In message , FranK Turner-Smith G3VKI
writes
"Fred Roberts" wrote in message
...
On 28/11/2015 22:11, gareth wrote:
Spike recently commented upon his success with DX by implementing at
the base of his vertical antenna a fan of 300 ground wires pointing
in the direction that he wished to work.

I've not seen my suggestion before, but why could one not just have a
1/4 wave vertical, with the other 1/4 wave making up the dipole being
rotatable for the desired direction of working?

This was covered in, IIRC, Pat Hawkers Technical Topics many years
ago. The Americans had done some research on this very topic during
the Vietnam war, if one bends a vertical dipole so that the two
elements are at right angles to each other it is possible it would
seem to get some directivity in the direction of the horizontal element.


As I'm sure we both know, if a horizontal half wave dipole is turned so
the element runs east to west, the maximum radiation will be north and
south, with nulls to the east and west.
If the dipole is now turned vertically, the nulls would be upwards and
downwards and the horizontal radiation would be omni-directional.
I've not tried this, but my gut feeling is that if the elements were at
right angles you would get a combination of the two radiation patterns,
hence some degree of directivity in the form of a null in the direction
the horizontal element was pointing.

Isn't it the other way around?

Think what happens if you start with the radiation diagram of a straight
vertical dipole, and then consider what happens when you progressively
raise the lower leg. The once-straight halfwave dipole starts to form a
V, and in the direction of the legs of the V, the radiation will start
to become somewhat more concentrated. Away from the legs of the V, the
radiation starts to become more spread out. However, I don't think you
can go too far with this reasoning before you start to lose the slight
amount of benefit you obtained.
--
Ian

"Ian Jackson" wrote in message
...
In message , FranK Turner-Smith G3VKI
writes
"Fred Roberts" wrote in message
...
On 28/11/2015 22:11, gareth wrote:
Spike recently commented upon his success with DX by implementing at
the base of his vertical antenna a fan of 300 ground wires pointing
in the direction that he wished to work.

I've not seen my suggestion before, but why could one not just have a
1/4 wave vertical, with the other 1/4 wave making up the dipole being
rotatable for the desired direction of working?

This was covered in, IIRC, Pat Hawkers Technical Topics many years ago.
The Americans had done some research on this very topic during the
Vietnam war, if one bends a vertical dipole so that the two elements
are at right angles to each other it is possible it would seem to get
some directivity in the direction of the horizontal element.

As I'm sure we both know, if a horizontal half wave dipole is turned so
the element runs east to west, the maximum radiation will be north and
south, with nulls to the east and west.
If the dipole is now turned vertically, the nulls would be upwards and
downwards and the horizontal radiation would be omni-directional.
I've not tried this, but my gut feeling is that if the elements were at
right angles you would get a combination of the two radiation patterns,
hence some degree of directivity in the form of a null in the direction
the horizontal element was pointing.

Isn't it the other way around?

Think what happens if you start with the radiation diagram of a straight
vertical dipole, and then consider what happens when you progressively
raise the lower leg. The once-straight halfwave dipole starts to form a V,
and in the direction of the legs of the V, the radiation will start to
become somewhat more concentrated. Away from the legs of the V, the
radiation starts to become more spread out. However, I don't think you can
go too far with this reasoning before you start to lose the slight amount
of benefit you obtained.

Yeah, ****ed again, you're right. Thinking back to the days of band 1 TV
aerials (as they were known then), the dipole and reflector "H" array was
folded into an "X" which would have worked in the way you describe. Other
advantages were a reduction in weight and windage, plus a saving of
materials.
--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.uk

In rec.radio.amateur.antenna gareth wrote:
Spike recently commented upon his success with DX by implementing at
the base of his vertical antenna a fan
of 300 ground wires pointing in the direction that he wished to work.

I've not seen my suggestion before, but why could one not just have
a 1/4 wave vertical, with the other 1/4 wave making up the dipole
being rotatable for the desired direction of working?

