"Frank's" wrote in message
news:YJhdh.17283$YV4.16290@edtnps89...
wrote in message
ups.com...
It is possible to get nonlinear interactions among electromagnetic
waves in plasmas, but you generally need very large amplitudes to get
nonlinearities to kick in.

I'm guessing that "space modulation" has something to do with multipath
reflections or something; the VOR signal that rotates is going to be
modulated by the buildings, mountains, and so forth around the
transmitter, generally, the "space"

Just a guess; I don't really know anything about VOR.

Dan

Space modulation, in the case of VOR, is produced by a dipole
rotating at 1800 rpm. The rotating dipole pattern produces a
30 Hz amplitude modulation of the VOR omni-directional
pattern. This rotating pattern provides bearing information
to the receiver. The reference 30 Hz is provided by
FM modulation of the omni-directional pattern.

73,

Frank (VE6CB)


I know how a VOR works its the concept of space modulation I dont
understand. How can radiated enery from multiple sources combine in space
and modulate each other. This is as described by the FAA manual. I am
thinking this can nit happen but the modulation takes place only in the
receiver, not out in space as described by the manual.

Jimmie D wrote:

SNIPPED


I know how a VOR works its the concept of space modulation I dont
understand. How can radiated enery from multiple sources combine in space
and modulate each other. This is as described by the FAA manual. I am
thinking this can nit happen but the modulation takes place only in the
receiver, not out in space as described by the manual.



I don't know if the term Space Modulation is applicable to this effect, but the
ionosphere does cause AM modulation.

The atmosphere from sea level up to approximately 300K feet altitude is an
ionized thickness. This ionization peaks at the Paschen altitude of around 200
Kft. The ionization source is the sun. We see this with xray flares and proton
effects [northern lights] and the loss of HF propagation. The lowest levels have
little ionization [C layer, D layer, etc]. At xray peak fluxes we experience
total loss of HF propagation and high absorption of 80/40 meter ground wave signals.

This ionization is not uniform nor is it static. It is quite dynamic and varies
with air density [wind, rain, snow, etc]. The variation in ionization causes
amplitude modulation of signals being propagated through the ionosphere. We
normally experience it as QSB on HF and as flutter on some over the horizon VHF
AM signals [not aurora related].

I had the bad experience of the modulation causing a false trigger in a flight
test vehicle. We had about 5% AM on a near earth telemetry signal. We had to
redesign the detector circuits to accommodate the effect.

Aircraft communications is AM and VHF. I assume, if this effect is Space
Modulation, that it becomes important on weak signal paths.

"Frank's" wrote in message
news:YJhdh.17283$YV4.16290@edtnps89...
wrote in message
ups.com...
It is possible to get nonlinear interactions among electromagnetic
waves in plasmas, but you generally need very large amplitudes to get
nonlinearities to kick in.

I'm guessing that "space modulation" has something to do with multipath
reflections or something; the VOR signal that rotates is going to be
modulated by the buildings, mountains, and so forth around the
transmitter, generally, the "space"

Just a guess; I don't really know anything about VOR.

Dan

Space modulation, in the case of VOR, is produced by a dipole
rotating at 1800 rpm. The rotating dipole pattern produces a
30 Hz amplitude modulation of the VOR omni-directional
pattern. This rotating pattern provides bearing information
to the receiver. The reference 30 Hz is provided by
FM modulation of the omni-directional pattern.

73,

Frank (VE6CB)


Thanks Frank, I thought the FM modulation was caused by doppler shift as a
result of the antenna rotation

wrote in message
ups.com...
Jimmie D wrote:
I was going through some FAA course material on Instument Landing Systems
and the term SPACE MODULATION was mentioned several times. What the heck
is
this.

I believe this was fully explained in a documentary I saw as a kid.
Something about the Q-36 Explosive Space Modulator.

Tim.


Was this Marvin the Martian?

