K-band FPGA Single Pixel Test Report for 2008 December 28
These single pixel tests compared the (K1) performance with the current GBT K-band receiver (K0). The observations were made under reasonable good weather conditions, but there was some humidity, which makes the direct comparison more difficult. We also searched IF spurs that might have been generated by the second type of down converter unit.
The summary of our findings are:
- The system temperature performance of the K0 and K1 systems are similar.
- No IF spurs were found in the K1 spectra obtained. Due to a lack of time, only part of the band was scanned for IF spurs.
K0 and K1 System Temperature comparisions
We observed source 3C123 with the K0 feed at 19, 23, 25 and 21 GHz (in that order), to get representative measures of the system temperature across the band. We also observed the same source at 25, 19, 21 and 23 GHz with the K1 feed. Below the system temperatures and source peak heights are listed in observing order
The K1 T
cal temperatures were measured in the lab. Selected values are listed in the following table. These cal values are used to scale the K1 system temperatures.
Freq. LCP RCP
GHz K K
19 6.20 5.36
21 4.13 4.14
23 5.57 5.39
25 7.30 7.82
The K1 cal values are used to convert the T
sys and T
source values (measured with Astrid assuming T
cal = 1) to Kelvin Units. In the tables below, the T
sys values are measured from the noise-diode count (Counts
on, Counts
off) values. The source sntenna temperature values are deduced from measurements as follows:
T
source = T
sys_off*(Counts
On-Counts
Off)/Counts
Off Next the K0 system and source antenna temperatures are logged:
Scans Type Feed Center LCP RCP
Freq Tsys Peak Tsys Peak
GHz K K K K
8-11 Peak K0 25 52.2 2.55 53.1 3.35
12 Focus K0 25 52.1 2.44 53.1 3.17
13-16 Peak K0 23 60.3 3.36 61.5 3.48
17 Focus K0 23 60.3 3.29 61.4 3.46
18-21 Peak K0 19 37.8 4.78 39.0 5.16
22 Focus K0 19 37.8 4.72 39.0 5.10
After the observations with the K0 feed were recorded, we switched to the single pixel and made peak and focus observations on the same source, at the same frequencies.
LCP RCP LCP RCP
Tsys Tpeak TSys Tpeak Tsys Tpeak Tsys Tpeak
counts counts counts counts K K K K
31 Focus k1 25 7.30 0.458 8.53 0.436 53.3 3.34 66.7 3.41
32-35 Peak K1 25 7.46 0.314 8.69 0.306 54.5 2.29 68.0 2.39
37-40 Peak K1 19 7.72 0.903 8.26 0.860 47.9 5.60 44.3 4.61
41 Focus K1 19 7.76 0.931 8.30 0.871 48.1 5.77 44.5 4.67
44-47 Peak K1 21 13.5 0.950 13.63 0.858 55.7 3.92 56.4 3.55
48 Focus K1 21 13.45 0.950 13.56 0.852 55.5 3.92 56.1 3.53
54-57 Peak K1 23 12.18 0.596 12.17 0.542 67.8 3.32 65.6 2.92
58 Focus K1 23 12.22 0.560 12.20 0.510 68.1 3.11 65.8 2.75
We needed observations at 23 GHz with K0, in order to compare the observations and see how much the sky temperature had changed during the tests. We switched back to K0 for a short period. The final test was a repeat of the K1 observation at 25 GHz.
59-62 Peak K0 23 69.5 3.47 70.9 3.62
63 Focus K0 23 70.0 3.52 71.4 3.69
69-72 Peak K0 21 59.5 3.85 66.8 4.53
73 Focus K0 21 60.2 3.72 67.7 4.40
LCP RCP LCP RCP
Tsys Tpeak TSys Tpeak Tsys Tpeak Tsys Tpeak
counts counts counts counts K K K K
74-77 Peak K1 25 8.42 0.275 9.60 0.262 61.5 2.01 75.1 2.05
78 Focus K1 25 8.51 0.316 9.69 0.277 62.1 2.31 75.8 2.17
These observations show a number of important points:
- The system temperature values for K0 and K1 are similar.
- The pair of 23 GHz observations with K0 suggests the sky brightness temperature increased by 10 K during the observations.
- The pair of 25 GHz observations with K1 suggests the sky brightness temperature increased by 9 K during the observations.
Scan for IF spurs: 3C123 Spectra
The second part of our test was a search for IF spurs that could have been generated by the down conversion units.
The check was made by stepping across the spectral band from 18 to 22.4 GHz, performing 2 minute On-source, Off source
observations. The results of these observations are shown in the figures below. There data are calibrated
using the laboratory measurements of the noise source values. The Left Circular polarization is to the left
and Right Circular Polarization is to the right.
