Tech Developments 2003


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Technical Developments for 2003/2004


 

Dual-channel, SSB SIS receivers: 0.8, 1.3 and 2 mm for the SMT:

Several changes are being made to the receivers and associated systems during this time period.

The JT system which incorporates 6 mixers to cover the bands from 130 GHz to 300 GHz has been installed on the telescope for engineering tests. It has since been returned to the lab to continue development. The receiver will be installed with the low frequency pair fitted. The high frequency pairs will be retrofitted as various parts of the optics become available.
A dual channel, single sideband 0.8 mm receiver is under construction, which has similar features to those of the 1-2 mm system.  This system is in a separate dewar, which has additional space available for a set of 490 and 660 GHz mixers. A CTI 1020 refrigerator has already been purchased and the JT system has been built. This project will continue throughout the year.
A cryogenically cooled cold load has been designed and partly built. By utilizing a closed cycle refrigerator, the temperature of the cold load should be stable and can be easily measured. The load will be installed in the tertiary room on a fixed mount. When the cold load is selected, a shaped mirror will drive mechanically into the receiver beam at the vertex (similar to the operation of the existing hot load). The optics will be completed during the next few months and the installation should be completed and tested during the next summer shutdown.
 

                  

        Fig 1                Fig 2                    Fig 3                Fig 4

Figure 1:  Four of the six inserts for the new 1-2 mm SIS receiver (130 - 300 GHz) for the SMT.  Two inserts are required for each waveguide band for dual polarization

Figure 2:  The inside of the 1-2mm receiver showing 2 of the inserts attached to the “spider”, which is connected to the 4-K station.

 

          

    Fig 5                    Fig 6                    Fig7

Figure 5:  The part of the optics of the 1-2mm receiver showing several of the polarizing grids and the Martin-Puplett interferometer used for image rejection.


 

 IF Upgrades for the SMT:

The IF section of the telescope is being upgraded to support receivers with an IF frequency in the 4-6 GHz band. This high instantaneous IF bandwidth
will be available in the new receivers (the JT system and Desert Star). An Agilent synthesizer with excellent phase noise specifications (as shown by the success of the VLBI experiments) has already been purchased and integrated into the system. The automated broadband IF routing switch box has recently been completed and some further setup is required. This makes it possible to inject test tones and to apply broadband comb sources to the backends from the operators’ console. The correct IF is automatically selected when the operator selects a receiver.
 


 

 2048 Channel 1 MHz Filterbank under construction for the SMT.

A new filterbank spectrometer for the SMT is currently under construction. This instrument will have at total of 2048 channels of 1 MHz resolution, steerable in groups of 256 channels to any one of 8 receiver inputs and to any segment of the 4-6 GHz IF. The instrument uses modern surface-mount technology and is built on Euro cards. Calibration and IF leveling are automatic. When complete, the instrument will occupy two standard 19 inch racks.  The first 512 channels of the bank should be at the telescope by the end of 2004.

          

    Fig 1                    Fig 2                Fig 3                    Fig 4

Figure 1:  Prototype filterbank card for the new filter bank system showing 16 channels with its output amplification stage.  The imprint at the top will hold an additional 16 filter channels when completed. 


 

SMT Control System Upgrade.

Background.

In the spring of 2001 the staff of the ARO began the task of replacing the outdated control system of the HHT.  The old antenna control system was based on a single VAX computer interfaced to the antenna control hardware and spectral line backends mainly through CAMAC electronics packages.  The CAMAC electronics was obsolete, difficult to maintain, and was increasingly unreliable.  The VAX control computer was also dated, but couldn't be replaced since the CAMAC electronics interface requires a Q-bus machine (which is no longer made). 

When the old control system was first written, the computing power in microprocessors was very limited.  So instead of doing all time-critical computing in a dedicated microprocessor, only the antenna servo loop was done in the microprocessor.  The other time critical calculations were done in programs running on the VAX, which in the old design, had to monitor and update the microprocessor commands four times a second.

Another issue was the VMS operating system.  Since it was no longer very popular, many of the current data analysis software packages either aren't available under VMS or a VMS implementation of their latest versions was not available.  Thus, often the data analysis was either done with older version of these packages or the data had to be moved to a UNIX platform for analysis.

Goals.

The primary goal was to completely replace the old CAMAC/VAX control system with modern hardware and utilize State of the Art operating system technology. We modeled the new control system after the one developed by the National Radio Astronomy Observatory for use on the Kitt Peak 12 Meter Radio Telescope. Most critical systems are Linux base x86 hardware. This allows us the most flexibility in hardware choices and prevents us from getting 'locked' into one vendor’s wares. The following is a brief description of the current 12 Meter system:

The 12 Meter control system, created in 1990 and highly refine over the years, is one of the most modern of its kind. It is a highly distributed network based control system. Consisting of multiple processors running a variety of operating systems from Solaris to Linux, it represents the state of the art in heterogeneous control system design.  Observations are carried out in a most efficient manner. Be it simple point and integrate or highly demanding, fast On-The-Fly observing. All functions of the system control, including remote observing, are presented to the operator and observer through interactive, intuitive graphical user interfaces.

