cband wide cal values measured 27apr17
10aug17
Why the cals were remeasured.
The cbw receiver was taken to the antenna test
range (next to the lidar lab) and the cal values were measured using
sky and absorber by Felix et al. on 27apr17.
Results of the measurements:
Values used in the computations:
- Tsky: 6.5K
- Tabsorber:296.3K
We have 2 separate diodes (D1, and D2). These can feed polA
and or polB.
In addition there are attenuators that can be used to go from the
high cal to the low cal values.
The 8 different cal configs:
cal onfig
|
polA
|
polB
|
High cals
|
Hcorcal
|
D1->A
|
D1->B
|
Hcal
|
D1->A
|
D1->B
|
Hxcal
|
D2->A
|
D1->B
|
H90Cal
|
D2->A
|
D2->B
|
Low cals
|
Lcorcal
|
D1->A
|
D1->B
|
Lcal
|
D1->A
|
D2->B
|
Lxcal
|
D2->A
|
D1->B
|
L90Cal
|
D2->A
|
D2->B
|
The Different cal configurations that have the same diode going to
the same Pol, should give the same measurement value (unless
something has changed.. like clouds). eg:
- Hcorcal: D1->polA
- Hcal :D1->polA
plots of ratios of TcalOn -
TcalOff/TcalOff and Tcal (.ps) (.pdf)
- Page 1: (CalOn - CalOff)/CalOff while on
absorber
- top frame: High cal polA
- 2nd frame: high cal polB
- red,black (corcal,xcal) do not track each other.
- 3rd frame: low cal PolA
- the common cal configs to not track very well. Since we
are on absorber, the problem is not clouds..
- bottom frame: low cal PolB
- Page 2: (CalOn - CalOff)/CalOff on sky
- top frame: High cal polA
- 2nd frame: high cal polB
- 3rd frame: low cal PolA
- bottom frame: low cal PolB
- Page 3: Tcal vs freq for high cals:
- top polA
- bottom polB
- the red,black lines do not track very well
- Page 4: Tcal vs freq for low cals.
- top polA
- neither pair of cals track one another
- bottom polB:
- black and red do not track very well.
A fit was then made to each set of Tcal vs freq to extract the
values to use.
Cal configurations that had the same diode feeding the same pol
were averaged prior to fitting.
A a robust fit (1st order polynomial, 3rd order harmonic) was used
to exclude bad points (rfi).
the plots show the fits to the
measured cals (.ps) (.pdf)
- the * show the measured points
- the solid line is the fit.
- Page 1: PolA low cals
- black and green had the same diode,pol config. the fit
splits the difference between them.
- Page 2: PolB low cals
- Page 3: PolA high cals
- Page 4: PolB high cals.
The
Receiver flange temperature was computed from the measurement
(.ps) (.pdf)
Summary:
- The cband wide cals were measured on the hillside
- The high cal values came out around 150 K
- the low cal values were around 10K
- there is up to 6db variation in the cal across the band.
- We will need to put attenuators in the cals to lower the hcal
to around 10 K and the low cal to 1-2 K. We will then have to
remeasure the cals.
- The low cal values that had the same diode feeding the same
pol had a bit of scatter. We may have been close to the
sensitivity limit for them.
- The cals were installed on the telescope on 10aug17.
- An example of the tsys values were:
- Thu Aug 10 16:17:22 2017 az/za lst:
388.2176 1.4999 13:08:21
rcv 13 6000.0 2 3 0 if1 -37.37 -34.05 if2
-41.86 -42.48 cor 0.94 0.92
6 5
13 hcal 155.99
178.27 35.9 39.6
36.0 39.1 36.2
39.3 36.0 39.4
13 hxcal 161.12
164.80 36.6 38.7
36.7 38.1 37.0
38.3 36.7 38.4
13 hcorcal 155.99 164.80
36.7 38.4 36.7
37.9 37.0 38.0
36.7 38.2
13 h90cal 161.12 178.27
36.3 39.8 36.4
39.2 36.6 39.4
36.4 39.6
13 lcal 12.24
14.25 29.4 33.3
29.5 32.8 29.6
32.9 29.4 32.9
13 lxcal 12.23 13.73
30.1 33.5 30.1
33.0 30.2 33.1
30.0 33.1
13 lcorcal 12.24 13.73
30.7 33.6 30.8
33.1 30.9 33.1
30.7 33.2
13 l90cal 12.23 14.25
29.7 34.5 29.7
34.0 29.9 34.0
29.7 34.1
The low cal values are about 7 K below the high cal
values.
processing: x101/cbw/cals/apr17/
home_~phil