitting and receiving a
shy wave, a forizontally polarized antenna may be the better choice due
to its noise rejection. See "Radio Antenna Engineering" by Edmund A.
Laport for details.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote in message
...
Dan, KB0QIL wrote:
"From a practical perspective it would seem to me that building a 40
foot crnter loaded dipole and putting it in the sttic or on the roof
would probably perform somewhat better."

The roof or attic may be noisy receiving locations.

The ionospheric spot which effectively reflects a high frequency
signal
to a point beyond the horizon is variable so that the received
signal
direction varies from the true bearing of the transmitter, The
received
signal elevation angle also varies from that predicted by the
assumed
layer height for any given path length, and may change from instant
to
instant.

The differences between predicted and actual azimuth and elevation
angles may at any momement be several degrees. These differences
make
high frequency direction finding complicated, but results may be
good
enough for some pracical purposes. Optimum vertical and horizontal
angles are sought in directional antenna design but enough beamwidth
is
needed to accommodate
the angular variations which occur.

Over sea water, ground wave propagation is good and loss is low as
compared with propagation over earth. Frequencies up to about 5 MHz
are
used for communications beyond the line of sight between ships and
between ships and shore. These frequencies are also used for
tropical
broadcasting among islands.

For ionospheric reflection to near spots beyond the line of sight,
near
vertical incidence reflections are used. The frequency must be below
the
maximum usable frequency for vertical incidence at the transmitting
site.

For ground wave propagation a vertical transmitting antenna is used.

Horizontally polarized antennas are often used for sky wave signals
because reflection from the ionosphere makes equal strength
components,
horizontally polarized and vertically polarized, from the incident
wave,
regardless of its initial polarization.

Most disturbing noise is that generated within ground wave range of
the
receiving antenna. It is vertically polarized.There is no ground
wave
propagation of horizontally polarized waves. Thus, a horizontally
polarized receiving antenna ignores much of the available noise.
However, it receives as much signal from the sky wave as a
vertically
polarized antenna would.

If a single antenna is to be used for both transmitting and
receiving a
shy wave, a forizontally polarized antenna may be the better choice
due
to its noise rejection. See "Radio Antenna Engineering" by Edmund A.
Laport for details.

Best regards, Richard Harrison, KB5WZI

================================

Richard,

I am impressed by your logical descriptions and explanations of
skywave and groundwave propagation. You are more than convincing. No
doubt reinforced from practical experience. It all makes sense.
Something much needed on these newsgroups.

I notice you do not treat the works of so-called 'experts' as bibles
but as a means of further study.
----
Reg, G4FGQ

Roy,

Thanks. This might be feasible. The site would support 50 foot wire from the
tip. At 500 watts what would the current in the horizontal leg be? In other
words what is the minimum effective gage?

What is the purpose of this leg? Is it capacitive or does it begin to look like
something else. What are it directional characteristics? Dipoles nodes are
perpendicular while long wire nodes are parallel.

Dan

Roy Lewallen wrote:
Frank wrote:

. . .
I agree with comments about adding a horizontal wire to the top of the
vertical; it will probably be easier than a capacity hat. I am
overloaded with work at the moment, but would like to attempt a model
in a week or so when I have less work.


Take a look also at a tee type arrangement. That is, a horizontal wire
with the tip of the vertical connected at or near its center. It might
have some advantages over connecting the wire's end to the vertical. But
of course it might be more involved to construct.

Roy Lewallen, W7EL

To determine the horizontal wire current, download the free EZNEC demo
from http://eznec.com. That's exactly the kind of thing it's good for.

If you put a single horizontal wire out to make an L shape, the wire
radiates a considerable amount. Being as low as it is, a lot of the
power will be dissipated in the ground, and only a small fraction will
be radiated at a low elevation angle. But if you connect to the center
of a horizontal wire to make a T shape, the fields from the two halves
of the horizontal wire will nearly cancel, so it'll radiate very little.
Its main effect, like a capacitive top hat, will be to even out the
current in your vertical wire, which will raise the radiation resistance
and therefore the efficiency.

