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: http://www.naic.edu/~phil/callbn/lbncalvaluedec00.html
Дата изменения: Mon Mar 4 17:06:59 2002 Дата индексирования: Tue Oct 2 09:48:27 2012 Кодировка: Поисковые слова: п п п |
The lbn cal was injected via a waveguide coupler into the waveguide that connects the orthomode transducer to the dewar. For this measurement, the orthomode transducer was removed and a waveguide transition was installed. A cold load (at 70 K) via a 4 foot cable was connected to a 20 db directional coupler. This coupler was connected to the waveguide transition. The standard diode was connected to 18 db of attenuation and then into the coupled port.After the measurement, the insertion loss from the standard diode to the output of the coupler was measured over the frequency range 1200 to 1400 Mhz. The plots show the results of the measurements:
The observing setup was 4 25 Mhz bands on the correlator with a 15 second integration time. The 4 step observing sequence was (15 seconds at each step): calOff, calOn, calOff, standard On. After each sequence the frequency was stepped by 100 Mhz to cover 1200 to 1600 Mhz. The entire frequency band was measured 3 times.
stdDegK=10^(diodeEnr(freq) + attnCouplerInsertionLoss(freq) -.1)*.1)*290.
The lbnCal was then computed as:
lbnDegK= (lbnCalon-lbnCalOff)/(stdCalOn-stdCalOff) *stdDegK
The measurement assumes the gain of the system remains constant over the 1 minute cycle. The repeatability of the measurements attests to this.
The major uncertainty in the measurement is in the standard diode ENR and the insertion loss of the waveguide transition. The .1 db transition may be a bit low at some frequencies. This would overestimate the lbn cal value by a few percent (mainly at the higher frequencies).
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The data has been included in the idl routines that
return the system temperature. They can also be found in the file: /share/obs4/rcvm/cal.datR6.
Note:13dec01.. There was a mistake
in the original computation of the cal value.. When interpolating the diode
enr I used : delta(enr)/delta(freq) + freq0.. I inadvertantly used the
enr at 2000 rather than 1 Ghz for freq0. The above values are the correct
ones. The old incorrect values can be seen here: (cals
with 6% error).
processing: x101/001218/lbncal.pro
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