On Sat, 20 Aug 2005 13:34:36 -0500, Cecil Moore wrote:
dansawyeror wrote:
I will defiantly try adding radials.

Who are you defying?

Lawn gnomes, probably.

The local gardener who takes great pride and ownership in the lawn. The garage
can go mostly to seed, however the lawn must be pristine. Each antenna change
meets with great resistance. Although defiantly was definitely a spell checker
choice, it is also the correct one for getting radials.

Dan

Cecil Moore wrote:
dansawyeror wrote:

I will defiantly try adding radials.


Who are you defying?

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Hello Dan,

Some thoughts:

The 10 dB loss is, of course, referenced to a "perfect ground." Even
with a full length (quarter-wave) vertical and your ground system,
performance would improve by about 3 dB. Not a blockbuster.

Improving the radial system, as noted by others, is a more realistic
course. You ought to be able to get the ground resistance closer to 20
ohms with more radials close in. Then you will be only 6 dB worse than
if your ground were perfect.

Putting up an indoor dipole is cheap and quick. Put it up and compare it
with the vertical. But don't hold your breath. You will probably find
that with some paths, the dipole is better. you may want to keep both.

I assume you've ruled out a capacity hat, center loading, and a coil
with lower losses, as suggested by others. But with these changes and an
improved ground system, you might get a full (6 dB) S-unit improvement.

Good luck.

73,

Chuck





dansawyeror wrote:
All,

I have been using an 80 meter loaded vertical for a couple of years with
moderate success. The ground system is a dozen 'untuned' radials 40 or
so feet laying on the ground. The feed line is about 100 feet of RG-8
coax. The SWR in the shack is about 1.1 to 1.

I have done some research on the antenna and based on it parameters it
should have a radiation resistance of about 4 Ohms. This says that the
coil and ground are absorbing on the order of 45 Ohms. This is 10db
performance loss.

I have limited space and the most common solutions are not available to
me. From a practical perspective it would seem to me that building a 40
foot center feed loaded dipole and putting it in the attic or on the
roof would probably perform somewhat better.

Is this a reasonable assumption?

Would burying the radials and connecting them to several 4 square foot
buried screens substantially help the ground system?

Thanks,
Dan kb0qil

dansawyeror wrote:
All,

I have been using an 80 meter loaded vertical for a couple of years with
moderate success. The ground system is a dozen 'untuned' radials 40 or
so feet laying on the ground. The feed line is about 100 feet of RG-8
coax. The SWR in the shack is about 1.1 to 1.

I have done some research on the antenna and based on it parameters it
should have a radiation resistance of about 4 Ohms. This says that the
coil and ground are absorbing on the order of 45 Ohms. This is 10db
performance loss.

I have limited space and the most common solutions are not available to
me. From a practical perspective it would seem to me that building a 40
foot center feed loaded dipole and putting it in the attic or on the
roof would probably perform somewhat better.

Is this a reasonable assumption?


I'm not sure you can count on that. You'd still lose some in a
matching/loading network, there'd be a lot of ground loss because of the
low height, and absorption of some of the power from conductors in the
house might occur. It wouldn't hurt to try, but leave your vertical up.

Would burying the radials and connecting them to several 4 square foot
buried screens substantially help the ground system?

Just about anything you can do to increase the conductivity of the
ground system, particularly close to the antenna, will help. Using
screen is one thing. Burying the radials won't help. Adding more radials
and making them longer will help. Unfortunately, making a few radials
longer doesn't do much, and adding a bunch of short radials doesn't do
much either -- you really have to do both to have a big effect. If
possible, connect to any other nearby buried conductors such as metallic
water pipes.

The other thing you can do to improve the efficiency is to increase the
radiation resistance of the antenna. You can do this of course by
increasing the height of the antenna. Moving the loading coil upward
will help, too, although you'll need more inductance. (The coil still
won't be a major part of the overall loss, though.) A top hat is better
yet. You can also increase the radiation resistance by making your
antenna fatter. Use multiple wires in parallel, spaced about as far as
you can, either along side each other, or fanned out, converging at the
bottom.

Finally, if you've got room, you can improve your overall efficiency by
about 3 dB by putting in another identical antenna/ground system
somewhere nearby and connecting the two in parallel.

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

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

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