| dc.description.abstract | 5.1 Review
As shown in the previous chapters through analytical, design, and experimental studies, the PC?based DAS is a very useful building block in radio interferometry. This has enabled the development of a PC?based radio interferometer with the following important characteristics:
a) Standardisation in data structure
b) Flexibility of on?line data manipulation
c) Easy transportability of unprocessed data between different observatories
d) Facility for real?time interference rejection
e) Convenient initial off?line data processing
f) Low cost in system implementation
Thus, the use of PCs in radio interferometers has proved to be an elegant and attractive approach, bringing considerable standardisation, convenience, and flexibility at low cost and high reliability. This has been described in detail in the thesis.
The main contributions of the thesis are:
a) A detailed analytical study of a DAS
b) Design and development of a PC?based DAS
c) Experimental verification of the DAS by simulation
d) Overall system integration to realise a PC?based radio interferometer
e) Conducting initial astronomical observations
These studies and investigations have indicated that a PC?based system is attractive in several respects for a small radio interferometer. The preliminary tests conducted so far on astronomical observations show that this interferometer can provide useful data and results in an economical and elegant manner. Considering the present trends in PCs—i.e., availability of more computing power at higher and higher speeds at steadily decreasing costs—it is likely that this approach will become more popular and an accepted standard practice in future instrumentation for radio?astronomical applications of similar scale.
5.2 Scope for Future Work
Apart from the on?line data acquisition and storage functions, and the off?line analysis of this data, the PC?based DAS may be extended for use in the following applications:
a) On?line data analysis
b) General?purpose DAS
These features are expected to enhance the operation of future radio interferometers.
5.2.1 On?line Analysis
The DAS in its present form can be put to greater use, especially in the field of data analysis. This is possible because the host machine is essentially a PC with inherent flexibility and expandability, unlike conventional approaches where a dedicated hardware system is usually employed for this purpose. The extra computing power required for on?line analysis appears feasible when using a PC?AT or more advanced PCs, as an alternative to the PC?XT used here, without any changes in the DAS add?on card.
5.2.2 General?Purpose DAS
The data acquisition add?on card has the following specifications:
a) Sampling frequency: 30 samples per second (maximum in single?channel mode)
b) Input signal range: 1 mV – 1 V
c) Dynamic range of ADC: 1:4000
These specifications are adequate for a DAS in most radio?interferometry applications. Hence, this PC?based DAS is suitable as a general?purpose data?acquisition and storage system. Since the acquired data is stored on the hard disk of the same PC, the system can be easily adapted for a wide variety of applications by simply changing the operating software. As analysis software is usually application?specific, it can be developed easily on the same user?friendly host PC.
In interferometers, as the baselines become longer, the number of interference fringes per second increases. This would require higher sampling rates. The system can be made capable of handling higher sampling rates by employing superior ADCs, such as the successive?approximation type. Such a system would become a standard PC?based unit not only for radio astronomy but also as a general?purpose DAS for other applications.
To store a continuous stream of incoming data, it may become necessary to employ on?board memory on the add?on card itself, as the digital data rates would be much higher than in the current system. In such cases, it would also be necessary to configure this on?board memory as a dual?bank switched type, to prevent loss of data while transferring it to secondary storage devices such as the Winchester disk or MTU, which are relatively slow in operation. | |