EZNEC or a similar program will quickly show you the differences in
field strength in various directions for the antenna as it is, and with
either of the top loading configurations.

Roy Lewallen, W7EL

dansawyeror wrote:
Roy,

Thanks. This might be feasible. The site would support 50 foot wire from
the tip. At 500 watts what would the current in the horizontal leg be?
In other words what is the minimum effective gage?

What is the purpose of this leg? Is it capacitive or does it begin to
look like something else. What are it directional characteristics?
Dipoles nodes are perpendicular while long wire nodes are parallel.

Dan

Roy Lewallen wrote:

Frank wrote:

. . .
I agree with comments about adding a horizontal wire to the top of
the vertical; it will probably be easier than a capacity hat. I am
overloaded with work at the moment, but would like to attempt a model
in a week or so when I have less work.



Take a look also at a tee type arrangement. That is, a horizontal wire
with the tip of the vertical connected at or near its center. It might
have some advantages over connecting the wire's end to the vertical.
But of course it might be more involved to construct.

Roy Lewallen, W7EL

There is no ground wave
propagation of horizontally polarized waves. Thus, a horizontally
polarized receiving antenna ignores much of the available noise.

There can be exceptions to this though. There is a horizontal "space
wave" and it can cause all kinds of noise problems. In fact, I have
had just as much noise problems with horizontal dipoles, as I have
with verticals. Much of the local noise here is power line noise.
The lines are horizontal in general, and do emit a horizontaly
polarized
space wave which can travel a fair piece. I've found at this qth,
polarization and noise don't always follow the expected norms.
I've had horizontal antennas that picked up horrible amounts of noise.
But....On the bright side...it does verify that they are working... :/

Here in the cement jungle, I think noise can be about any polarization
depending on the source. Some is vertical, but just as much is also
horizontal. Of course, being vertical can follow a true ground wave
type of propogation, I would expect vertical noise to travel farther
than horizontal if you exceeded the direct line of sight. MK

I think Roy is referring to a T configuration rather than an upside-down L.
The currents will balance in the T so wire size is limited by physical
considerations rather than electrical. This is just another form of a
capacity hat. The net result is to raise the radiation resistance.

"dansawyeror" wrote in message
...
Roy,

Thanks. This might be feasible. The site would support 50 foot wire from
the
tip. At 500 watts what would the current in the horizontal leg be? In
other
words what is the minimum effective gage?

What is the purpose of this leg? Is it capacitive or does it begin to look
like
something else. What are it directional characteristics? Dipoles nodes are
perpendicular while long wire nodes are parallel.

Dan

Roy Lewallen wrote:
Frank wrote:

. . .
I agree with comments about adding a horizontal wire to the top of the
vertical; it will probably be easier than a capacity hat. I am
overloaded with work at the moment, but would like to attempt a model
in a week or so when I have less work.


Take a look also at a tee type arrangement. That is, a horizontal wire
with the tip of the vertical connected at or near its center. It might
have some advantages over connecting the wire's end to the vertical. But
of course it might be more involved to construct.

Roy Lewallen, W7EL

Fred W4JLE wrote:
I think Roy is referring to a T configuration rather than an upside-down L.
The currents will balance in the T so wire size is limited by physical
considerations rather than electrical. This is just another form of a
capacity hat. The net result is to raise the radiation resistance.

In a tee type antenna, there will be considerable current at the
junction of the horizontal and vertical wires. While it's unlikely that
any wire strong enough to be used won't be able to handle the current
from a heating standpoint, it is possible that using a wire on the small
end of the range might result in noticeable loss. A quick run with a
modeling program would show whether or not that might happen with a
given set of dimensions.

One thing I should mention. If the horizontal portion is higher than
about 0.2 wavelength, MININEC-type ground can be used for modeling
either a T or L. The vertical wire is connected directly to ground, and
ground loss can be inserted at the base as a resistive load. If the
horizontal wire is much less than 0.2 wavelength high, the MININEC-type
ground can still be used with reasonable accuracy only for the T type
antenna. For an L type antenna where the horizontal wire is less than
0.2 wavelength high, a model has to use the High Accuracy ground model,
with the ground system modeled as radial wires just above the ground.

