AMiBA Engineering Telecon Minutes

11, July, 2002

Participants:	Australia:	M. Kesteven, W. Warwick
	USA:	B. Martin, D. Kubo, J. Peterson
	Taiwan:	P. Ho, H. Wang, T.H. Chu, T.D. Chiueh, M.T. Chen,
		C.T. Li, Y.J. Hwang, H.M. Jiang, W. Ho, T. Huang, C.C. Han,
		C.J. Ma, K.Y. Lin, T. Wang, P. Shaw

Summary

Receiver:

Mingtang updates the status of prototype receiver:

1. One awkward feature on the output spectrums from all receivers is the steep gain slope in the lower frequency, roughly below 5 GHz, some out to 10 GHz. Eugene spent some time to investigate possible cause. In the end we summarize that is an accumulative effect from the components in signal chain, plus the spectrum analyzer gain variation. Nothing we can do about it, except put in an equalizer. Conclusion is that in the future we have to be careful in choosing components for a single receiver channel. Thus, test data of individual component is important in this aspect.

2. We started stability test. The first result from RX1-IF1 has been circulated. Fluctuation, presumably 1/f, is observed. Receiver temperature is observed to drift slowly, 1% over 12 hours on LNA. No obvious correlation between temperature and output power is observed.

3. Desperately looking for a set of filters to cover AMiBA band. Most important so far is the 2GHz HPF. Derek is helping on this.

4. The activity in Chu & Co. Work on equalizer v0.2 is started. The new one is aiming to provide better matching, as well as broom away signal below 2GHz. (That would be wonderful) It will come in a smaller size, too, to fit in the IF box.

5. Two receiver electronic enclosures are shipped to Hilo this week. Ted Huang and Tashun Wei will be in Hilo the week of 7/22. Installation of these enclosures is one of their tasks during their stay in Hilo.

6. Ma Cheng-Jiun is helping on ordering two more prototype feed horns from Thomas Keating in UK.

7. We have started part acquisition for the third receiver. Hopefully before Oct. we would have one more receiver running.

8. There are still some noise in the correlator data taking area, C.T. will do more measurements on the correlator and mixer in a week or two.

LO/IF

As for the LO new version, Prof. Chu said that they will not use the same components as for the prototype, since they are too rigid to assemble. And he found the cable which made by themselves is quite good, the loss measured for a 10m long cable is less than 1 dB.

And for the IF, he realized the return loss of the equalizer is too high, now they are working on a new design. In addition, they will add a capacitor in series with equalizer to cut off the low frequency signal to reduce the loss.

Correlator:

1. C.T. made some measurements on the correlator with the battery biased, he found a huge noise came out from the un-proper connection of power supply box and correlator box. So that he will re-arrange the connection and measure SNR again shortly.

2. Derek is working on ordering the components for 7 elements.

3. Due to the lack responses of Rapadas’ biased mixer at the low end, Jeff suggested him to change its circuit. We’d better wait for a while to see its final test result before decide which approach should go with for 4 lag correlator; biased or non-biased mixer.

Platform:

1. VA is studying a platform and has started with a design of a 300 mm thick open box sandwich, similar to the ALMA dish design. Deformations under gravity loads are much higher than the specs. The current structure is 800 mm thick, weighs 890 kg and still does not meet specs. The surface accuracy is about 100 microns when optimized at an angle between 30 and 90 degrees of elevation, plus another 10 to 20 microns for operational wind loads. VA is using the best fiber on the market, also the most expensive. The height of the platform is a problem of concern for wind loads. VA asked us to reconsider these issues in the coming days and revise the specifications if necessary.

2. Bob would like to review the specification in the next week, he asked everybody to think about the weight of the elements we will put on the platform.

Far field range measurement:

C.J. Ma and K.Y. Lin have made some measurements on the 30cm dish and circulate its result around in yesterday,

Action items:

1. All/ We need to review the specification of platform to figure out a real accurate guess of the weight which putting on the platform next week.

2. All/ Bob raised a power distribution proposal to everybody to look; we will get back to discuss it next week.

3.Jeff/ As for ordering two 60cm dishes for prototype testing, Jeff will come up with a proposal and cost estimate, and circulate to everybody to look shortly.

4. Bob/ Bob will talk to Huei further details on the collaboration issue with JPL next week when he is Taipei.

Next telecom: Thursday, July 18, 8:30AM Taipei time.