3mm amplitude test
description
Transcript of 3mm amplitude test
3mm amplitude test
by
Cheng-Jiun Ma
Observation
• Source : Orion SiO
• Frequency: 86.243GHz
• 256 channels within 64MHz bandwidth
• Ant 3 & Ant 4
• no Tsys correction
• fixed attenuations
-180
-130
-80
-30
0 20 40 60 80 100 120 140
time (10sec)
phas
e (d
egre
e)
OrionSiO
0
5
10
15
0 20 40 60 80 100 120 140time (10 sec)
amp
off source
Cross correlation of ant 3 and ant 4
Possible reason
• System temperature fluctuation
• Variation of gain in receivers/antenna
• Inteferometry phase fluctuation
• Pointing accuracy
antennae 4
570
580
590
600
610
620
630
640
650
0 20 40 60 80 100 120 140
time
channel 110-140channel 70-100channel 150-180
antennae 3
575
580
585
590
595
600
605
0 20 40 60 80 100 120 140
time
channel 110-140channel 70-100channel 150-180
central band off source
central band on source
autocorrelation
0100200300400500600700800
0 50 100 150 200 250 300
channel
amp
autocorrelation signal and noise
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 20 40 60 80 100
time
amp
normalized 34aa
ant3*ant4
Compare the product of autocorrelation amplitude of ant3 & ant4 with the cross correlation amplitude.
The amplitude variation comes from the single dishes, and not because of the inteferometry phase.
Second observation
• High time resolution (0.3 sec)
• cross correlation only
• 32 channels with 128MHz bandwidth
OrionSiO
01234567
300 350 400 450 500
time(0.3 sec)
amp
-180
-120
-60
0
300 350 400 450 500
time (0.3 sec)
phas
e (d
egre
e)
off source
0
2
4
6
700 750 800 850 900
time (0.3 sec)
amp
Third observation
• after adjust the pointing
• do bore sight track and ½ power track alternatively
• 10 sec averaging
0
2
4
6
8
10
12
43000 43500 44000 44500 45000 45500 46000 46500
time (sec)
amp
bore sight
1/2 power
off source
-180
-120
-60
0
60
120
180
43000 43500 44000 44500 45000 45500 46000 46500
time (sec)
phas
e (d
egre
e)
bore sight
1/2 power
ca34Bore sight ½ power
1 2 3 1 2
AVG 8.90 7.57 6.71 4.23 4.04
N_RMS 0.07 0.06 0.07 0.22 0.14
The rms of the normalized amplitude is higher when the source is at 1/2 power.
Observation on 3.14
• Source: Orion SiO
• Frequency: 86.243GHz
• With 32 channel in 128MHz band
• Ant 4 autocorrelation only
orionsio 1/2 power 2
0
1
2
3
36300 36320 36340 36360 36380 36400
time (s)
normalized amplitude v.s. time
orionsio bore sight 1
0.7
0.9
1.1
1.3
1.5
1.7
33800 33820 33840 33860 33880 33900
time(s)
orionsio 1/2 power 1
0.7
0.9
1.1
1.3
1.5
1.7
34800 34820 34840 34860 34880 34900
time(s)
orionsio bore sight 2
0
0.5
1
1.5
35650 35670 35690 35710 35730 35750
time (s)
bore sight 1
0
0.02
0.04
0.06
0.08
0.1
33800 34000 34200 34400
time (s)
rms
bore sight 2
0
0.05
0.1
0.15
0.2
35400 35600 35800 36000
time (s)
rms
1/2 power 1
0
0.1
0.2
0.3
0.4
34700 34900 35100 35300
time (s)
rms
1/2 power 2
0
0.2
0.4
0.6
0.8
35900 36100 36300 36500
time (s)
rms
rms of normalized amplitude v.s. time
aa44 3.14 off sourcebore sight ½ power
1 2 1 2
avg 551.18 14.05 11.70 6.61 5.83
n_rms 0.08 0.14 0.30 0.43
Autocorrelation data
The autocorrelation amplitude rms is also higher
when source is at half-power
The main reason for the variation
System temperatureThe variance of the off-source-channel amplitude is much smaller than that of the on-source amplitude.
gain
receiver
antennaeThe variance of the amplitude of the source on the peak is different from that of the source on the half power , which should not happen if the variation is caused by the antennae gain.
phase1.The product of the autocorrelation data is highly consistent with the cross correlation data.
2 .Sometimes, the phase is quite stable but the amplitude still oscillates a lot.
pointing
tracking error
1.The error showed on the ACC system is not larger than 3 arcsec.
2.We are going to check this by mounting the optical telescope on the antennae.
drift caused by the atmosphere
There is a small time scale, about 10 seconds, for variation of the autocorrelation amplitude.
The spatial scale of the random motion is about 10 arcsec.