K1 L-polarization Tsys_off (On-Off)/Off on 3C123: |
K1 R-polarization Tsys_off(On-Off)/Off on 3C123: |
|
|
We would expect the T
antenna values for 3C123 to be monotonically decreasing as a function
of observing center frequency. The Ott et al (A.A.) model for the source flux density (Jy) is shown
in the figure below.
|
Plot of 3C123 Flux density vs frequency
|
Observing log
Start Stop Source Procedure # RA-2000 Dec-2000 # Sky Freq
Scan can Name (hms) (d'") Data (MHz)
====== /home/gbtdata/T_KFPA_08DEC28 ==== T_KFPA_08DEC28 ==== Glen Langston
1 4 3c123 Peak 4 4h37m04 29d40'15 576 24999 DCR 2008_12_28_05:09:10
5 5 3c123 FocusSubreflec 1 4h37m04 29d40'15 294 24999 DCR 2008_12_28_05:11:38
6 6 3c123 Tip 1 3h41m43 10d02'02 1494 24999 DCR 2008_12_28_05:17:20
7 7 3c123 Tip 1 3h48m03 10d00'07 1494 24999 DCR 2008_12_28_05:23:48
8 11 3c123 Peak 4 4h37m04 29d40'15 576 24999 DCR 2008_12_28_05:31:16
12 12 3c123 FocusSubreflec 1 4h37m04 29d40'15 294 24999 DCR 2008_12_28_05:33:41
13 16 3c123 Peak 4 4h37m04 29d40'15 576 23000 DCR 2008_12_28_05:35:58
17 17 3c123 FocusSubreflec 1 4h37m04 29d40'15 294 23000 DCR 2008_12_28_05:38:24
18 21 3c123 Peak 4 4h37m04 29d40'15 576 19000 DCR 2008_12_28_05:40:47
22 22 3c123 FocusSubreflec 1 4h37m04 29d40'15 294 19000 DCR 2008_12_28_05:43:12
23 26 3c123 Peak 4 4h37m04 29d40'15 576 25000 DCR 2008_12_28_05:57:20
27 30 3c123 Peak 4 4h37m04 29d40'15 576 25000 DCR 2008_12_28_06:03:58
31 31 3c123 FocusSubreflec 1 4h37m04 29d40'15 294 25000 DCR 2008_12_28_06:08:43
32 35 3c123 Peak 4 4h37m04 29d40'15 576 25000 DCR 2008_12_28_06:13:36
36 36 3c123 FocusSubreflec 1 4h37m04 29d40'15 294 25000 DCR 2008_12_28_06:15:58
37 40 3c123 Peak 4 4h37m04 29d40'15 576 19000 DCR 2008_12_28_06:20:36
41 41 3c123 FocusSubreflec 1 4h37m04 29d40'15 294 19000 DCR 2008_12_28_06:23:00
44 47 3c123 Peak 4 4h37m04 29d40'15 720 21000 DCR 2008_12_28_06:32:30
48 48 3c123 FocusSubreflec 1 4h37m04 29d40'15 144 21000 DCR 2008_12_28_06:34:53
49 52 3c123 Peak 4 4h37m04 29d40'15 576 21000 DCR 2008_12_28_06:39:57
53 53 3c123 FocusSubreflec 1 4h37m04 29d40'15 144 23000 DCR 2008_12_28_06:42:20
54 57 3c123 Peak 4 4h37m04 29d40'15 576 23000 DCR 2008_12_28_06:45:00
58 58 3c123 FocusSubreflec 1 4h37m04 29d40'15 144 23000 DCR 2008_12_28_06:47:23
59 62 3c123 Peak 4 4h37m04 29d40'15 576 23000 DCR 2008_12_28_06:57:47
63 63 3c123 FocusSubreflec 1 4h37m04 29d40'15 144 23000 DCR 2008_12_28_07:00:09
64 67 3c123 Peak 4 4h37m04 29d40'15 576 20999 DCR 2008_12_28_07:02:00
68 68 3c123 FocusSubreflec 1 4h37m04 29d40'15 144 20999 DCR 2008_12_28_07:04:24
69 72 3c123 Peak 4 4h37m04 29d40'15 576 20999 DCR 2008_12_28_07:10:07
73 73 3c123 FocusSubreflec 1 4h37m04 29d40'15 294 20999 DCR 2008_12_28_07:12:30
74 77 3c123 Peak 4 4h37m04 29d40'15 576 25000 DCR 2008_12_28_07:30:12
78 78 3c123 FocusSubreflec 1 4h37m04 29d40'15 294 25000 DCR 2008_12_28_07:32:33
79 82 3c123 Peak 4 4h37m04 29d40'15 576 25000 DCR 2008_12_28_07:35:33
83 83 3c123 FocusSubreflec 1 4h37m04 29d40'15 144 25000 DCR 2008_12_28_07:37:56
84 85 3c123 OnOff 2 4h41m41 29d40'15 12 18000 ACS 2008_12_28_07:50:42
86 87 3c123 OnOff 2 4h41m41 29d40'15 12 18400 ACS 2008_12_28_07:53:47
88 89 3c123 OnOff 2 4h41m41 29d40'15 12 18800 ACS 2008_12_28_07:56:52
90 91 3c123 OnOff 2 4h41m41 29d40'15 12 19200 ACS 2008_12_28_07:59:57
92 93 3c123 OnOff 2 4h41m41 29d40'15 12 19600 ACS 2008_12_28_08:03:00
94 95 3c123 OnOff 2 4h41m41 29d40'15 12 20000 ACS 2008_12_28_08:06:03
96 97 3c123 OnOff 2 4h41m41 29d40'15 12 20400 ACS 2008_12_28_08:09:06
98 99 3c123 OnOff 2 4h41m41 29d40'15 12 20800 ACS 2008_12_28_08:12:11
100 101 3c123 OnOff 2 4h41m41 29d40'15 12 21200 ACS 2008_12_28_08:15:14
102 103 3c123 OnOff 2 4h41m41 29d40'15 12 21600 ACS 2008_12_28_08:18:17
104 105 3c123 OnOff 2 4h41m41 29d40'14 12 22000 ACS 2008_12_28_08:21:21
106 107 3c123 OnOff 2 4h41m41 29d40'15 12 22400 ACS 2008_12_28_08:24:26
--
GlenLangston - 2009-01-16