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оригинального документа
: http://www.naic.edu/~astro/RXstatus/430ch/430ch.shtml
Дата изменения: Unknown Дата индексирования: Sun Feb 3 22:57:27 2013 Кодировка: |
430 MHz Carriage House Receiver
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Basic Information | Calibration & Beam Parameters RFI Situation Recent Events Receiver History Contact Info |
| Frequency Range (GHz): |
0.425-0.435
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Name and Number:
430ch (Rx no. 100)
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Measured Sensitivity (K/Jy):
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20 (*)
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Measured System Temp (K):
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~120 (including sky)(*)
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Native Polarization:
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Dual Circular
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Beam Size (at 0.430 GHz):
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9.5 x 8.5 sq. arcminutes
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Available Filters:
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10 MHz centered at 430 MHz
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Warnings and Important Notes:
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click here |
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a) Re-select the receiver using the GUI. In the new GUI, you have to
press the button saying "select receiver now".
b) If there is still no signal, check (or ask the operator to
do so) the CRR2/LRR1/LRR2 LO switch in Rack 3-4. This should be in
the "Int" position.
c) Another switch to check is the 20 MHz gated power switch in
Rack 3-4. This should be ON, when that happens, a green LED is also
turned on.
2. Calibration & Beam Parameters:
| Gain and Tsys | Cal Values | Beam Maps | Polarization | Misc. Info |
To see an up-to-date plot of Tsys, just type tsys on
your terminal after logging into Arecibo's computer network. Type
tsysplot,r100 at the IDL prompt to see the plot for the 430 MHz CH receiver.
CAL strengths are NOT controlled under computer/GUI, but need to be set manually
(remote observers would need to request the operators accordingly).
It is quite likely that the settings used by the last user of this CAL may define the default
setting, and it is important to check & select them as desired. The top-most panel
in Rack 8 (i.e. 8-1) has a pair of rotary switches (one per each of the two polarization channels)
to set the cal strength (presumably by changing attenuation).
The CAL level choices are different for the two polarization channels, and they are
indicated on the panel. The values as of 15th November 2004 are listed here.
Manual selection of CAL TEMPERATURE on Rack 8-1 panel
Switch position
(going clock-wise)CAL for "CRR1,2,3 - LRR1"
channel (in degrees K)CAL for "LRR2"
channel (in degrees K)
1
181.5
123.0
2
98.9
62.0
3
47.5
31.0
4
31.0
15.7
Latest T_CAL/T_sys measurements etc. & general receiver history
Not available. However, information on the coma parameter, sidelobe strength, and beam efficiency can be found
here.
Native Polarization: Dual Circular
To do the calibration of this receiver, people have to do some
cabling.
More information on calibration techniques can be found in Chris
Salter's "Note relevant to Spectral Line User's", which can be found
here.
Depending on RADAR system requirements, the receiver is switched
between "cryogenic" and "room temperature" amplifiers. Tsys is
normally measured at the "STOW" position and with both amplifiers.
Recent measurements can be found in the receiver
log.
Note that Tsys depends on the antenna temperature due to the Sky
(i.e., Tsys = Treceiver + Tsky) and is strongly dependent on the
zenith angle of the observation.
Attempts were made during the first week of May 2003 to resolve this problem by adding a bandpass cavity filter offering more attenuation at the carrier frequencies as well as by replacing then existing amplifiers with ones with larger dynamic range. Subsequent tests and azimuth scans revealed that this in-band RFI was still present and was particularly strong in certain azimuth ranges (with a peak around 120 deg. azimuth). See above link for more details.
A low loss bandpass filter with notches at 475 and 520 Mhz was placed in front of the gregorian dewar for polA at the beginning of October 2004 (see details here). This knocks down the TV station signals to a level that they will not create intermods in the dewar. The filter has effectively removed the intermods. Similar filters have been installed in February 2005 on the 430 MHz CH receiver (both polarizations).
For updated info on the maintenance of this receiver, look at the electronics department receiver log.
This is one of the oldest receivers still operating at the Arecibo radio telescope, and it is still the one that provides the largest gain. The problem of such a wide illumination pattern is that away from zenith, the receiver illuminates a lot of the 300 K ground, causing a large drop in gain and a steep increase in system temperatures. While the problem with decreasing gain cannot be dealt with (unless the primary surface is expanded...), the introduction of a ground shield during the recent Arecibo upgrade should have improved the situation of the Tsys for pointings away from the zenith. The plot below is from a calibration made in 1989. It shows that the gain curves have not changed much, as expected, since the main reflector retains its size. The degradation for zenith angles near 20 degrees compared to zenith is smaller in 2001 than in 1989, here we can see the improvement caused by the ground screen.
For further information on this receiver, please contact Aaron Parsons at