On Wed, 17 May 2006 17:10:00 GMT, Cecil Moore
wrote:

Yuri Blanarovich wrote:
I have seen situations when signals to Europe were coming under low angle
and in the same direction, signals to deep Asia were coming under higher
angle at the same time.

Seems to me a rotatable dipole with the ability to also
rotate from horizontal to vertical would be a good thing
to have.

or tie two together in a vertical/horizontal phased array?
--
73 for now
Buck
N4PGW

"Yuri Blanarovich" wrote in message
...
Reg wrote:
The type of antenna or its radiation pattern has nothing whatever
to
do with the path taken by the radio wave through the ionosphere.
The
take-off angle and its name, generated by EZNEC, can be very
misleading.


It has to do. It allows us to direct the RF under desired angle to
hit the
layer or region that supports the propagation to the chosen target.
=========================================
Yuri,

The elevation angle of the radio path from the transmitter on its way
to the target changes with the number of hops.

How does Eznec know the number of hops? How does Eznec know which
angle is correct? How does Eznec know the height of the reflecting
layers? How does Eznec know the distances at which the radio wave
returns to Earth to be re-reflected?

Eznec doesn't know. And neither does the radio operator unless he
estimates everything AFTER the event.

Radio waves follow paths dictated by trigonometry and geometry and are
entirely independent of the idiosyncrasies of radio antennas.
----
Reg.

On Wed, 17 May 2006 20:15:24 +0100, "Reg Edwards"
wrote:

The elevation angle ... changes
....
Radio waves follow paths dictated by trigonometry and geometry
a curious trig and geometry at that
entirely independent of the idiosyncrasies of radio antennas.
and unzipped software propagation forecasters too?

Hi Reggie,

I especially enjoy how you attempt to poison the restaurant to kill
waiter:
How does Eznec know
How does Eznec know
How does Eznec know
How does Eznec know
Eznec doesn't know
Which presumes a claim (four of them in fact) not made (except by you,
but then anyone can put antenna modeling tools to foolish propagation
uses).

I won't ask for substantiation on your geometry, Lord Kelvinator has
turned his back on these absurd proceedings too. I will leave you
with the last exasperated gasp.

73's
Richard Clark, KB7QHC

"Reg Edwards" wrote in message
...

"Yuri Blanarovich" wrote in message
...
Reg wrote:
The type of antenna or its radiation pattern has nothing whatever
to
do with the path taken by the radio wave through the ionosphere.
The
take-off angle and its name, generated by EZNEC, can be very
misleading.


It has to do. It allows us to direct the RF under desired angle to
hit the
layer or region that supports the propagation to the chosen target.
=========================================
Yuri,

The elevation angle of the radio path from the transmitter on its way
to the target changes with the number of hops.


The ionospheric propagation is not that clear cut simple, it is very
complicated. We have reflections going on and we have refractions going on
in the media that is like stormy sea. With the same height layer, and
uniform conditions, you can have more hops under higher launching angle, or
you can have fewer hops under lower angles. There could be another higher
layer with more complications of ducting or "bouncing" between the layers.

How does Eznec know the number of hops? How does Eznec know which
angle is correct? How does Eznec know the height of the reflecting
layers? How does Eznec know the distances at which the radio wave
returns to Earth to be re-reflected?

EZNEC knows sheeet about propagation. EZNEC and other antenna modeling
software can calculate the radiation pattern of modeled (not real) antenna
according to given ground parameters and antenna geometry. It gives you idea
how the pattern looks, but not the where the signal goes after entering
propagation media.

Eznec doesn't know. And neither does the radio operator unless he
estimates everything AFTER the event.


I know based on my experience operating at various times in the sunspot
cycle and my knowledge of propagation. There are now quite good propagation
programs that based on propagation indices and flux numbers, can give rough
idea where is the bulk of propagating going. Extreme antennas can do one
better, propagate where software doesn't think you can.

Radio waves follow paths dictated by trigonometry and geometry and are
entirely independent of the idiosyncrasies of radio antennas.
----
Reg.

Very fuzzy trig and geometry, it is not polished mirrors out there, it is
fuzzy bunch of ion-clouds like "hamburgers" that do their thing massaging
the signals. By using antennas that have stearable pattern, vertically and
horizontally one can take advantage of various modes of propagation. So it
takes natenna "idiot syncracies" to dictate where the signal goes, and how
it will propagate, conditions permitting.
See my article on "conducting" way back in CQ Magazine
http://members.aol.com/ve3bmv/bmvpropagation.htm

Yuri, K3BU, VE3BMV

On Wed, 17 May 2006 20:15:24 +0100, "Reg Edwards"
wrote:


How does Eznec know the number of hops? How does Eznec know which
angle is correct? How does Eznec know the height of the reflecting
layers? How does Eznec know the distances at which the radio wave
returns to Earth to be re-reflected?

Eznec doesn't know. And neither does the radio operator unless he
estimates everything AFTER the event.

Radio waves follow paths dictated by trigonometry and geometry and are
entirely independent of the idiosyncrasies of radio antennas.
----
Reg.


Reg, what were you drinking when you wrote this? EZNEC doesn't deal
at all with the atmosphere, it deals with the antenna. If the antenna
has a stronger lobe at 10 degrees in some given direction, EZNEC plots
it, but that doesn't mean the signal will come from that direction.

