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

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



Sounds like it would need my set of "imaginary numbers" to define ...

Regards,
JS

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

The only context that I have seen 'Space Modulation' refered to is where
information is conveyed by a 'lack of signal'. ie the length of silence
conveys information.

Reagrds
Jeff

Jeff wrote:
The only context that I have seen 'Space Modulation' refered to is where
information is conveyed by a 'lack of signal'. ie the length of silence
conveys information.

Reagrds
Jeff



Jeff:

Darn little info in the silence. Just means the aliens got tired
chatting, or else there is a coffee break going on. straight face

Regards,
JS

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


No, I know it has nothing to do with things like that,it is as described in
the FAA lit a normal process of forming the ILS radiation patterns and
applies to VOR, Glide slopes and localizers. Google doesnt help much on the
subject.and I ve gone thru the indexs of about 20 radio and antenna books
without finding anything on it.

Jimmie D wrote:

No, I know it has nothing to do with things like that, ...

Jimmie:

Just having a bit of fun. I am only familiar with "space modulation"
when it comes to modems, as much data is contained in the key off mode,
and the length of time key off occurs, as in the key on condition and
its length of time (at least in one method of data transfer I am
familiar with.)

Whether there is any relationship of one to the other is a mystery to
me--like I said, just poking a bit of fun.

Regards,
JS

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)

"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.