Queston on Yagi Antennae
 

Andy writes;

I know I could go to my EZNEC and find this out for myself,
but I figure someone here has already done this and a quick
answer is all I need..

In "normal" Yagi antennae, the elements are parallel
and at 90 degrees to the mounting boom.

In some TV antennae, the elements are at an angle to the
mounting boom, slanted in the direction of the station being
received. Otherwise, they look pretty much like a Yagi.

My question is, what effect does "slanting" the elements
forward have on the impedance, and the pattern ?

[ [ [ [ [ [

Normal Yagi Slanted Yagi


Thanks in advance for the meaningful answers..

Andy W4OAH

Queston on Yagi Antennae
 

"AndyS" wrote in message
oups.com...
Andy writes;

I know I could go to my EZNEC and find this out for myself,
but I figure someone here has already done this and a quick
answer is all I need..

In "normal" Yagi antennae, the elements are parallel
and at 90 degrees to the mounting boom.

In some TV antennae, the elements are at an angle to the
mounting boom, slanted in the direction of the station being
received. Otherwise, they look pretty much like a Yagi.

My question is, what effect does "slanting" the elements
forward have on the impedance, and the pattern ?

[ [ [ [ [ [

Normal Yagi Slanted Yagi


Thanks in advance for the meaningful answers..

Andy W4OAH

Hi Andy

The TV antennas with the V shaped elements arent Yagi antennas. Log
periodic V antennas are fed from their "front end" to produce a minimum
toward the rear.
A TV Yagi antenna is good for any one channel. A LPV antenna is good
for all the channels but not as good for the one channel the yagi tunes to.
The LPV elements are slanted to an angle where their radiation pattern
adds in the Forward direction when they are a 3/2 WL dipole.


Jerry

Queston on Yagi Antennae
 

AndyS wrote:
Andy writes;

I know I could go to my EZNEC and find this out for myself,
but I figure someone here has already done this and a quick
answer is all I need..

In "normal" Yagi antennae, the elements are parallel
and at 90 degrees to the mounting boom.

In some TV antennae, the elements are at an angle to the
mounting boom, slanted in the direction of the station being
received. Otherwise, they look pretty much like a Yagi.

My question is, what effect does "slanting" the elements
forward have on the impedance, and the pattern ?

[ [ [ [ [ [

Normal Yagi Slanted Yagi


Thanks in advance for the meaningful answers..

Andy W4OAH


Normally elements like that would not be used, but if you want to make a
yagi that runs at 1f and 3f, "slanting" the elements allows it to have a
reasonable pattern on triple the normal frequency while not mucking up
how it runs at the 1f too badly. 144 and 432 work fairly well.

If you turn the trick right, the metal in question will work on 6, 2 and 70.

tom
K0TAR


tom
K0TAR

Queston on Yagi Antennae
 

On 12 Feb, 05:02, "AndyS" wrote:
Andy writes;

I know I could go to my EZNEC and find this out for myself,
but I figure someone here has already done this and a quick
answer is all I need..

In "normal" Yagi antennae, the elements are parallel
and at 90 degrees to the mounting boom.

In some TV antennae, the elements are at an angle to the
mounting boom, slanted in the direction of the station being
received. Otherwise, they look pretty much like a Yagi.

My question is, what effect does "slanting" the elements
forward have on the impedance, and the pattern ?

[ [ [ [ [ [

Normal Yagi Slanted Yagi

Thanks in advance for the meaningful answers..

Andy W4OAH

Very true, a yagi is a planar antenna i.e on a single plane whereas
only one element is resonant and where ALL others are parasitic. This
also holds true for a log periodic except the frequency is a variable
which selects the element closest to resonance for the theoretical
feed point i.e. of matching impedance to the feed point impedance. The
point about just one element that is resonant is the reason in my mind
that antenna advancement
has been retarded over the last hundred years excabated by the design
of the yagi which is really an empirical design that denies the
simplicity of normal radiation and its corresponding mathematics. Now
I know somebody will immediately jump to the dual driven element forms
but that is beside the point under discussion.
Art

Queston on Yagi Antennae
 

On 12 Feb, 05:02, "AndyS" wrote:
Andy writes;

I know I could go to my EZNEC and find this out for myself,
but I figure someone here has already done this and a quick
answer is all I need..

In "normal" Yagi antennae, the elements are parallel
and at 90 degrees to the mounting boom.

In some TV antennae, the elements are at an angle to the
mounting boom, slanted in the direction of the station being
received. Otherwise, they look pretty much like a Yagi.

My question is, what effect does "slanting" the elements
forward have on the impedance, and the pattern ?

[ [ [ [ [ [

Normal Yagi Slanted Yagi

Thanks in advance for the meaningful answers..

Andy W4OAH

Quick answer you say ? A change in direction of current flow inpedes
that flow. Radiation is at right angles to the radiator thus radiation
drops of at the centre at that same point.
Short enough ?
Art

Queston on Yagi Antennae
 

Here's why some of the TV antenna elements are V shaped, and you can
verify this with your EZNEC in a couple of minutes:

Take a 40 meter dipole and excite it on 15 meters. You'll find you get a
cloverleaf pattern. Now bend each of the arms 30 degrees to form a vee
with 120 degree included angle. You'll see that the lobes in the
cloverleaf now line up to make a bidirectional pattern. The pattern on
40 meters isn't changed much by this modification. So you can make an
effective 40/15 meter bidirectional antenna using this technique. (I've
done it. Works great -- as long as the stations you want to talk to are
in line with the lobes.)

The upper TV channels are approximately three times the frequency of the
lower ones, just like 40 and 15 meters. So the same trick is used for TV
antennas, making some elements do double duty.

This is, by the way, the principle behind the vee beam. As you make the
dipole longer and longer, the lobes point more and more away from the
center and toward the end. So you have to bend the antenna at more and
more of an angle to get them to line up. This is where the graph showing
optimum angle vs vee beam leg length comes from.

Roy Lewallen, W7EL

AndyS wrote:
Andy writes;

I know I could go to my EZNEC and find this out for myself,
but I figure someone here has already done this and a quick
answer is all I need..

In "normal" Yagi antennae, the elements are parallel
and at 90 degrees to the mounting boom.

In some TV antennae, the elements are at an angle to the
mounting boom, slanted in the direction of the station being
received. Otherwise, they look pretty much like a Yagi.

My question is, what effect does "slanting" the elements
forward have on the impedance, and the pattern ?

[ [ [ [ [ [

Normal Yagi Slanted Yagi


Thanks in advance for the meaningful answers..

Andy W4OAH