Out of curiousity, I modeled the following:

freq: 14.2 MHz

radial height: 3 inches

Material: #12 copper

ground: average

I optimized the radiator and radial lengths for minimum reactance and got:

radiator: 196 inches

radial: 190.6 inches

R: 75 Ohms

X: -0.4 Ohms

SWR: 1.5

Maximum gain: -1.8 dBi in the direction of the radial and an elevation
angle of 30 degrees

Reverse gain: -6.8 dBi

Polarization: primarily vertical with horizontal lobes 90 degrees to the
radial a -15 dB down from the max vertical gain.


--
Jim Pennino

wrote in message ...

In rec.radio.amateur.antenna gareth wrote:
Spike recently commented upon his success with DX by implementing at
the base of his vertical antenna a fan
of 300 ground wires pointing in the direction that he wished to work.

I've not seen my suggestion before, but why could one not just have
a 1/4 wave vertical, with the other 1/4 wave making up the dipole
being rotatable for the desired direction of working?

Out of curiousity, I modeled the following:

freq: 14.2 MHz

radial height: 3 inches

Material: #12 copper

ground: average

I optimized the radiator and radial lengths for minimum reactance and got:

radiator: 196 inches

radial: 190.6 inches

R: 75 Ohms

X: -0.4 Ohms

SWR: 1.5

Maximum gain: -1.8 dBi in the direction of the radial and an elevation
angle of 30 degrees

Reverse gain: -6.8 dBi

Polarization: primarily vertical with horizontal lobes 90 degrees to the
radial a -15 dB down from the max vertical gain.

Cool. Any idea what the numbers would be for the 300 radial configuration?

In rec.radio.amateur.antenna Wayne wrote:


wrote in message ...

In rec.radio.amateur.antenna gareth wrote:
Spike recently commented upon his success with DX by implementing at
the base of his vertical antenna a fan
of 300 ground wires pointing in the direction that he wished to work.

I've not seen my suggestion before, but why could one not just have
a 1/4 wave vertical, with the other 1/4 wave making up the dipole
being rotatable for the desired direction of working?

Out of curiousity, I modeled the following:

freq: 14.2 MHz

radial height: 3 inches

Material: #12 copper

ground: average

I optimized the radiator and radial lengths for minimum reactance and got:

radiator: 196 inches

radial: 190.6 inches

R: 75 Ohms

X: -0.4 Ohms

SWR: 1.5

Maximum gain: -1.8 dBi in the direction of the radial and an elevation
angle of 30 degrees

Reverse gain: -6.8 dBi

Polarization: primarily vertical with horizontal lobes 90 degrees to the
radial a -15 dB down from the max vertical gain.

Cool. Any idea what the numbers would be for the 300 radial configuration?

Likely not a lot of difference.

I could add a few, but not going to spend the time to add 300.

--
Jim Pennino

In rec.radio.amateur.antenna wrote:
In rec.radio.amateur.antenna Wayne wrote:


wrote in message ...

In rec.radio.amateur.antenna gareth wrote:
Spike recently commented upon his success with DX by implementing at
the base of his vertical antenna a fan
of 300 ground wires pointing in the direction that he wished to work.

I've not seen my suggestion before, but why could one not just have
a 1/4 wave vertical, with the other 1/4 wave making up the dipole
being rotatable for the desired direction of working?

Out of curiousity, I modeled the following:

freq: 14.2 MHz

radial height: 3 inches

Material: #12 copper

ground: average

I optimized the radiator and radial lengths for minimum reactance and got:

radiator: 196 inches

radial: 190.6 inches

R: 75 Ohms

X: -0.4 Ohms

SWR: 1.5

Maximum gain: -1.8 dBi in the direction of the radial and an elevation
angle of 30 degrees

Reverse gain: -6.8 dBi

Polarization: primarily vertical with horizontal lobes 90 degrees to the
radial a -15 dB down from the max vertical gain.

