Re: G-Whip Returns


"Spike" <Aero.Spike@S&T.invalid> wrote in message
news:06mq34hq779a3tsljp3eg40tkg1gor90qk@xxxxxxxxxx
Unless something has changed, GPS units
derive speed by comparing changes in position and time- effectively a
differentiation (delta position / delta time). I assume you know the
problems associated with using differentiation on measurements?

The third elephant in the room.....

Once locked on, the GPS uses dopper to determine speed.


As I said "unless something has changed". I will elucidate.

The RX is given a "preset" set of SV data- inc. approx. SV position and
Doppler (I can't recall if the latter is given directly or as a velocity to
permit local calculation of Doppler.) However, having "locked on" (to use
your phrase), the RX LO can be tracked to find the relative change in SV to
rx velocity but this doesn't "fix" any original error in the estimate (more
simply, with both moving how do you know which one changed its velocity to
cause a change in the Doppler shift. With a large (relative) velocity
difference and the majority of the absolute velocity being associated with
the SV, the error budget would be a tad biased).

GPS does not use Doppler to find position, it is a triangulation technique
based in distance measurement. The older Transit system did use Doppler but
that is probably now defunct- it was already being phased out when I was
working on "NavStar" augmented systems in the mid 80s. As I recall, it did
last a bit longer than planned (I think due to problems getting the GPS
constellations "complete").



--
73
Brian, G8OSN
www.g8osn.org.uk




.

Relevant Pages

  • Re: Farmers in orbit
    ... Mondian anomalous velocity is towards an artificially defined origin, ... Hubble shift represents a recession velocity exactly equal to Doppler ... that also may show up as an acceleration toward the origin. ... The clock on pioneer is running fast. ...
    (uk.business.agriculture)
  • Re: Aberrations from the relativistic aberration of light
    ... the photon does not move at a velocity of c with ... | the formula is just the kinematic time dilation of the observer. ... the relativistic Doppler effect. ... If you love Galilean relativity ...
    (sci.physics.relativity)
  • Re: Antennas led astray
    ... but consider that the red shift frequencies ... Doppler effect is readily observable at audio and RF wavelengths. ... Any effects that alter Doppler at light wavelengths should also be noticeable at to wavelengths. ... we're A. System B is moving away from us at relativistic velocity. ...
    (rec.radio.amateur.antenna)
  • Re: Einsteins Relativity Disregards the Doppler Effect?
    ... an intensed doppler effect the light would no longer be observed as ... sound wave (if moving away from observer) or alpha wave (if moving ... observer approaching a source of light with the velocity c, ...
    (sci.physics.relativity)
  • Re: Integration and derivation
    ... damper forces in Adsms/Car simulation package. ... The velocity between two ... An alternative is "automatic differentiation", ...
    (comp.lang.fortran)