Assume there is only one spot on your hilly land that you can pull in
your favorite FM station, 90 Mhz, over the competition, and only with
a horizontal dipole at a certain azimuth. A Yagi doesn't help, as
we are depending fully on the null.

Assuming we are stuck with this position, how can we enhance our
dipole? I am the owner of great sheets of metal. Can I put my great
sheets of metal to use in e.g. a dipole made of two great sheets of
metal?

Assume there is only one spot on your hilly land that you can pull in
your favorite FM station, 90 Mhz, over the competition, and only with
a horizontal dipole at a certain azimuth. A Yagi doesn't help, as
we are depending fully on the null.

Commercial FM stations are vertically polarized, cause most of the people
that listen are in cars. I have found this to be true in my homebrew antennas
(at least around here). You might try changing the polarization, and see if
that helps.

Not sure why you think a yagi won't help. A 3 or 4 el. yagi with a good F/B
and proper polarization will be a big improvement over the end nulls of a
dipole.

Using great sheets of metal for a dipole will increase the bandwidth, but
that is not what you are looking for. Using the great sheets of metal for a
screen reflector, or corner reflector could produce some big improvements.

73 Gary N4AST

"JGBOYLES" wrote in message
...
Assume there is only one spot on your hilly land that you can pull in
your favorite FM station, 90 Mhz, over the competition, and only with
a horizontal dipole at a certain azimuth. A Yagi doesn't help, as
we are depending fully on the null.

Commercial FM stations are vertically polarized, cause most of the
people
that listen are in cars.


I thought the FCC required equal EIRP of both vertical AND horizontal
polarization for an FM broadcast station? Did the horizontal requirement get
deleted?

Ed
wb6wsn

I thought the FCC required equal EIRP of both vertical AND horizontal
polarization for an FM broadcast station? Did the horizontal requirement get
deleted?

I don't know, just reporting on the results of my tinkering, I get by far the
best signal with vertical polarization. I assumed that was becuse they wanted
to target automobiles. Maybe the EIPR of the stations in both the vertical
and horizontal planes in my area are not in compliance?
73 Gary N4AST

You could make a slot antenna? ie cut a rectangle out of the metal sheet
(say) 2" wide and a little over 1/2 wave at the op freq. From memory
you'll get pretty close to 50/75r and the polaraisation is 90deg to the
slot.

Doubt it helps but worth a mention..

Cheers Bob VK2YQA

Dan Jacobson wrote:
Assume there is only one spot on your hilly land that you can pull in
your favorite FM station, 90 Mhz, over the competition, and only with
a horizontal dipole at a certain azimuth. A Yagi doesn't help, as
we are depending fully on the null.

Assuming we are stuck with this position, how can we enhance our
dipole? I am the owner of great sheets of metal. Can I put my great
sheets of metal to use in e.g. a dipole made of two great sheets of
metal?

Most of the FM stations broadcast circular polarization, but it seems
that more of the hoz part gets attenuated by trees more than vertical.
So if there is a shallow angle to the transmitter, through some vegetation
Vert seems more dominant.

But I think this changes with over-the-horizon, and it gets more Hoz,
but I have not measured this.

On the original question, you can add antenna patterns if they are phased
right.
You can put a piece of metal in the direct path to block signal, may go down
10 dB or so.
Metal could be screen wire mesh between dipole and unwanted transmitter 10
by 10,
centered to get phase null in the back.



"JGBOYLES" wrote in message
...
I thought the FCC required equal EIRP of both vertical AND horizontal
polarization for an FM broadcast station? Did the horizontal requirement
get
deleted?

I don't know, just reporting on the results of my tinkering, I get by far
the
best signal with vertical polarization. I assumed that was becuse they
wanted
to target automobiles. Maybe the EIPR of the stations in both the
vertical
and horizontal planes in my area are not in compliance?
73 Gary N4AST

Dan Jacobson wrote:
Assume there is only one spot on your hilly land that you can pull in
your favorite FM station, 90 Mhz, over the competition, and only with
a horizontal dipole at a certain azimuth. A Yagi doesn't help, as
we are depending fully on the null.

Assuming we are stuck with this position, how can we enhance our
dipole? I am the owner of great sheets of metal. Can I put my great
sheets of metal to use in e.g. a dipole made of two great sheets of
metal?

Nonsense; a properly constructed yagi will perform far better at rejecting
the undesired signal and maximizing the desired one than any dipole.