Anyway I found that there truly is no such thing as space modulation. It is
used to form a concept of how ILS beam patterns are formed and all
modulation takes place in the receiver of the aircrafts ILS receiver. A few
years ago The FAA dropped this as a way of teaching ILS concepts.

Imagine that you have a highly directional transmitting antenna and you
spin it at, say, 100 revolutions per second. What would a listener at a
fixed location hear? He would hear a 100 Hz (but non-sinusoidal)
amplitude modulated signal rather than a constant amplitude CW tone. The
shape of the modulation envelope would be dictated by the shape of the
antenna pattern. The spectral content, i.e., sidebands, of the received
signal would be the same as if the wave had been amplitude modulated by
conventional means to produce the same waveshape.

I think that's what they mean.

Roy Lewallen, W7EL

Jimmie D wrote:
I was going through some FAA course material on Instument Landing Systems
and the term SPACE MODULATION was mentioned several times. What the heck is
this. From what I gather signals modulate each other out in space without
benifit of any nonlinear device. I personally beleave this cannot happen but
here is a reference to an FAA document.I assume they know what they are
talking about.

Abstract : The report describes an investigation into the cause of
incompatibility between ground and airborne measurements of VOR space
modulation when using the latest flight inspection receiver, FA-4165:3A. The
effort included a survey of the existing procedures and equipment used
throughout the FAA, an evaluation of the ground measurement technique, and
an evaluation of the airborne measurement technique. The result of the
investigation identified problem areas with both the ground and airborne
techniques.

I suspect that space modulation is more of a concept used to more easily
understand/teach the operation of ILS systems and that actual modulation
takes place in the receiver.

Jimmie

"Roy Lewallen" wrote in message
...
Imagine that you have a highly directional transmitting antenna and you
spin it at, say, 100 revolutions per second. What would a listener at a
fixed location hear? He would hear a 100 Hz (but non-sinusoidal) amplitude
modulated signal rather than a constant amplitude CW tone. The shape of
the modulation envelope would be dictated by the shape of the antenna
pattern. The spectral content, i.e., sidebands, of the received signal
would be the same as if the wave had been amplitude modulated by
conventional means to produce the same waveshape.

I think that's what they mean.

Roy Lewallen, W7EL

Jimmie D wrote:
I was going through some FAA course material on Instument Landing Systems
and the term SPACE MODULATION was mentioned several times. What the heck
is this. From what I gather signals modulate each other out in space
without benifit of any nonlinear device. I personally beleave this cannot
happen but here is a reference to an FAA document.I assume they know what
they are talking about.

Abstract : The report describes an investigation into the cause of
incompatibility between ground and airborne measurements of VOR space
modulation when using the latest flight inspection receiver, FA-4165:3A.
The effort included a survey of the existing procedures and equipment
used throughout the FAA, an evaluation of the ground measurement
technique, and an evaluation of the airborne measurement technique. The
result of the investigation identified problem areas with both the ground
and airborne techniques.

I suspect that space modulation is more of a concept used to more easily
understand/teach the operation of ILS systems and that actual modulation
takes place in the receiver.

Jimmie
Roy I can kind of see this in a VOR with its rotating antenna but in ILS
systems(glideslopes and localizers) there is no moving antenna. They talk
about AM sidebands being formed due to space modulation.

On Sun, 17 Dec 2006 05:13:10 -0500, "Jimmie D"
wrote:

Roy I can kind of see this in a VOR with its rotating antenna but in ILS
systems(glideslopes and localizers) there is no moving antenna. They talk
about AM sidebands being formed due to space modulation.

