Wideband Receivers

Hiroshige Yoshida
Caltech Submillimeter Observatory

1  Tuning Wideband Receivers

For instructions on how to tune "Frank Rice's" receiver, take a look at "Jin and Jenny's Instructions for Frank's Receiver." Instructions for "Barney" will be added soon.

2  Taking Data

2.1  4 GHz Array AOS and IF Processor

See "Köln 4 GHz Array AOS" for general instructions on how to set up and shut down the Array AOS and the IF Processor.

2.2  1 GHz FFTS

See "MPIfR 1 GHz FFTS" for general instructions on how to use this FFTS.

2.3  8 GHz FFTS

See "CASIMIR 8 GHz FFTS" for general instructions on how to use this FFTS.

2.4  Configuring LO for Wideband Receivers

The nominal center of the IF is 6 GHz. Gunn LO chains of "Barney" and "Frank Rice's" receiver use one of the phase lock modules from SMA. For example, the following command explicitly selects "Frank Rice's" receiver, which is connected to the 4-8 GHz IF input A of the IF Processor, to observe in the 12CO(J=2→1) line:
UIP> LO 12CO2-1 /RECEIVER RX230X /IF_FREQUENCY 6.0 /LOCK_LOOP SMA
The current Gunn LO chain for "Frank Rice's" receiver has a tripler at the end, so the multiplier harmonic number has to be set to 3. The harmonic number for the original synthesized LO chain is 15. The Gunn LO chain for "Barney" has a quadrupler.
In most cases, it is desirable to center a target line in one of the subbands of the array AOS rather than to place it in between two. To do so, either change the IF from 6 GHz to where in the 4-8 GHz IF passband the line should appear or offset the line from the nominal IF center using frequency offset or velocity offset. For example, the following command will move the IF center to the middle of the second (5-6 GHz) subband:
UIP> LO /IF_FREQUENCY 5.5
When the synthesized LO is used instead of the Gunn LO chain on "Frank Rice's" receiver, set the phase lock loop to NONE:
UIP> LO /LOCK_LOOP NONE
For the SMA-JCMT-CSO eSMA experiments with "Frank Rice's" receiver, set the IF to 5 GHz, the phase lock loop to SMA, and the multiplier harmonic number to 3 (as of October 31, 2005):
UIP> LO /IF_FREQUENCY 5 /LOCK_LOOP SMA /MULTIPLIER 3

2.5  Reconfiguring LO for Narrowband Receivers

The nominal center of the IF is 1.5 GHz. The Side Cabin receivers use the default phase lock loop module. The 850 GHz receiver uses the SMA phase lock loop module, like the wideband receivers. For example, the following command selects the 230 GHz receiver in the Side Cabin to observe in the 12CO(J=2→1) line:
UIP> LO 12CO2-1 /IF_FREQUENCY 1.5 /LOCK_LOOP DEFAULT

2.6  Pointing

The pointing file to be used with "Barney," when it is mounted at the Cassegrain focus, is BARNEY_CASS:
UIP> POINTING BARNEY_CASS
The pointing file for "Frank Rice's" receiver is Z_REX when it is mounted at the Cassegrain focus:
UIP> POINTING Z_REX
and FRANK_N2 when it is mounted at the right Nasmyth focus (N2):
UIP> POINTING FRANK_N2
The pointing accuracy of the telescope should be checked using the FIVE_POINT command in the same way as other receivers.
Although an entire 4 GHz passband can be used to point in continuum, it is usually desirable to limit the integration range, for example to avoid spectral features caused by the atmosphere. The following command will use 1400 channels from the first subband of the array AOS, centered at 1000, to perform a 15′′ five-point measurement in continuum:
UIP> FIVE_POINT 15 700 /AOS5 /ONE_OFF /CENTER 1000
Array AOS channels are numbered from 1 to 2048 for each subband in CLASS data files but are numbered from 1 to 8192 in UIP. If a spectral line to use for pointing is in the second, third or forth subband, channel numbers for baseline windows need to be offset by 2048, 4096 or 6144, respectively. For example, the following command will set baseline windows between channels 872 and 972 and between channels 1032 and 1132 of the second subband:
UIP> SPECTROMETER 5 /BASELINE 2920 3020 3080 3180

3  Quirks and Workarouds

3.1  Array AOS Attenuators

An attenuation of each subband of the array AOS can individually be changed using the ATT1, ATT2, ATT3, and ATT4 macros.
When a strong spur is present within a certain subband, a majority of CCD pixels in that subband can grossly be under-illuminated after the ADJUST_ATTN command. The attenuation of the affected subband can manually be reduced at the expense of some additional unusable channels near the spur (due to saturation of CCD pixels). The following procedure is an example of how to set the attenuators when there is a spur in the forth subband:
UIP> RETICON
UIP> ADJUST_ATTN
UIP> ATT4 10
UIP> DB /AOS5 /ADD 1
UIP> NO_RETICON

3.2  Temperature Calibration of Array AOS

When the difference between the hot load level and the sky level is more than 3 dB (i.e., when a y-factor on the sky is more than 2), manually adjust the attenuators on the sky, add an extra 1 dB or two (y-factor of 2.7 ⇔ 4.3 dB), then take a TCAL scan:
UIP> ADJUST_ATTN
UIP> DB /AOS5 /ADD 1
UIP> CALIBRATE /NOATTENUATOR


File translated from TEX by TTH, version 4.03.
On 25 May 2012, 09:34.