Roy Lewallen, W7EL

Mark Keith, NM5K wrote:
"I`ve had horizontal antennas that picked up horrible amounts of noise."

Yes, the protectection comes from noise beyond the line of sight range
but not so far away as to require aky wave propagation.

Propagation is a function of frequency. Below 100 KHz, gtound waves are
little affected by the earth`s attenuation and the sky wave is reflected
with little loss by the ionosphere. Waves travel up to 600 miles with
little perturbation from the time of day, season, or year, but at
greater distances, low frequency reception is better at night and in the
winter due to ionospheric changes affecting the reflected signal.. On a
yearly basis, signal strength over long distances correspond with the
11-year sunspot cycle. Low frequency signal strength changes only slowly
without rapid fades which characterize high frequency operation.

At frequencies above 100 KHz but below 535 KHz, ground wave attenuation
is greater than at frequencies below 100 KHz. Daytime ionospheric losses
are very high. Daytime ground wave propagation is better at the lower
end of this frequency range and over soil of higher conductivity.
Signals may extend to several hundred miles, where noise levels in the
receiving location are low. Nighttime transmission to distant points is
possible due to ionospheric reflection. Dependable daytime reception in
the 100 to 535 KHz range is bad due to lack of ionospheric propagation
and high attenuation of the ground wave especially at the higher
frequency end of this band over poorly conductive earth and during the
summer months when there may be thunder storms producing static eithin
ground wave range..

At frequencies between 535 KHz and 1600 KHz, only the ground wave is
useful in the daytime beyond the line of sight, as the sky wave is
completely absorbed. The higher the frequency in this range, and the
poorer the earrth`s conductivity,, the greater the attenuation of the
ground wave. High powered transmitters at the lower frequencies in this
range reach 50 to 100 miles over high conductivity soil. This may be
pessimistic. I listen 24 hours to 50 KW KKYX in San Antonio which is 200
miles to my west satisfactorily. It broadcasts on 680 KHz. My receivers
are quite ordinary and use internal loop antennas. The earth is highly
conductive but there is no sea water in the path. At night, other
stations
produce low frequency carrier beats with KKYX causing undesirable
automatic volume control action. but KKYX`s sky wave is stronger than
its groundwave and its reception is still acceptable.. Radio Havana is
one of its competitors. I hear all about "El Comandante" at times.

Sky wave goes far in the 535 to 1600 KHz band. During Hurricane Carla in
the 1960`s I listened to Dan Rather describe the storm blow by blow on
KTRH, Houston`s 50 KW outlet, from Tierra del Fuego where I was working,
and listening on a Hitachi pocket transistor portable radio with its
built in loop antenna. The path is about 6000 miles long but mostly over
the ocean. KTRH transmits on 740 KHz from the banks of Cedar Bayou. They
have a 4-tower directionnal array with a North-South bias. Reception was
good in Tierra fel Fuego as it is nearly at the Antarctic Circle and
there are no thunder storms there. It is too cold. Groundwave extends
hundreds of miles from KTRH, but not 6000 miles. My reception was shy
wave using several hops.. Broadcast transmitters concentrate energy
along the horizon so low elevation angles are favored.. This works well
for sky wave DX, especially over the ocean.

Sky wave attenuation in the 535 to 1600 KHz band is about the same
throughout the band, so nighttime coverage of broadcast stations in this
range is almost independent of frequency, while daytime ground waves
favor the lower frequencies. When I was a kid, I had a crystal set fixed
tuned to KTRH which directly drove a loudspeaker, if I could find a
sensitive spot on the galena. I lived almost in sight of the station.

At frequencies between 1600 KHz and 30 MHz, the ground wave attenuates
so rapidly as to be usseless except over very short distances.
Propagation is either line of sight or via ionospheric reflection or via
tropospheric scattering. Frequencies above 30 MHz are often used for
scattering ao that extremely high gain antennas are practical.
Scatterihg often uses brute force to extend the range of signals beyond
the line of sight.

