"J. Mc Laughlin" writes:

In any case, I suggest you avail yourself of the benefit of raising
whatever you use to a height of something like 0.2 WL and less than 0.3 WL.

Or, in the case of 80 m, between 16 and 24 m up (for the metric
challenged: between 50 and 75 ft). Excellent for those who can, but
most can't.

73 de LA4RT Jon

On 10 abr, 06:34, Rick wrote:
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?

Hello Rick,

At 100 miles distance, the TOA is almost vertical (maybe 75 degr), so
with respect to signal strength, it is practically impossible to
detect whether the antennas are broad side. Because of the distance,
ground wave propagation loss is far higher with respect to NVIS
propagation loss under these circumstances.

One would mention polarization of the waves going up and down. I
would not matter about this. These low frequencies are strongly
affected by faraday rotation. On the way up and down, the polarization
rotates several times and several wave fronts do exist.

While you transmit (nearly vertical) with linear polarization, the
down coming wave may have a strong circular component.

With respect to the radiation pattern, you are right, the differences
in pattern are minimal below 30 feet. However the overall efficiency
is strongly depended on antenna height and soil properties. I did some
simulation and practice. I made a short document of it (for JOTA
porpuse), however the document is in Dutch Language (http://
www.tetech.nl/divers/NVISantenneNL1.pdf). Maybe you can get some
useful info out of it. At low heights, much power is dissipated into
the ground (resulting in a useful bandwidth).

Best Regards,

Wim
PA3DJS

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?

Absolutely true. Any difference would be insignificant. The path
elevation is about 79 degrees for that path.

--
Dave Oldridge+
ICQ 1800667

LA4RT Jon ?Q?K=C3=A5re?= Hellan wrote in
:

"J. Mc Laughlin" writes:

In any case, I suggest you avail yourself of the benefit of
raising
whatever you use to a height of something like 0.2 WL and less than
0.3 WL.

Or, in the case of 80 m, between 16 and 24 m up (for the metric
challenged: between 50 and 75 ft). Excellent for those who can, but
most can't.

A horizontal quad loop at 50 feet is almost ideal for NVIS.


--
Dave Oldridge+
ICQ 1800667

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:
"Wimpie" wrote in message


Hello Rick,

At 100 miles distance, the TOA is almost vertical (maybe 75 degr), so
with respect to signal strength, it is practically impossible to
detect whether the antennas are broad side. Because of the distance,
ground wave propagation loss is far higher with respect to NVIS
propagation loss under these circumstances.

One would mention polarization of the waves going up and down. I
would not matter about this. These low frequencies are strongly
affected by faraday rotation. On the way up and down, the polarization
rotates several times and several wave fronts do exist.

While you transmit (nearly vertical) with linear polarization, the
down coming wave may have a strong circular component.

With respect to the radiation pattern, you are right, the differences
in pattern are minimal below 30 feet. However the overall efficiency
is strongly depended on antenna height and soil properties. I did some
simulation and practice. I made a short document of it (for JOTA
porpuse), however the document is in Dutch Language (http://
www.tetech.nl/divers/NVISantenneNL1.pdf). Maybe you can get some
useful info out of it. At low heights, much power is dissipated into
the ground (resulting in a useful bandwidth).

Best Regards,

Wim
PA3DJS

"Dave Oldridge" wrote in message
9...
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?

Absolutely true. Any difference would be insignificant. The path
elevation is about 79 degrees for that path.

--
Dave Oldridge+
ICQ 1800667

Absolutely???

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

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.

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

"Yuri Blanarovich" wrote in
:


"Dave Oldridge" wrote in message
9...
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?

Absolutely true. Any difference would be insignificant. The path
elevation is about 79 degrees for that path.

--
Dave Oldridge+
ICQ 1800667

Absolutely???

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?

And they don't actually work on NVIS signals unless you use them to
measure elevation, in which case they point fairly high up.

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.

You're assuming the ionosphere doesn't rotate the signal (or even render
its polarization elliptical). Whether that's happening or not will
likely depend on conditions at the time. But if it doesn't, then it
doesn't matter which way the antennas are oriented in azimuth so long as
they are both oriented the same.

--
Dave Oldridge+
ICQ 1800667

"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?

73 Yuri, K3BU

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