It was our goal to apply the same control system philosophy to the HHT.

 

Control System Design Features.

Graphical Nature.

     Instead of a command line control interface, the new control system is completely graphical in nature. All operator and observer interfaces are point and click. In addition all system and sub-system parameters are displayed via graphs and plots.

Remote Observing.   -- Remote Observing Manual.

Purpose.

The new control system had remote observing built in from the start. It is modeled after the highly evolved 12 Meter remote observing package. The following is a description of the 12 Meter remote system which is fully applicable to the current SMT remote package:

The KP12m telescope has made significant advances in the development and implementation of remote observing. An astronomer can log-on to the telescope control system from virtually anywhere in the world and set up a software package in a matter of seconds that entirely mimics the system at the telescope. The astronomer views the data on-line in real time as if they were at the site. This capability is augmented by highly skilled telescope technicians on the site who perform all necessary local functions for the observer, such as tuning the receiver to a new frequency. The observer interacts with the site technician via a "chat window". Even a laptop computer can be used for remote observing. A unique software/hardware package has been developed over the years for this purpose, and has been thoroughly tested by observers from all over the world who use these remote capabilities. Moreover, it allows for extreme flexibility in telescope schedule, and is perfect for long-term monitoring program and/or sudden developments, such as the appearance of a new comet.

Remote Debugging. One of the more useful features of a highly evolved remote observing package is in it's utilization during remote debugging. Because of the 'you are there' nature of this package, technicians and engineers are able to diagnose most problems faster and prevent the majority of unnecessary trips to the site. Thus, improving telescope efficiency

Student training. Student astronomers can be trained in mm observing by utilizing the SMT remote observing package. Without the expense of travel, astronomy professors can train a multiple number students in all aspects of radio astronomy observing with out leaving their home institution. Veteran astronomers can observe at the site while their students look in from back home and vice versa.

Remote Collaborators. Large collaborative projects can be carried out with only a few if any astronomers actually traveling to the site while all others can observe remotely. Each remote observer can share different times to oversee the science while the others are teaching,  sleeping or working on other projects.

Remote Monitoring. Another feature of remote observing is utilizing it for remote monitoring. By setting up a permanent remote session in the downtown offices, the Tucson staff can 'look in' on the current observing and thereby oversee the facility.  More then once a situation has been discovered remotely on the 12 Meter and corrected by the Tucson engineers.

Parallel Processing.

Because the new control system is of a distributed design, the processing power is magnified many times over. This also lends itself to parallel processing. Many different tasks are carried out simultaneously.  This design allows the backend computers to concentrate strictly on the process of data taking. Tasks such as graphical displays, file servers and on-line analysis are handled by separate processes in other computers. So for instance, all the while the file server is writing the just completed scan to disk, the on-line analysis is reducing it and the graphics engine is displaying the results, the backend is already taking the next scan. In fact, while observing, the backend never stops.

Modern Independent Hardware.

One of the problems with the old system was its complete dependents on proprietary hardware and operating systems that are difficult to maintain and in most cases no longer manufactured. Our goal was to design the new system around off the shelf hardware that is currently manufactured by many different vendors.  The operating systems are of open system design.

By the very nature of our distributed design, hardware can be selected for each specific task. By utilizing generic off the shelf hardware we are insuring ourselves future expandability and modernization. Due to our modular design, a single functional peace of hardware can be upgraded without affecting the other systems.

Efficiency.

There was much inefficiency in the old system.  Spectral line beam switching had an inherent inefficiency that ranged from 25 to 50%. This was primarily due to the non synchronized nature of the hardware. Also large periods of dead time existed at the beginning of and in between scans. Both of these and other minor inefficiencies were addressed during the upgrade. We have achieved a 2X improvement.

Data Rates.

In the old SMT control system, data could only be dumped from the backends at a rate of once every two seconds. This limited the speed at which a On-The-Fly map could be acquired. The new control system dumps it's data at the rate of 10 times/second. This will allows for OTF maps of the same size to be taken at 1/20 the time.

Capability with 12 Meter.

Because the SMT control system looks and behaves much the same as the 12 Meter system, several advantages can be realized:

Observer Familiarity. Observers will see the same computer interfaces both on site and remotely. This reduces the observer's learning time and simplifies observing manuals and procedures.

Operator Familiarity. Operators also see the same interface at both sites. This too simplifies operator training and facilitate the use of operators working both sites. New operators can be trained on the 12 Meter and then moved to the SMT with minimum retraining.

Eases Troubleshooting. Both sites utilizing essentially the same control system, will simplify diagnosing problems as technicians and programmers need only know one system

Results

The new control system has been in place and operational since November 2002 and since then has undergone steady improvements. All spectral line back ends have been implemented and observing procedures have been finalized. We continue working to improve observing efficiency. Also, we are working on more graphical user interfaces to afford the operators and observers more information in real time to allow informed, fast decision making in regards to their observational project. See figure 1 in the section on OTF mapping for an example of fast mapping at the HHT using the new control system.

 



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Last updated: 11/08/11.