Dynamic Range Tests

Dynamic Range Tests on Cass A

October 9, 2003
F. Ghigo, NRAO-Green Bank

The feasibility of mapping Cass A and its surroundings was tested by doing scans across Cass A and across sources of about 1-2 Jy to see how linear the response of the system is to a wide range of power levels.

System Components

Front end low-noise amplifiers (LNAs)
IF power range in Prime Focus receivers: 0.1 - 8 v ?
Input to optical drivers: IF power range in IF Rack: 0.1 - 8 v ?
Input to total power detectors in IF rack: 0.1-8v ?
Input to SpectralProcessor: -4 to -34 db ??

Journal of Observations: L-band, September 22, 2003

Scan#	Source	type of scan	levels
5-8	NGC7027	peak/point	normal on NGC7027
9-12	2319+48	peak/point	normal on 2319+48
17	NGC7027	scan 2 deg in Elev.	IF=4v, SP=-4db on CassA
18	NGC7027	scan 2 deg in Azim.	IF=4v, SP=-4db on CassA
19	Cass A	scan 10 deg in Azim.	IF=4v, SP=-4db on CassA
20	Cass A	scan 10 deg in Elev.	IF=4v, SP=-4db on CassA
21	Cass A	scan 10 deg in Elev.	normal off source
22	Cass A	scan 10 deg in Azim.	normal off source
23	NGC7027	scan 2 deg in Azim.	normal off source
24	NGC7027	scan 2 deg in Azim.	normal off source
26	Cass A	scan 2 deg in Azim.	IF=4v, SP=-4db, peak of Cass A
27	NGC7027	scan 2 deg in Azim.	IF=4v, SP=-4db, peak of Cass A
28	Cass A	scan 4 deg in Azim: Freq Switch (SP)	IF=4v, SP=-4db, peak of Cass A
29	Cass A	scan 4 deg in Azim: Freq Switch (SP)	IF=4v, SP=-4db, peak of Cass A
31	Cass A	scan 4 deg in Azim: Freq Switch (ACS)	IF=4v, SP=-4db, peak of Cass A
32	Cass A	scan 4 deg in Azim: Freq Switch (ACS)	normal off source

Note: "normal" levels means power in IF Rack is set to nominal 1v and Spectral Processor to nominal -11db inputs when tracking on the named object.
Setup: Scans 17-27 used 20 MHz bandwidth centered on 1420 MHz for both the continuum(DCR) and Spectral Processor backends. Used 0.2 second noise cal switching; Spectral Processor integration time 2 sec; scanning at 80'/min.
Scans 28,29: use DCR and SP with frequency switching by -2.5 MHz, bandwidth 5 MHz, 1 sec switch period, 2 sec integration.
Scans 31,32: use ACS(Spectrometer) with frequency switching by -2.5 MHz, bandwidth 12.5 MHz, 1 sec switch period, 2 sec integration.

835 MHz, September 22, 2003, bandwidth=20 MHz, DCR and SP.

Scan#	Source	type of scan	levels
34	Cass A	scan 10 deg in Azim	PF=2v, IFRack=4v, SP=-4db Cass A peak
35	Cass A	scan 10 deg in Azim	PF=2v, IFRack=4v, SP=-4db Cass A peak
36	NGC7027	scan 10 deg in Azim	PF=2v, IFRack=4v, SP=-4db Cass A peak
37	NGC7027	scan 10 deg in Azim	PF=2v, IFRack=4v, SP=-4db Cass A peak
38	3C48	scan 10 deg in Azim	PF=2v, IFRack=4v, SP=-4db Cass A peak
40	Cass A	scan 10 deg in Azim	PF=1v, IFRack=3v, SP=-7.6db Cass A peak
41	3C48	scan 10 deg in Azim	PF=1v, IFRack=3v, SP=-7.6db Cass A peak
43	3C48	scan 4 deg in Azim	PF=1v, IFRack=1v, SP=-12db peak of 3C48
45	Cass A	scan 10 deg in Azim	PF=1v, IFRack=1v, SP=-12db peak of 3C48

835 MHz, October 3, 2003, bandwidth=20 MHz, DCR and SP.

Scan#	Source	type of scan	levels
22	2319+48	scan 6 deg in RA, use low cal	normal off source
23	2319+48	scan 6 deg in RA, use high cal	normal off source
26	Cass A	scan 6 deg in RA, use high cal	PF=2v, IF=3v, SP=-4.4db on CassA peak.
27	2319+48	scan 6 deg in RA, use high cal	PF=2v, IF=3v, SP=-4.4db on CassA peak.
28	2319+48	scan 6 deg in DEC, use high cal	PF=2v, IF=3v, SP=-4.4db on CassA peak.
29	Cass A	scan 6 deg in DEC, use high cal	PF=2v, IF=3v, SP=-4.4db on CassA peak.
30	Cass A	scan 6 deg in RA, use high cal	PF=2v, IF=3v, SP=-4.4db on CassA peak.

Note: Using scan rate 180'/min; 0.5 sec noise cal switching; SP integration time 2 sec.