| Measurement of amplitude passband of the single-baseline interferometer
| Y-factor and Tsys vs. IF frequency on Feb 18
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| Mean Tsys compared to correlated amplitude vs. IF frequency on Feb 18
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| Y-factor vs. IF frequency on Feb 16
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| Mean Tsys compared to correlated amplitude vs. IF frequency on Feb 16
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| Four pages put together into one document
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Description of ATF LO chain and IF downconversion on the 3mm evaluation receivers: hand-drawn block diagram
Noise temperature vs. frequency:
unit #1
unit #2
| 1. The standard observing frequency at the ATF is 103.83375 GHz.
2. The HEMT amplifier's response is broad (say 80-112 GHz). Its output goes to a bandpass filter from 82-110 GHz.
3. LO1 is ultimately generated by the slave laser, which is locked to 85.8 GHz.
4. The laser output is mixed with the FLOOG at 31.5MHz to produce 85.7685 GHz which is LO1.
5. LO1 provides a USB conversion. This mixer works well over an IF range of 14-22 GHz. The specific 2GHz piece of the HEMT output that is typically observed (102.83375-104.83375) is mixed down to 17.06525-19.06525.
6. The intermediate LO is at 12.375+0.033 = 12.4080 GHz, which provides a USB conversion of the prior band to 4.65725-6.65725 GHz.
7. LO2 is generated by a comb + fine tuning syntheser (8.6250+0.03225=8.65725 GHz), which provides an LSB conversion down to 2.00-4.00 GHz.
8. The sampler operates from 2-4 GHz and effectively provides an LSB conversion down to 0-2 GHz, as seen in the correlator output.
9. Due to an even number of LSB downconversions, the sky frequency increases in the same direction as correlator channel number.
Note 1: The high IF range (14-22 GHz) emerging from the LO1 mixer
effectively prevents DSB response from the HEMT. That is, even if you
tuned LO1 as high as 96 GHz, you would see 82 and 110 at the same spot
in the IF, but these are the edges of the bandpass filter. So, for
LO1 > 96 GHz, the HEMT is an LSB receiver, and for LO1 < 96 GHz, the
HEMT is a USB receiver.
Note 2: There is a plan to remove the intermediate LO in order to enable
DSB response to test the 90 degree phase shift (sideband separation ability)
of the correlator. In this case, the 10-12 GHz IF range would be used
ahead of the LO2 mixer, as the LO1 mixer can be made to work in this
range (which is outside of its 14-22 GHz spec).
If one wanted to cover the same sky frequency range
as before, then LO1 would need to be set to 103.833-11 = 92.833 GHz, but
there would be DSB response in the 10.0-10.833 GHz part of the IF.
To avoid this, presumably one would choose to observe frequency ranges <= (102-104).
|
| Tuning to CS(2-1) at the ATF
| Overview:
Using the same settings of LO2 and the
intermediate LO,
the CS line can be placed near the center of the correlator band simply by
moving the slave laser to 80.0 GHz. When combined with the FLOOG, LO1 is
79.9685. With this setting, the range 97.03375-99.03375 is downconverted to
17.06525-19.06525. The intermediate LO of 12.4080 then moves this range
to 4.65725-6.65725. Finally, LO2 at 8.65725 converts this range down to
2.000-4.000. The sampler then effectively mixes this down to 0.0-2.0 GHz,
as displayed on the CorrGUI. This tuning places the CS line at 97.981 GHz at
IF = 0.94725 GHz = channel 120.25 (neglecting V_lsr and Earth motions).
Instructions
1. First tune as you normally would to 103.83375 (which uses the slave laser at 85.8 GHz).
2. Then issue the PSI script "c sl mpr=80.0" (this will take 2 minutes).
3. Then issue "c wca lock=(80.0,6)"
4. On the object explorer running on crc-01, under FLOOG->Control/ALMA01->SetUserFrequency() to 101.03375e9. Repeat for ALMA02.
5. When finished observing, tune the slave laser back to 85.8 GHz with "c sl mpr=85.8"
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| First interferometric spectra
| First Orion spectrum in TDM mode (Todd and Robert -- January 19, 2008)
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| Orion spectrum in TFB mode (Al and Remy -- April 8, 2008)
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| Pointing model behavior at high elevations
| ATF Jan 2008 journal entry
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| Az, El, great circle angle vs. commanded elevation showing the elevation software limit of 88.96 deg.
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| Az,El vs El and time showing elevation software limit of 88.96 deg, and good agreement between model (red) and commanded values (blue)
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| Poor tracking on AEC and Vertex antennas
| email message describing the plots
| AEC plots
Vertex plots
|
