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оригинального документа
: http://www.naic.edu/~astro/RXstatus/Lwide/Lwide_old.shtml
Дата изменения: Unknown Дата индексирования: Mon Feb 4 08:17:26 2013 Кодировка: |
Decomissioned L-wide
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| Frequency Range (GHz): |
1.12 - 1.73
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Name and Number:
L-wide (lbw, 5)
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Measured Sensitivity (K/Jy):
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8.5-11.5*
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Measured System Temp (K):
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34-40*
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Native Polarization:
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Dual Linear**
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Beam Size (at 1415 MHz):
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3.1 x 3.5 arcmin*
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**Note circular polarization is obtained from the receiver by using a hybrid. LCP on the sky comes down on the left-hand rack in the control room, which in the user's manual is referred to as pol A: at the correlator, it occupies the first half of the set of subcorrelators. For VLBI users, this is fed by convention to the BD tracks, unless the user makes some intervention of his own.
NOTE: This receiver has been replaced by a new L-wide receiver in February 2030.
Information on the new receiver can be found here
Recent Events:
The L_wide receiver was removed from the Gregorian at the end of January 2003, at the start of the campaign for realigning the zenith angle track (February 03). It is being replaced by the new L_band receiver. Some of its parts, such as the gain-tube cal unit, are now part of the new receiver.
The position of the feed horn was moved down 3.67 inches (towards the tertiary) on 22 Nov 02, to place its phase center at the focus. This results in a very much flatter gain adjustment curve, and a gain of about 11 K per Jy. The gain curves resulting from data taken between 21 Nov and 31st Dec, and the system performance from the limited number of tracks available links to Phil's page.
The compressor for the cooling lines to this receiver were refurbished in the fall-01;
this is a regular, about two yearly occurrence to try to head off receiver warmups
that can be attributed to compressor failures. In addition, this time a switch was also
fitted to enable the compressors to be reset from the control room after a power dip,
to try to minimize occasions on which the receiver warms up from this, more frequent, cause.
Large scale adjustments were made to the surface of the primary reflector
between 20 Dec 2000 and 11 Jan 2001. Finer adjustments were made thereafter,
with the last quadrant (southeast, which most affects the gain of northern sources)
being the last to be finished in September. All gain curves this year (2001)
therefore have their problems.
| Gain and System Temperature | Cal Values | Beam Maps |
| Polarization | Calibration Schedule | Misc. Calibration Info |
The fitted variation of Tsys with za (in degrees) at 1415 MHz is:--
Currently, our best estimate for the dependence of the gain at 1415 MHz on za and az is:-
-0.20991*cos(az*3) -0.09803*sin(az*3)
where the last term is not significant
Gain(za, az) = 10.85523 - 0.10291*za + 0.01343*(za-14)^2 - 0.00717*(za-14)^3
In units of K per Jansky. The frequency dependence of the gain, and the process used to derive them are
documented under the gain and system temperature button.
electrically switchable filters on the wide-band L-band receiver
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The OMT has a number of resonances, which can greatly affect its performance, and the linearity of
baselines obtained with it. In addition, the OMT is massive, and its thermal inertia causes the
receiver to take about 40 hours to completely cool down to the desired operating temperatures.
Moreover it has never achieved a system temperature of better than about 34 K, whilst a
Tsys of about 25 K was anticipated
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Note: Filters can be moved between the narrow and wide-band L-band receivers
It is wise to check the disposition of the filter you want
lbfb # is the invocation to secure the desired filter
There is no stright through option with this receiver