I have done only a little modeling with the ARRL version and the newer
free one. EZNEC plots the angles of the antenna from a horizontal and
vertical standpoint. Some antennas create single or double, primary
lobes, and others have more primary (highest gain) lobes. However,
when you change the elevation angle that you are watching, those
primary lobes may change to a different angle.

--
73 for now
Buck
N4PGW

Ken Bessler wrote:
Lets assume a single hop 40m signal from 400 miles away. What
elevation angle does it arrive at? Both stations are using inverted V's
at nominal height. There are no large bodies of water in between.

Daytime and/or nighttime.

That chart is in the ARRL Antenna Book. Assuming F2 layer
reflection, the arriving angle is reported to be in excess
of 50 degrees.
--
73, Cecil http://www.qsl.net/w5dxp

Cec, there you go again, quoting the bibles!

If the F2 is present then it must be daylight.

And if its daylight then the E-Layer must also be present.

For a groundpath distance of 400 miles the most likely reflector is
the E-Layer. In daylight the E-Layer is an excellent, stable
reflector. Furthermore, the radio path distance is considerably
shorter than via the higher F1 or F2-Layers.

The height of the E-Layer is about 70 miles.

Assuming a flat Earth, the elevation angle is -

ArcTan(70/200) = 19 degrees.

It depends to some extent on the E-Layer critical frequency and the
MUF. If the MUF is low enough and the transmit frequency is high
enough, e.g., 14 or 21 MHz, then the wave may pass right through the
E-Layer and be reflected most likely by the F1-Layer at a height of
roughly 300 miles.

Signals received via the F-Layers, if received at all, will be weaker
than via the E-Layer, if only because the path length is greater.

The elevation angle via the F1-Layer will be about -

ArcTan(300/200) = 56 degrees.

At night the E and F2 layers disappear. There remains only the
nighttime F at a height of about 200 miles to give an elevation angle
of 45 degrees.

That is, of course, if the nighttime-F critical frequency and MUF
allows propagation. There are such things as skip distances.

( Roy, no, I havn't made arrangements with high power broadcasters at
known distances to make tests to prove the foregoing predictions. And
yes, I know it's refraction and not reflection.)
----
Reg, G4FGQ.
========================================

"Cecil Moore" wrote in message
. net...
Ken Bessler wrote:
Lets assume a single hop 40m signal from 400 miles away. What
elevation angle does it arrive at? Both stations are using
inverted V's
at nominal height. There are no large bodies of water in between.

Daytime and/or nighttime.

That chart is in the ARRL Antenna Book. Assuming F2 layer
reflection, the arriving angle is reported to be in excess
of 50 degrees.
--
73, Cecil http://www.qsl.net/w5dxp

That is, of course, if the nighttime-F critical frequency and MUF
allows propagation. There are such things as skip distances.

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

Simplified Critical Frequencies, MUF and Skip Distances.

At a vertical elevation angle of 90 degrees, the Critical Frequency is
that frequency above which the radio wave passes right through the
layer and is not reflected.

It may be reflected back to Earth by a higher layer if there is one.
If the critical frequency of the higher layer is not high enough then
the wave may pass through that layer too and be lost forever.

Critical frequencies are generally at the lower HF frequencies and
depend on geographical latitude, the angle of the sun, time of day,
winter or summer, and on the state of the sun. That's why Near
Vertical Incidence transmissions are at low frequencies in the 80m and
sometimes in the 40m bands and are uncertain.

As the transmit elevation angle changes from vertical, the angle of
incidence of the wave with the ionospheric layer becomes less than 90
degrees and frequencies greater than critical begin to be reflected.

The Maximum Usable Frequency (MUF), that is the highest frequency
which is reflected, is aways higher than the critical frequency. It
is given by MUF = Fcrit/Sin(Phi) where Phi is the angle of incidence
of the wave with the layer. The MUF can be several times critical
frequency - conditions which occur at very low transmit elevation
angles.

This explains how best DX is obtained on the 15m and 10m amateur bands
at the height of the sun-spot cycle when critical frequencies are at
their maximum but still relatively low. Nobody points their 10m beams
up into the sky to work DX. Very low angle radiation is called for.
Yagi beam booms are horizontal, pointed at the horizon.

The lower the elevation angle of the radio path the higher is the MUF.
There is a skip distance. At distances less than the skip distance
nothing can be heard. This is because the operating frequency is too
high. It is greater than the MUF and the wave passes through the layer
without reflection. The lower the operating frequency the shorter is
the skip distance. Eventually, at MF, there is only Near Vertical
Incidence radiation and groundwave.

I trust the foregoing makes sense.

There is a short table of typical critical frequencies in the notes
attached to program SKYTRIG. They have been collected over the years
from various sources. MUF = Fcrit/Sin(Phi). To find Phi use the
program. It's only trigonometry.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

An equation that I leave in my HP calculator interrelates the important
parameters.

T = take-of-angle (up from horizon)
D = distance in Mm (40 Mm is all of the way around the earth)
H = virtual height of ionosphere in km

Calculator is using angles in degrees.
Single hop

Cos(T) / Cos(T + 4.5*D) = 1 + H/6366

F2 H for 40 degrees north is between about 250 and 370.

73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Ken Bessler" wrote in message
news:VEmag.22577$4H.10017@dukeread03...
Lets assume a single hop 40m signal from 400 miles away. What
elevation angle does it arrive at? Both stations are using inverted V's
at nominal height. There are no large bodies of water in between.

Daytime and/or nighttime.

--
73's de Ken KG0WX -