58 lines
3.2 KiB
Plaintext
58 lines
3.2 KiB
Plaintext
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A text box entitled Astronomical Data provides information needed for
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tracking the sun or moon, compensating for EME Doppler shift, and
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estimating EME Doppler spread and path degradation. Toggle the
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*Astronomical data* on the *View* menu to display or hide this window.
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image::AstroData_2.png[align="center",alt="Astronomical Data"]
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Available information includes the current UTC *Date* and time; *Az*
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and *El*, azimuth and elevation of the moon at your own location, in
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degrees; *SelfDop*, *Width*, and *Delay*, the Doppler shift, full
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limb-to-limb Doppler spread in Hz, and delay of your own EME echoes in
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seconds; and *DxAz* and *DxEl*, *DxDop*, and *DxWid*, corresponding
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parameters for a station located at the *DX Grid* entered on the main
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window. These numbers are followed by *Dec*, the declination of the
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moon; *SunAz* and *SunEl*, the azimuth and elevation of the Sun;
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*Freq*, your stated operating frequency in MHz; *Tsky*, the estimated
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sky background temperature in the direction of the moon, scaled to the
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operating frequency; *Dpol*, the spatial polarization offset in
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degrees; *MNR*, the maximum non-reciprocity of the EME path in dB,
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owing to a combination of Faraday rotation and spatial polarization;
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and finally *Dgrd*, an estimate of the signal degradation in dB,
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relative to the best possible time with the moon at perigee in a cold
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part of the sky.
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On the higher microwave bands, where Faraday rotation is minimal and
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linear polarization is often used, spatial offset will reduce signal
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levels. Some stations have implemented mechanical polarisation
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adjustment to overcome this loss, and the amount of rotation needed is
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predicted in real time by the value of *Dpol*. Positive Dpol means
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that the antenna should be rotated in a clockwise direction looking
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from behind the antenna towards the moon. For a dish antenna, the
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feed should similarly be rotated clockwise looking into the mouth of
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the feed. A negative value for Dpol means anticlockwise rotation.
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The state of the art for establishing three-dimensional locations of
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the sun, moon, and planets at a specified time is embodied in a
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numerical model of the solar system maintained at the Jet Propulsion
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Laboratory. The model has been numerically integrated to produce
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tabular data that can be interpolated with very high accuracy. For
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example, the celestial coordinates of the moon or a planet can be
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determined at a specified time to within about 0.0000003 degrees. The
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JPL ephemeris tables and interpolation routines have been incorporated
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into _WSJT-X_. Further details on accuracy, especially concerning
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calculated EME Doppler shifts, are described in {lunarEchoes} for
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November-December, 2016.
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The sky background temperatures reported by _WSJT-X_ are derived from
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the all-sky 408 MHz map of Haslam et al. (Astronomy and Astrophysics
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Supplement Series, 47, 1, 1982), scaled by frequency to the -2.6
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power. This map has angular resolution of about 1 degree, and of
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course most amateur EME antennas have much broader beamwidths than
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this. Your antenna will therefore smooth out the hot spots
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considerably, and the observed extremes of sky temperature will be
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less. Unless you understand your sidelobes and ground reflections
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extremely well, it is unlikely that more accurate sky temperatures
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would be of much practical use.
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