Most long-distance short-wave communications result from ionnospheric
reflection. In the frequency range of 1600 KHz to 30 MH, a band of
frequencies can almost always be found that provides communications by
sky wave over a path between two points on earth.

The maximum usable frequency depends on the distance between the points
and ionospheric conditions. The minimum usable frequency depends on
ionospheric conditions, effective radiated power, and the noise level at
the receiver. Losses in the ionosphere increase with wavelength, so the
frequency which gives the best signal is usually the maximum usable
frequency. For communocations reliability, the maximum usable frequency
is often discounted by 15% to provide an "Optimum Working Frequency".

Daytime DX requires a high frequency. Shorter paths require lower
frequencies.

Typically 10 to 29 MHz during the day and 5 to 10 MHz, at night, are
best for transmission over transoceanic distances (thousands of miles).
Rember the Zenith portable? The best frequencies are usually higher
during the day for long paths than they are at night

Optimum frequency increases with the length of the path up to the
maximum distance for one-hop transmission, about 1200 to 2400 miles. Low
elevation-angle radiation such as 5 to 15 degrees is usually most
desirable. Radiation below an angle of about 3.5 degrees may be
absorbed by the earth near the transmitting antenna and wasted.

Frequencies above 30 MHz are usually not reflected by the ionosphere and
provide only sporadic sky wave communications.

Best regards, Richard Harrison, KB5WZI

Now that is interesting, Roy. I was going to put up a 160 m inverted L this
summer. I am limited to only being able to go up about 45 feet, so I would
need about another 90 feet horizontal.

Are you suggesting that it might be a better arrangement to go up the 45'
and then put up the top "T"? If so, roughly how long should the top part of
the T be (each side of center) to get me to 160? I'm guessing it may not be
accomplished without some base loading...and that is what took me to the
Inverted L in the first place...direct coax feed, albeit not a particularly
good low angle radiator.

I am prepared to put down a radial field...but I want to stick with a simple
vertical wire, either extended horizontally as an Inverted L or as you
suggest, a T, if it can be done. I have about 100' either side of center
available to construct the top part of the T. In either case, the top
loading wires will need to be somewhat of the inverted v construction, as I
don't have 45' high supports for each end.

Thanks for any thoughts you might have. I need to get something done before
winter!

73,

....hasan, N0AN

"Roy Lewallen" wrote in message
...
To determine the horizontal wire current, download the free EZNEC demo
from http://eznec.com. That's exactly the kind of thing it's good for.

If you put a single horizontal wire out to make an L shape, the wire
radiates a considerable amount. Being as low as it is, a lot of the power
will be dissipated in the ground, and only a small fraction will be
radiated at a low elevation angle. But if you connect to the center of a
horizontal wire to make a T shape, the fields from the two halves of the
horizontal wire will nearly cancel, so it'll radiate very little. Its main
effect, like a capacitive top hat, will be to even out the current in your
vertical wire, which will raise the radiation resistance and therefore the
efficiency.

EZNEC or a similar program will quickly show you the differences in field
strength in various directions for the antenna as it is, and with either
of the top loading configurations.

Roy Lewallen, W7EL

dansawyeror wrote:
Roy,

Thanks. This might be feasible. The site would support 50 foot wire from
the tip. At 500 watts what would the current in the horizontal leg be? In
other words what is the minimum effective gage?

What is the purpose of this leg? Is it capacitive or does it begin to
look like something else. What are it directional characteristics?
Dipoles nodes are perpendicular while long wire nodes are parallel.

Dan

Roy Lewallen wrote:

Frank wrote:

. . .
I agree with comments about adding a horizontal wire to the top of the
vertical; it will probably be easier than a capacity hat. I am
overloaded with work at the moment, but would like to attempt a model
in a week or so when I have less work.



Take a look also at a tee type arrangement. That is, a horizontal wire
with the tip of the vertical connected at or near its center. It might
have some advantages over connecting the wire's end to the vertical. But
of course it might be more involved to construct.

Roy Lewallen, W7EL