RadioBanter - View Single Post - Stealthy 'dual-CP' emissions (more TV channels)

July 17th 04, 10:55 PM

On 17 Jul 2004 13:27:03 -0700, (J. Harvey) wrote:
One of my assumptions is that the RHCP and LHCP can operate in
complete isolation of each other. DBS satellites (for example) use
RHCP and LHCP to double their bandwidth, just like FSS satellites use
H and V. I have not heard anything about the DBS RHCP transponder
having to worry about the LHCP transponder. I haven't heard any
mention of nulls suddenly appearing and disappearing in the downlink

That is because the nulls occur orthogonally to (and not along) the
path. ... At least in the sense of your thought-experiment.

passband as the two senses happen to coincide, out of phase. I haven't
heard about the CP being converted to linear and causing interference
(at -3dB) in the other CP mode.

And possibly for a very good reason: the earth is thousands of miles
away where the subtended arc of the service region precludes more than
a few degrees difference in path length/delay. The initial phase
balance is preserved by geometry.

If they cancel out, then where does the energy go? Make it a mega-watt
each and follow the smoke. If they combine in the vacuum of space,
where is the smoke?

Hi Jeff,

This is just a tarted up version of the multipath phenomenon otherwise
called the Fresnel Zone which, in turn is an example of the optics
display of Newton's rings. If the earth were flat (a presumption of
modelers), then you would observe concentric rings around the service
area that were alternately hot then cold. The earth isn't flat, but
that doesn't cast this effect into the unfathomable, it simple
distorts the progressively outer rings' widths.

73's
Richard Clark, KB7QHC