"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.