"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

"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

"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

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

"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