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From: Archimedes Plutonium on 6 Jun 2010 15:17


David Bernier wrote:
> Mike Dworetsky wrote:
> > Archimedes Plutonium wrote:
> >> pete wrote:
> >>> Archimedes Plutonium wrote:
> >>>
> >>>> radio waves instead of radar waves.
> >>>
> >>> What's your perceived difference between the two?
> >>>
> >>> (RADAR = Radio Detection And Ranging)
> >>>
> >>> --
> >>> pete
> >>
> >> Wavelength of some typical EM spectrum:
> >>
> >> Radar 10km to 1 km
> >>
> >> AM 1 km to 100 m
> >>
> >> FM 10 m to 1 m
> >
> > You have a sadly lacking understanding of radar, to say the very least.
> > Most radar operates at wavelengths less than one metre; many systems
> > operate at a few cm. For example, the K-band used by police to detect
> > car speeds operates between 1.1 and 1.7 cm.
> >
> > A few operate at longer wavelengths (over 1m) for specialized purposes.
> >
> >>
> >> The difference I wanted to point out is that the radar for Doppler
> >> radar (with its alleged
> >> Doppler shift) is all assumption that a Doppler shift took place. So
> >> it is an imaginary Doppler
> >> shift with no proof of a shift having occurred.
> >
> > You tried this on in court to defend your speeding citation, I take it?
> > How did that go?
> >
> >>
> >> The AM and FM on the other hand has the receiver inside the moving car
> >> or the moving
> >> Space Station (whether they can pick up the AM and FM stations). Here,
> >> the Doppler
> >> shift is either existing or nonexisting, since the radio would have to
> >> be fine tuned
> >> as per changing of the speed of the vehicle and direction of the
> >> vehicle.
> >
> > Do they listen to Earthbound FM radio on the ISS?
> >
> >>
> >> The point I am making is that the Radar operation does not answer the
> >> question of whether
> >> a Doppler shift in fact exists, but imposes an alleged Shift took
> >> place. The Radio as
> >> receiver is the piece of equipement that answers the question of
> >> whether a Doppler shift
> >> exists in the first place.
> >
> > So it's all a conspiracy?
> >
> >>
> >> So now, let us say someone rigged a Radar that was AM radio waves and
> >> zapped a
> >> car moving at a fast speed away. Would the AM radio have to make any
> >
> > AM waves are long, hundreds of metres, and are not used for radar in
> > police radar instruments.
> >
> >> adjustments compared to the
> >> same car if stationary? What the radio proves, the Radar only assumes,
> >> is that the Radio
> >> can actually detect whether a Doppler shift had occurred, because the
> >> radio would have
> >> to make adjustments, depending on whether it is a coming towards or
> >> away and how fast.
> >>
> >> As far as I know, no radio has ever needed a adjustment because of the
> >> speed of the vessel
> >> containing the radio. That means, EM waves have no Doppler effect.
> >>
> >
> > Or they are too small to need to be taken into account at shipping and
> > motoring speeds.
>
> But not when a probe (Huygens) that descended to Titan had to
> relay its data to the Cassini orbiter...
>
> Ref.:
> < http://spectrum.ieee.org/aerospace/space-flight/titan-calling/8 >
>
> and more ...
>
> --------------------Excerpt from IEEE Spectrum, October 2004 ----------------
> << The board discovered that Alenia Spazio SpA, the Rome-based company that
> built the radio link, had properly anticipated the need to make the receiver
> sensitive over a wide enough range of frequencies to detect Huygens's carrier
> signal even when Doppler shifted. But it had overlooked another subtle
> consequence: Doppler shift would affect not just the frequency of the carrier
> wave that the probe's vital observations would be transmitted on but also the
> digitally encoded signal itself. In effect, the shift would push the signal out
> of synch with the timing scheme used to recover data from the phase-modulated
> carrier.
>
> Because of Doppler shift, the frequency at which bits would be arriving from
> Huygens would be significantly different from the nominal data rate of 8192 bits
> per second. As the radio wave from the lander was compressed by Doppler shift,
> the data rate would increase as the length of each bit was reduced.
> "The guys who pushed the original test through are heroes" --John Zarnecki
>
> Although the receiver's decoder could accommodate small shifts in the received
> data rate, it was completely out of its league here. The incoming signal was
> doomed to be chopped up into chunks that didn't correspond to the actual data
> being sent, and as a result the signal decoder would produce a stream of binary
> junk. The situation would be like trying to watch a scrambled TV channel--the
> TV's tuned in fine, but you still can't make out the picture. >>
> -------------------------- from IEEE Spectrum, October 2004 ----------------
>
> Please see:
> "Titan Calling" by James Oberg about
> the Cassini-Huygens radio link bug and
> how a work-around was found ...
>
> here:
> < http://spectrum.ieee.org/aerospace/space-flight/titan-calling/6 >
> and previous & later pages (very nice article).
>
> David Bernier


And the reason they ended up with an end result of scrambling digit
code was because
they assumed a Doppler Shift and compensated for a Doppler shift. If
instead they
had reasoned no Doppler Shifting occurred, their picture would be
crystal clear.

The only compensation in astronomy for light traveling is that due to
scattering and
refraction. So the distance of light travelling to Titan needs only
compensation for
scattering and refraction. If you compensate for Doppler shifting you
make the picture
worse.


Archimedes Plutonium
http://www.iw.net/~a_plutonium/
whole entire Universe is just one big atom
where dots of the electron-dot-cloud are galaxies
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