Hi Jimmie,

I worked on this gear, and more, 30 years ago. Any discussion of
space was physical space. I was involved only with the
instrumentation, but the system specification is characterized in
terms of "signal-in-space." As such, the modulations vary by the
aircraft's position in airspace. This can be in terms of distance,
bearing, slope, or path. In some regions of space, the modulations
change from dash to dash-dot to dots. Shared with these are phase
relationships in both modulation and beam coverage. Testing of these
system parameters is tightly controlled so as to not create
hazardously misleading information to general aviation.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Sun, 17 Dec 2006 05:13:10 -0500, "Jimmie D"
wrote:

Roy I can kind of see this in a VOR with its rotating antenna but in ILS
systems(glideslopes and localizers) there is no moving antenna. They talk
about AM sidebands being formed due to space modulation.

Hi Jimmie,

I worked on this gear, and more, 30 years ago. Any discussion of
space was physical space. I was involved only with the
instrumentation, but the system specification is characterized in
terms of "signal-in-space." As such, the modulations vary by the
aircraft's position in airspace. This can be in terms of distance,
bearing, slope, or path. In some regions of space, the modulations
change from dash to dash-dot to dots. Shared with these are phase
relationships in both modulation and beam coverage. Testing of these
system parameters is tightly controlled so as to not create
hazardously misleading information to general aviation.

OM,

I'd appreciate any pointers you have to the FAA reference material that
defines "Space Modulation". Google shows only links to lists of training
courses that the FAA conducts, and references to "Pulse space
modulation", which I assume is a different thing.

TIA.

73,

William

(No cc: of ng posts needed, thanks)

--
A little learning is a dang'rous thing;
Drink deep, or taste not the Pierian spring;
There shallow draughts intoxicate the brain,
And drinking largely sobers us again.
-- Alexander Pope, Essay on Criticism

nonoise wrote:
Richard Clark wrote:

On Sun, 17 Dec 2006 05:13:10 -0500, "Jimmie D"
wrote:

Roy I can kind of see this in a VOR with its rotating antenna but in
ILS systems(glideslopes and localizers) there is no moving antenna.
They talk about AM sidebands being formed due to space modulation.


Hi Jimmie,

I worked on this gear, and more, 30 years ago. Any discussion of
space was physical space. I was involved only with the
instrumentation, but the system specification is characterized in
terms of "signal-in-space." As such, the modulations vary by the
aircraft's position in airspace. This can be in terms of distance,
bearing, slope, or path. In some regions of space, the modulations
change from dash to dash-dot to dots. Shared with these are phase
relationships in both modulation and beam coverage. Testing of these
system parameters is tightly controlled so as to not create
hazardously misleading information to general aviation.


OM,

I'd appreciate any pointers you have to the FAA reference material that
defines "Space Modulation". Google shows only links to lists of training
courses that the FAA conducts, and references to "Pulse space
modulation", which I assume is a different thing.

TIA.

73,

William

(No cc: of ng posts needed, thanks)

Do a GOOGLE search on "Space Modulation" You will find the occasional
pearl among the trash. There is an article about VOR's and Space
Modulation.
What follows is exactly what I understood about the contents: THE, AND, etc.
In other words nothing. HI HI...

Dave N

On Sun, 17 Dec 2006 13:59:08 -0500, nonoise
""william_warren_nonoise\"@speakeasy.(nonoise)net " wrote:

FAA reference material that
defines "Space Modulation"

Hi William,

There is no definition because it isn't part of the argot. The point
of my posting is that the Space of Space Modulation is physical space,
an area or volume in the flight path where all signals are targeted.
This is not about mixing, non-linear or otherwise. It is also not
about modulation waveforms except in how they are intercepted and
recognized by existing equipment (and thus giving rise to HMI,
hazardously misleading information).

It is not that there is anything "in" space that is doing any
modulation. There is nothing inherent "about" space that affects
modulation. Space itself does not modulate. There is no modulation
that requires space to complete it (except in the classic sense of
propagation).

There is VOR space.
There is ILS space.
There is TACAN space.
and on and on and on. Each is overlapping modulation in ostensibly
the same space. Thus we have VOR space Modulation....

73's
Richard Clark, KB7QHC