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A Report on the Spectrometer Tests of September 10/11, 2002
Configuration: 4N2-6A-12-9; L Band

Summary

The GBT spectrometer was used in five configurations during the night of September 10/11, 2002. This report summarizes what was observed in the third configuration.

The results are satisfactory, and it is recommended that this correlator configuration be released for general use at L Band.

Analysis

The data are in the GBT data base as /home/gbtdata/TSPECTEST_05. The data were filled into an area on EUCLID:
/export/home/euclid/scratch/dhogg/ and are in file:
TSPECTEST_05_SPECTROMETER_A

Configuration 3. 4N2-6A-12-9
L Band, at 1429 MHz; 12.5 MHz bandwidth; 9-level sampling.

Observations were made of the hydrogen line in the galaxy UA93o chosen from the Fisher GBT HI Galaxy Survey, Scans #59 to #68. 

Scans #60,#62, #64, #66, and #68 are all comparable, and are all
good scans. We have averaged them to get a best estimate of
the HI spectrum. Figure 1 (ttday5#60pla.ps) shows the spectrum for
each receiver averaged over all scans, with intensity as a function
of pixel number. Figure 2 (ttday5#60plb.ps) shows intensity as a function
of frequency. 





For one 300 second observation in one receiver, with a
channel width of 380Hz, and a system temperature of 20 K, we expect
the rms to be 59 mK. The observed values are shown in the following table.

Effective                  RMS, in mK                     Ratio
Int. Time           Expected     RX1    RX2    Both        O/E
   150                59.1      55.3   53.6               0.92
   300                41.8                     38.6       0.92
   750                26.4      24.6   23.9               0.92
  1500                18.7                     17.1       0.91

The receivers are of comparable sensitivity. The observed rms is
about 8% less than the expected value. The rms decreases with
increasing integration time exactly as expected.

Figure 3 shows the graph of RMS as a function of integration time.
The solid line is the expected rms, and the triangles are the
observed values.


The final spectrum obtained by integrating all data is given in
Figure 4 (ttday5#60ava.ps), which shows intensity as a function of
barycentric radial velocity. The figure has been cropped to give
a display similar to that in the Fisher catalog. 


Figure 4 shows the profile of galaxy UA93o from the Fisher catalog.


The properties
of the profile are compared in the following table. We use the
average of the two channels for each IF, and we convert from
antenna temperature to flux density using the conversion factor
found in early August by R. Maddalena, 1 Jy = 1.91 K.

Quantity                     Fisher          This Test

Maximum in profile (Jy)                         0.45

Peak Intensity     (Jy)       0.38              0.42

Line Width @ 20%   (km/s)     194.7             195.1

Systemic Velocity  (km/s)     717.7             717.8

Flux Integral   (Jy km/s)     57.30             60.15

The velocity parameters are in excellent agreement. The peak
intensity and the flux integral are slightly higher in the
test than in the Fisher profile, by 11% and 5% respectively.
It should be noted that the peak intensity in the test is an
estimate, and may not be at the same point in the profile
as the Fisher value.

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