Tid_scan

class Data_Reduction.DSN.Tid_data.Tid_scan(dss, numbers)

Bases: object

Make a Tidbinbilla spectral scan object

This covers spectra taken with the HP9825 controller. The header variables are all flots and the assigments are:

01   file number of next scan to be stored
02   integration time (secs)
03   year (i.e. 1776)
04   day of year
05   UT (hrs) for the start of the scan
06   current R.A. (hrs)
07   current Decl. (deg)
08   R.A. 1950 (hrs)
09   Decl. 1950 (deg)
10   Vlsr (km/s)
11   Longitude (deg)
12   Latitude (deg)
13   doppler factor
14   L.S.T. (hrs) for the end of the scan
15   line rest freq (MHz)
16   synthesizer (MHz)
17   signal I.F. (MHz)
18   phase-lock I.F. (MHz)
19   sideband number
20   calibration temp (K)
21   time per on or off source integration (sec)
22   observing mode number
  =1   TEST mode
            data                      -> C[] -> tape
  =2   POSITION SWITCHING (front end not switching: (-) beam)
            off source noise diode cal data -> K[]
            off source                      -> C[]
            on source                       -> D[]
                 Tcal*(D[]-C[])/(K[]-C[]) -> tape
  =3   LOAD SWITCHING (switching between (-) beam and load)
       TOTAL POWER (not switching: (-) beam (+) ref beam)
            off source                 -> C[]
            on source                 -> D[]
                 Tload*(D[]/C[]-1)    -> tape
                 Tsys*(D[]/C[]-1)     -> tape
  =4   CHOPPING (symmetrical switching between two horns)
            noise diode cal in (-) beam   -> K[]
            source in (+) beam            -> C[]
            source in (-) beam            -> D[]
                 0.5*Tcal*(D[]-C[])/K[]   -> tape
  =5   BEAM SWITCHING (switching between two horns)
            cal in (-) beam           -> K[]
            source in (-) beam        -> C[]
                 Tcal*C[]/K[]         -> tape
  =6   FREQUENCY SWITCHING (source in (-) beam)
            cal  with r35 ch. offset        -> K[]
            data with r35 ch. offset        -> C[]
            data with 0   ch. offset        -> D[]
                 Tcal*(D[]-C[])/(K[]-C[])   -> tape
  =21  POSITION SWITCHING (front end not switching: (-) beam)
            off source noise diode switched -> K[]
            off source                    -> C[]
            on source                   -> D[]
                 Tcal*(D[]-C[])/K[]      -> tape
  =99  Y-Factor measured with power meter
23   number of channels of center frequency offset
24   bandwidth (MHz)
25   SDS total counts/sec
26   SDS d.c. counts/sec
27   system temperature (K)
28   if 1, use comet velocity formula
29   azimuth pointing offset
30   elevation pointing offset
31   H.A. reference offset
32   dec. reference offset
33   H.A. source offset
34   dec. source offset
35   channel offset for frequency switching
36   synthesizer harmonic
38-49 source name in ASCII codes
50   number of channels (64: Y-factor, 256: SDS or 16384: DAVOS)
51   DSS
52   calibration time
53   test tone frequency offset (relative to receiver freq)
54   test tone level (dBm)

Notes

Receiver configurations

1. A K-band maser was installed in 1981. It had one linear polarization. The receiver was based on a phase-lock Gunn of an OVRO down-converting to S-band design. The back-end was a 256 channel SpectraData Fourier Transform Spectrometer built by George Morris.

2. In early 1988 a Ku-band HEMT LNA front end was installed. It used an HP synthesizer as a first LO, down-converting to S-band.

3. Around 1995 an 18-26 GHz HEMT was installed. Also, at some point, SpectraData was replaced with the DAVOS spectrometer.

Frequency calculations

1. RESTFREQ is the frequency of interest, usually a line frequency, in the rest frame of the source, in Hz

2. obs_freq is the frequency in the rest frame of the observer where this feature of interest appears. It is computed from the Doppler factor.

3. exp_freq is the frequency in the rest frame of the observer where this feature of interest should appear, calculated as an offset from the receiver frequency. We expect exp_freq = obs_freq.

Source name encoding

In 1989, the convention was to put the source name on the first line of the scan block, after the scan number.

1991/123 the header numbers[37:49] were reserved for source name encoding but filled with the negative of the index number.

1991/174-194,1992/144-1145 zero-filled again.

1992/165 source name encoding started but it was wrong, mostly:

['11 09 45.', '11 09 45.', '17 42 29.3', '17 42 29.3',....
 '17 42 29.3', 'G1.6 meth peak', 'G1.6 meth peak', 'G1.6 meth peak',
 '17 42 29.3',.... '17 42 29.3', '1', '1', '1']

That was sorted out on 1992/236.

1995/066 the source name encoding in numbers[37:49] was erroneously broken up by the number of spectrometer channels in numbers[45]. Also, the number encoded was ‘256’ whereas the DAVOS spectrometer (16384 channels) was already being used.

On 1995/090, number of scans moved to numbers[49]

If a source name cannot be extracted, then the coordinates are used to try to find the source name.

Methods Summary

get_scan_data(dss, numbers)	Get data for a scan.
print_header()	Print the header of a Tid_scan instance

Methods Documentation

get_scan_data(dss, numbers)

Get data for a scan.

This sets values in self.header and self.data

:param dss : DSN station number :type dss : int

:param numbers : scan data :type numbers : float

Returns

None

print_header()

Print the header of a Tid_scan instance

Returns

None