On 11 abr, 06:14, "J. Mc Laughlin" wrote:
Dear Wim PA3DJS:

How I wish that I could read Dutch. However, in looking over all of
your work, it continually occurred to me that much of the base of English
comes from Northern Nederland.

I looked at the first table on page 20 of your work. The information so
intrigued me that I ran almost the same information through NEC4, which does
well with antennas close to the ground. I assumed: a center frequency of
3.6 MHz, a horizontal half wave dipole slightly adjusted to be resonant at
3.6 MHz at each height, the use of Cu wire 2 mm in diameter, and earth with
a sigma of 0.01 and a relative dielectric constant of 15. This is what I
found without too obsessive an amount of tweaking:

The data is in this order:
height of the dipole in meters
the real part of the dipole's impedance in ohms
(the phase angle of the impedance was kept under 2 degrees)
the approximate SWR=2 BW in a 50 ohm system in kHz
the total apparent loss of the system in dB
(this is found by integrating gain in all directions)
the peak antenna gain in dBi

4.2 38.1 125 6.25 2.0
5.8 37.7 120 4.31 4.1
8.3 42.1 130 2.59 5.8
10.4 49.0 140 1.81 6.5
15 66.5 145 1.04 6.9
20.8 85.7 125 0.7 6.5

Most of my results are close to your results. It is interesting to know if
I used the same assumptions. Please let me know.

I encourage you to consider translating your work, or at least parts of it,
into English.

73, Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
Home:
[rest removed]

Dear Mac,

Thank you for sharing your results with me. You are fully right, the
results are almost the same. The difference with my assumptions is
wire diameter only. I used 10mm. I expected more difference in useful
bandwidth, because of the factor 5 in wire diameter.

The simulations were carried out on IE3D with a lossy dielectric as
ground. The first table on page 17, shows the results for a perfect
ground.

I wasn't satisfied with the bandwidth, so the actual antenna consists
of 2 wires (1m separation). This gave me sufficient bandwidth to use
the antenna without a tuner.

The results between the brackets are with 3 floating reflector wires
under the antenna (about 1 m above ground). This gives an evident
increase in gain. The gain increases somewhat by raising the 3 wires
to about 1.5..2m above ground.

At this moment there are no plans to translate the document into
English language. As you have seen, the text in the images is in
English language, so you never know what happens during a vacation.....
The birdth of the Dutch version was in Spain.

Best Regards,

Wim
PA3DJS.

"Wimpie" wrote in message
ups.com...
On 12 abr, 00:47, "Yuri Blanarovich" wrote:
"Wimpie" wrote in message

ps.com...





So if you suspended another dipole above your NVIS dipole and oriented
90
degrees to each other, the difference would be insignificant?
Then move it up into the "clouds", then move down to earth at the
distance
and you will see "insignificant" difference in signal levels?

Seems that direction finders should not work according to this
"verdict",
Eh?

One thing is the direction of the signals (maximum) another one is the
polarization. Based on the orientation of antennas, one can orient the
antenna to find the minimum signal.

Yuri, K3BU.us

Hi Yuri,

As the wave pass through the ionosphere, strange things happen. You
could google on Faraday rotation, ordinary and extraordinary waves to
find out that at low frequency, the change in polarization is
significant.

Change does not mean that polarization dissapears.

Based on the down coming wave, you cannot determine the orientation of
the transmitting antenna, neither the position with reasonable
accuracy (for NVIS propagation).

When you place the receiving antenna just above the transmitting
antenna you are right, but we were discussing NVIS propagation.

Best Regards,

Wim
PA3DJS

So when signal is reflected, the polarization disappears?

No, mostly the down comming wave has a circular component (eliptical
polarization), therefore the orientation is not of significant
importance. Wim, PA3DJS.

73 Yuri, K3BU


So if there is ANY polarization left how can you claim that is not of
significant importance.
The proof in the pudding is that on any signal one can with any antenna,
especially directional, find the spot where signal is minimal or nulled out.
Nulls are sharp vs. broad pattern, but one has to be aware of them and
understand the difference between the pattern and polarization.

Yuri, K3BU.us

Dear Wim:

Thank you for the additional information. The information fills in the
rest of the story.

Before I shut down the dedicated computer used for the calculations, I
looked at the last entry again. The 20.8 m high dipole in a 50 ohm system
seemed to have significantly smaller BW than what you reported. I changed
the impedance to 85.7 ohms and then found (using the same data) that the
SWR=2 BW is about 250 kHz. With a 1.3:1 turns ratio transformer, this is
also the expected BW that would be seen in a 50 ohm system.

In short, my reported BW numbers may need qualification. It is
interesting to see how two different simulation techniques reach similar
conclusions. I too expect that increasing the wire to 10 mm has little
effect.

Vacations can be very creative times. Thank you for your work. 73,
Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Wimpie" wrote in message
oups.com...
On 11 abr, 06:14, "J. Mc Laughlin" wrote:
Dear Wim PA3DJS:

How I wish that I could read Dutch. However, in looking over all of
your work, it continually occurred to me that much of the base of
English
comes from Northern Nederland.

I looked at the first table on page 20 of your work. The
information so
intrigued me that I ran almost the same information through NEC4, which
does
well with antennas close to the ground. I assumed: a center frequency
of
3.6 MHz, a horizontal half wave dipole slightly adjusted to be resonant
at
3.6 MHz at each height, the use of Cu wire 2 mm in diameter, and earth
with
a sigma of 0.01 and a relative dielectric constant of 15. This is what
I
found without too obsessive an amount of tweaking:

The data is in this order:
height of the dipole in meters
the real part of the dipole's impedance in ohms
(the phase angle of the impedance was kept under 2 degrees)
the approximate SWR=2 BW in a 50 ohm system in kHz
the total apparent loss of the system in dB
(this is found by integrating gain in all directions)
the peak antenna gain in dBi

4.2 38.1 125 6.25 2.0
5.8 37.7 120 4.31 4.1
8.3 42.1 130 2.59 5.8
10.4 49.0 140 1.81 6.5
15 66.5 145 1.04 6.9
20.8 85.7 125 0.7 6.5

Most of my results are close to your results. It is interesting to know
if
I used the same assumptions. Please let me know.

