Al Lorona wrote:
"How does one determine the correct antenna takeoff angle to communicate
over a certain sistance?"

Solve the trigonometry / geometry problem involving the target distance
and height of the reflecting layer.

King, Mimno and Wing in "Transmission Lines, Antennas, and Wave
Guides"say:
Elevation angles above 3-degrees are useful because they are not
immediately absorbed by earth loss. Low-angle radiation (above
3-degrees) makes a long distance trip to a distant receiver with the
fewest hops or bounces between the ionosphere and earth. At 3-degree
elevation, the distance per hop is about 3.500 km (2.100 miles). longer
distances are automatically broken up into units not exceeding 3.500 km.
Multipath transmission often exists and causes fading.

For distances less than 3,500 km, elevation angles of more than
3-degrees must be used. Often the antenna radiates a broad vertical
pattern. In any case, the useful ray becomes steeper as the receiver
becomes closer to the transmitter.

Kraus in edition No. 3 of "Antennas" shows how earth reflection affects
the pattern and impedance of a horizontal antenna. At 1/2-wavelength
elevation, the antenna has maximum radiation at 30-degrees over perfect
earth and the center-fed 1/2-wave horizontal dipole has a feedpoint of
73 ohms. The Zepp should have about the same vertical maximum radiation
angle but its impedance is something else.

Elevation angle is an inverse function of antenna height.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote in message
...

King, Mimno and Wing in "Transmission Lines, Antennas, and Wave
Guides"say:
Elevation angles above 3-degrees are useful because they are not
immediately absorbed by earth loss. Low-angle radiation (above
3-degrees) makes a long distance trip to a distant receiver with the
fewest hops or bounces between the ionosphere and earth. At 3-degree
elevation, the distance per hop is about 3.500 km (2.100 miles). longer
distances are automatically broken up into units not exceeding 3.500 km.
Multipath transmission often exists and causes fading.

For distances less than 3,500 km, elevation angles of more than
3-degrees must be used. Often the antenna radiates a broad vertical
pattern. In any case, the useful ray becomes steeper as the receiver
becomes closer to the transmitter.

Kraus in edition No. 3 of "Antennas" shows how earth reflection affects
the pattern and impedance of a horizontal antenna. At 1/2-wavelength
elevation, the antenna has maximum radiation at 30-degrees over perfect
earth and the center-fed 1/2-wave horizontal dipole has a feedpoint of
73 ohms. The Zepp should have about the same vertical maximum radiation
angle but its impedance is something else.

Elevation angle is an inverse function of antenna height.

Best regards, Richard Harrison, KB5WZI


Hi, Richard,

Yeah, your reference sounds about right. On Roy's suggestion, I downloaded
W6ELprop and was shocked to find what the elevation angles are for even
moderate path lengths. For example, I ran the path from Albuquerque to
Philadelphia and was amazed to find that the signal would have to leave the
antenna and reflect from the F layer at a 4 degree angle!! That's darn near
parallel to the reflecting surface! This is far, far lower than I had ever
thought. Most antennas have radiation at this angle, of course, but it is
usually way down from the main lobe.

Even for double-hop contacts, I believe that the angle was something like 8
or 10 degrees for that same path, but I don't remember exactly right now.

You cite that a 1/2-wave-high horizontal antenna has a maximum lobe at 30
degrees. Starting at Albuquerque, that 30 degrees will get you only to about
Oklahoma City on the first hop. Again, this surprised me. Believe me, I am
becoming disabused of my previous erroneous notions.

These numbers are all for 40 meters and below. If the horizontal antenna in
question is operated on a higher frequency, there's no guarantee (if I am
reading the data in W6ELprop correctly) that a 30 degree incident angle will
be reflected at all.

I tend to grow jaded upon hearing east coast stations (I am in Los Angeles)
on 40, but now I will appreciate the physics necessary to make such a thing
possible.

I am also going to have to put up my Field Day antenna much, much higher
than previously thought.

Regards,

Al W6LX

As an alternative to putting your Field Day antenna higher, consider
finding a location that will enhance lower angle radiation. 10 dB
improvement over flat ground isn't too hard to come by in hilly or
mountainous terrain. The best program I've seen for determining this is
TA (Terrain Analysis), a DOS program which I believe you can still get
from its author, Brian Beezley, K6STI. Last I heard, he'll only take
orders by mail.

I have the same general problem here in Oregon, perhaps even more so. My
Field Day antennas and location are chosen as though I were after DX.
You might be interested in the "Field Day Special", an antenna I've used
for many years from here -- it might also be suitable for you. You can
find the info at http://www.eznec.com/Amateur/Articles/.

Roy Lewallen, W7EL

Al Lorona wrote:

Hi, Richard,

Yeah, your reference sounds about right. On Roy's suggestion, I downloaded
W6ELprop and was shocked to find what the elevation angles are for even
moderate path lengths. For example, I ran the path from Albuquerque to
Philadelphia and was amazed to find that the signal would have to leave the
antenna and reflect from the F layer at a 4 degree angle!! That's darn near
parallel to the reflecting surface! This is far, far lower than I had ever
thought. Most antennas have radiation at this angle, of course, but it is
usually way down from the main lobe.

Even for double-hop contacts, I believe that the angle was something like 8
or 10 degrees for that same path, but I don't remember exactly right now.

You cite that a 1/2-wave-high horizontal antenna has a maximum lobe at 30
degrees. Starting at Albuquerque, that 30 degrees will get you only to about
Oklahoma City on the first hop. Again, this surprised me. Believe me, I am
becoming disabused of my previous erroneous notions.

These numbers are all for 40 meters and below. If the horizontal antenna in
question is operated on a higher frequency, there's no guarantee (if I am
reading the data in W6ELprop correctly) that a 30 degree incident angle will
be reflected at all.

I tend to grow jaded upon hearing east coast stations (I am in Los Angeles)
on 40, but now I will appreciate the physics necessary to make such a thing
possible.

I am also going to have to put up my Field Day antenna much, much higher
than previously thought.

Regards,

Al W6LX