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Next: VESPA is operational Up: IRAM Newsletter 54 (December 2002) Previous: New IRAM web site


News from the 30m Telescope

IRAM database for pooled observations

All informations on projects taking part in the pooled observing mode are now stored in our new database system. The database has a web interface which allows to access and modify all information relevant to pooled observing via a web browser.

Projects taking part in the pooled observing mode will have a project account from which PIs can store in the database all instructions necessary to carry out the observations. In turn this account allows the PIs to monitor the progress of their project: each scan taken for a project is displayed together with some basic information such as the date, observing mode and scan duration. Additional comments visible to the PI may be inserted by the observers at the telescope.

To allow a quick look at the data we provide a pipeline NIC reduction for bolometer observations. It allows the user to reduce maps and on/off observations online without downloading the data.

For further data analysis the PIs can download their data via their web browser. Together with the data files, the PIs will retrieve the observing log(s), all macros and catalog files related to the observations and a summary on all scans taken for the project.

Based on the progress in of his project a PI can change the priority of his sources, modify the observing instructions or make comments for observations on individual sources.

All information entered by the PIs is directly accessible to the observers at the telescope. Besides the detailed observing instructions the database provides additional tools for carrying out the observations. Among those are astronomical tools to provide information on visibility of sources and fluxes for all calibrators, as well as project source listings which take into account project priorities and the current weather conditions.

The final decision which sources to observe is made by the pool coordinator at the telescope taking into account visibility, priority and the observing conditions.

A more detailed description of the database will soon be available on our web pages. For more information about the pooled sessions and the database contact


Mobile phone interferences in the filter bank backend

This article demonstrates the disturbance effect that the GSM service for mobile phones produces in the 30-m filter bank backend.

The GSM service uses the frequency bands 890-915 MHz for the uplink (mobile station to base station) and 935-960 MHz for the downlink (base station to mobile station). An interference in the backend spectrum should be produced by the mobile station when transmitting close to the backend electronics.

The following measurements have been done using the 1 MHz filter bank in the broad band configuration, which means 1024 channels of 1 MHz covering the IF range from 86 to 1110 MHz.

Previously, a calibration (CAL COLD procedure) was done with the A230 receiver tuned at 230 GHz. Then the IF cable was disconnected from the receiver and connected to a 50 $\Omega$ load in order to remove the receiver noise from the spectrum. Under these conditions several spectra were taken with a mobile phone transmitting from different distances. Each spectrum consists of two subscans of 3 minutes integration time each. With repetitive conditions results are similar. A summary of all the spectra taken is shown in the following graphics.

In Fig. 2a) shows a reference spectrum when no transmission from a mobile phone is present. Both subscans are similar and the superimposed noise is something intrinsic to the backend and the acquiring data procedure.

In Fig. 2b) a spectrum was taken while a mobile phone was continuously transmitting during the 3 minutes of the first subscan, at a distance of 2 meters of the filter bank electronics inside the backend/computer room. During the second subscan the mobile phone was switched off. Frequencies of the GSM band pass range are indicated, but the corruption extends over the whole 1 GHz band pass frequency.

Figure 2c) finally shows a spectrum taken under similar conditions as the previous one, but with the mobile phone transmitting from the corridor between the backend-computer room and the library, at a distance of approx. 8 meters to the filter bank electronics.

Assuming that

we conclude that a mobile phone should never transmit at a distance shorter than 70 meters to the filter bank electronics when the telescope is operating.

Juan PEÑALVER and Salvador SANCHEZ

Figure 2: a) (top) no mobile phone transmission, b) (middle) mobile phone transmission at 2 meters distance, c) (bottom) mobile phone transmission at 8 meters distance.
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next up previous
Next: VESPA is operational Up: IRAM Newsletter 54 (December 2002) Previous: New IRAM web site