Cool. Any idea what the numbers would be for the 300 radial configuration?

Likely not a lot of difference.

I could add a few, but not going to spend the time to add 300.


OK, I added radials for a total of 5 in a 45 degree spread and optimized
for minimum reactance.

radiator: 203 inches

radial: 186 inches

R: 52.4 Ohms

X: 0.4 Ohms

SWR: 1.1

Maximum gain: -.18 dBi in the direction of the radial and an elevation
angle of 30 degrees

Reverse gain: -3.7 dBi

Note with one radial the F/B ratio is about 5 dB and with five radials
it is about 3dB.

About the only thing I can see worth noting about this antenna is that
it shows more radials are better, but everyone already knows that.


--
Jim Pennino

wrote in message ...

In rec.radio.amateur.antenna wrote:
In rec.radio.amateur.antenna Wayne wrote:


wrote in message ...

In rec.radio.amateur.antenna gareth wrote:
Spike recently commented upon his success with DX by implementing at
the base of his vertical antenna a fan
of 300 ground wires pointing in the direction that he wished to work.

I've not seen my suggestion before, but why could one not just have
a 1/4 wave vertical, with the other 1/4 wave making up the dipole
being rotatable for the desired direction of working?

Out of curiousity, I modeled the following:

freq: 14.2 MHz

radial height: 3 inches

Material: #12 copper

ground: average

I optimized the radiator and radial lengths for minimum reactance and
got:

radiator: 196 inches

radial: 190.6 inches

R: 75 Ohms

X: -0.4 Ohms

SWR: 1.5

Maximum gain: -1.8 dBi in the direction of the radial and an elevation
angle of 30 degrees

Reverse gain: -6.8 dBi

Polarization: primarily vertical with horizontal lobes 90 degrees to the
radial a -15 dB down from the max vertical gain.

Cool. Any idea what the numbers would be for the 300 radial
configuration?

Likely not a lot of difference.

I could add a few, but not going to spend the time to add 300.


# OK, I added radials for a total of 5 in a 45 degree spread and optimized
# for minimum reactance.

# radiator: 203 inches

# radial: 186 inches

# R: 52.4 Ohms

# X: 0.4 Ohms

# SWR: 1.1

# Maximum gain: -.18 dBi in the direction of the radial and an elevation
# angle of 30 degrees

# Reverse gain: -3.7 dBi

# Note with one radial the F/B ratio is about 5 dB and with five radials
# it is about 3dB.

# About the only thing I can see worth noting about this antenna is that
# it shows more radials are better, but everyone already knows that.

Interesting. Doesn't seem like it would be worth the effort to add radials
in this case.

On 29/11/2015 23:24, wrote:

OK, I added radials for a total of 5 in a 45 degree spread and optimized
for minimum reactance.

radiator: 203 inches, radial: 186 inches, R: 52.4 Ohms, X: 0.4 Ohms

SWR: 1.1, Maximum gain: -.18 dBi in the direction of the radial and an elevation
angle of 30 degrees, Reverse gain: -3.7 dBi

Note with one radial the F/B ratio is about 5 dB and with five radials
it is about 3dB.

About the only thing I can see worth noting about this antenna is that
it shows more radials are better, but everyone already knows that.

Imagine a case whereby someone digs up the soil around the base of a
vertical antenna, a couple of feet deep and as far out as the antenna is
tall. Into this they mix 2 percent of high-aspect-ratio thin conducting
fibres, say about a foot long, and then replace the soil. 2 percent of
conducting fibres in an essentially non-conducting medium is about the
minimum proportion necessary to reach the percolation threshold..

What results from your modelling exercise do you get in this case?


--
Spike

"Crime butchers innocence to secure a throne, and innocence struggles
with all its might against the attempts of crime"

- Maximilien Robespierre