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.