I encourage you to consider translating your work, or at least parts of
it,
into English.

73, Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
Home:
[rest removed]

Dear Mac,

Thank you for sharing your results with me. You are fully right, the
results are almost the same. The difference with my assumptions is
wire diameter only. I used 10mm. I expected more difference in useful
bandwidth, because of the factor 5 in wire diameter.

The simulations were carried out on IE3D with a lossy dielectric as
ground. The first table on page 17, shows the results for a perfect
ground.

I wasn't satisfied with the bandwidth, so the actual antenna consists
of 2 wires (1m separation). This gave me sufficient bandwidth to use
the antenna without a tuner.

The results between the brackets are with 3 floating reflector wires
under the antenna (about 1 m above ground). This gives an evident
increase in gain. The gain increases somewhat by raising the 3 wires
to about 1.5..2m above ground.

At this moment there are no plans to translate the document into
English language. As you have seen, the text in the images is in
English language, so you never know what happens during a vacation.....
The birdth of the Dutch version was in Spain.

Best Regards,

Wim
PA3DJS.

On 12 abr, 23:40, "Yuri Blanarovich" wrote:
"Wimpie" wrote in message

ups.com...

On 12 abr, 00:47, "Yuri Blanarovich" wrote:
"Wimpie" wrote in message

oups.com...

So if you suspended another dipole above your NVIS dipole and oriented
90
degrees to each other, the difference would be insignificant?
Then move it up into the "clouds", then move down to earth at the
distance
and you will see "insignificant" difference in signal levels?

Seems that direction finders should not work according to this
"verdict",
Eh?

One thing is the direction of the signals (maximum) another one is the
polarization. Based on the orientation of antennas, one can orient the
antenna to find the minimum signal.

Yuri, K3BU.us

Hi Yuri,

As the wave pass through the ionosphere, strange things happen. You
could google on Faraday rotation, ordinary and extraordinary waves to
find out that at low frequency, the change in polarization is
significant.

Change does not mean that polarization dissapears.

Based on the down coming wave, you cannot determine the orientation of
the transmitting antenna, neither the position with reasonable
accuracy (for NVIS propagation).

When you place the receiving antenna just above the transmitting
antenna you are right, but we were discussing NVIS propagation.

Best Regards,

Wim
PA3DJS

So when signal is reflected, the polarization disappears?

No, mostly the down comming wave has a circular component (eliptical
polarization), therefore the orientation is not of significant
importance. Wim, PA3DJS.

73 Yuri, K3BU

So if there is ANY polarization left how can you claim that is not of
significant importance.
The proof in the pudding is that on any signal one can with any antenna,
especially directional, find the spot where signal is minimal or nulled out.
Nulls are sharp vs. broad pattern, but one has to be aware of them and
understand the difference between the pattern and polarization.

Yuri, K3BU.us

High Yuri,

I try again.

Ratiation pattern
As NVIS radiation comes from near 90 degrees elevation, the antenna
receiving the incoming wave will operate at near maximum gain, no
matter the orientation (in horizontal plane) of the dipole. The gain
of a dipole under 75 degrees is less then 1 dB below the maximum.

To orient your antenna to get a nul, you have to use a vertical dipole
(or vertical monopole). So radiation pattern is not of importance.

Polarization,
If the ionosphere would act as a pure mirror reflector, and there was
no free charge, you are right, orientation of both antennas would
matter. As you do not know the amount of polarization change, you
cannot predict the optimum orientation.

Prove it yourself by using a hand held antenna (for example small
vertical loop, or horizontal small dipole). Listen to an NVIS station
(at about 50..100 mile from you) and rotate the antenna around the Z
as. You should do this fast enough to distinguish between fading.
You will find certain orientations with less reception, but the
orientation (with minimum reception) will vary (that can be within a
minute because of the change in overall faraday rotation). You will
seldom find a real nul. This is because of the existence of a more or
less circular component.

If you want to be sure and also want to cover situations in which the
refracted wave is almost linear polarized, you may consider two
(small) antennas (perpendicular to each other) and switch between the
two.

During last year JOTA I had plenty of space to use two half wave
dipoles, but it wasn't worth to do. I checked it with a simple hand
held vertical tuned loop antenna by rotating the antenna round the Z-
axis.

Best regards,

Wim

Rick wrote in
news
On Mon, 09 Apr 2007 23:36:56 +0000, Dave Oldridge wrote:

NVIS propagation is pretty high angle stuff. If you look at the
three dimensional patterns for NVIS antennas you will see that they
have a large lobe at high angles and an almost circular
omnidirectional pattern at those angles. We're looking at 80 degrees
and up mostly here, maybe 70 at the low end....so that antennas are
mainly designed to illuminate the patch of ionosphere directly above
the antenna.

Right. That's my point. So, what I'm claiming ... and trying to get
someone who knows more about this stuff than I do (which is just about
all of you) to confirm or deny ... is that with an NVIS dipole,
someone 100 miles away from me would not be able to perceive the
difference if my antenna was broadside to him or oriented in line with
him. True, or false?

True. Given the vagaries of propagation and the small differences in the
pattern at that angle, he wouldn't notice.

--
Dave Oldridge+
ICQ 1800667