--
Jim Pennino

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In article ,
wrote:

Dan Jacobson wrote:
Assume there is only one spot on your hilly land that you can pull in
your favorite FM station, 90 Mhz, over the competition, and only with
a horizontal dipole at a certain azimuth. A Yagi doesn't help, as
we are depending fully on the null.

Assuming we are stuck with this position, how can we enhance our
dipole? I am the owner of great sheets of metal. Can I put my great
sheets of metal to use in e.g. a dipole made of two great sheets of
metal?

Nonsense; a properly constructed yagi will perform far better at rejecting
the undesired signal and maximizing the desired one than any dipole.

I get the impression that this whole discussion about reception
difficulties for 90 MHz FM signals is hypothetical, rather than an
attempt to solve an existing real problem.

Are you sure about the Yagi being better than a dipole under the
circumstances described? He said to assume that he is on hilly land. The
predicted performance of a Yagi is far-field performance. If the
surrounding terrain is bumpy enough close enough, perhaps the
performance might be rather different. If the field near the director is
substantially different from that near the driven element, and the field
near the reflector is different from both of those, perhaps a Yagi might
do a poorer job of discriminating against unwanted signals than a
smaller, simple, dipole would do, since the field in the neighborhood of
the smaller dipole would be more uniform. I'm not asserting that this
would be have to be the case, but it seems reasonable to me that it
might be the case.

Consider, for example, how FM broadcast signal strength and cleanliness
can vary markedly as one slowly moves one's car just a few inches, e.g.
in heavy traffic. This can happen both in downtown skyscraper jungles
and in the more natural mountainous terrain near where I live (Greater
Vancouver, BC, area), though in the mountains the heavy traffic is
blessedly absent. Clearly far-field assumptions are unwarranted under
such circumstances.

David, ex-W8EZE

--
David Ryeburn

To send e-mail, use "ca" instead of "caz".

David Ryeburn wrote:

I get the impression that this whole discussion about reception
difficulties for 90 MHz FM signals is hypothetical, rather than an
attempt to solve an existing real problem.

Are you sure about the Yagi being better than a dipole under the
circumstances described? He said to assume that he is on hilly land. The
predicted performance of a Yagi is far-field performance. If the
surrounding terrain is bumpy enough close enough, perhaps the
performance might be rather different. If the field near the director is
substantially different from that near the driven element, and the field
near the reflector is different from both of those, perhaps a Yagi might
do a poorer job of discriminating against unwanted signals than a
smaller, simple, dipole would do, since the field in the neighborhood of
the smaller dipole would be more uniform. I'm not asserting that this
would be have to be the case, but it seems reasonable to me that it
might be the case.

Entirely unreasonable for the following reasons:

The spacing between elements of a 90 MHz yagi is about 2 to 3 feet. It is
hard to imagine a 3 foot wide hill.

In other words, it would take some rather bizarre terrain to have a
different effect on the driven element than the director.

Further, the far field at 90 MHz is about 10 feet or so; one would
hope the antenna is at least 10 feet off the ground and the next
hill is more than 10 feet away.

With a dipole, you are depending on the null to minimize the undesired
signal and have little gain in the direction of the desired signal.

With a yagi, you still have the null (assuming a proper yagi) plus
additional gain in the desired direction. The net result is the ratio of
the signal strengths of the desired to undesired signals becomes greater.

Consider, for example, how FM broadcast signal strength and cleanliness
can vary markedly as one slowly moves one's car just a few inches, e.g.
in heavy traffic. This can happen both in downtown skyscraper jungles
and in the more natural mountainous terrain near where I live (Greater
Vancouver, BC, area), though in the mountains the heavy traffic is
blessedly absent. Clearly far-field assumptions are unwarranted under
such circumstances.

Clearly, far field assumptions ARE warrented under such circumstances.

What you are seeing is multiple reflections (in the far field) off the
various structures.

Yet another reason to get the antenna high; i.e. above the influence
of such structures.

David, ex-W8EZE


--
Jim Pennino

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Dan Jacobson wrote:
Assume there is only one spot on your hilly land that you can pull in
your favorite FM station, 90 Mhz, over the competition, and only with
a horizontal dipole at a certain azimuth. A Yagi doesn't help, as
we are depending fully on the null.

Assuming we are stuck with this position, how can we enhance our
dipole? I am the owner of great sheets of metal. Can I put my great
sheets of metal to use in e.g. a dipole made of two great sheets of
metal?

I should have probably also mentioned that making a dipole from
sheet elements mostly effects the bandwidth and has very little
effect on either the gain or the pattern.

Search the web for bat wing antenna for more info.

--
Jim Pennino

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