Postila, M.1, Wannberg, G.2, Rietveld, M.3, Iinatti, T.1 and Westman, A.4
1 EISCAT Scientific Association, Sodankylä, Finland
2 EISCAT Scientific Association, Kiruna, Sweden
3 EISCAT Scientific Association, Tromsų, Norway
4 EISCAT Scientific Association, Longyearbyen, Norway
A major upgrade of the EISCAT Heating facility is currently underway. The thirteen HP analogue synthesizers that are the key part of the Heating modulator are getting quite old, are slow and have a major drawback of starting with a random phase, which makes setting them up a tedious manual procedure. In addition of replacing them by direct digital synthesizers (DDS), another aim in the Heating upgrade is to add proper receiving capability to the system, by converting one of the transmission antenna fields for reception and building a complete receiver unit for it. A key requirement has been to keep the upgrade costs to a minimum, by using as much as possible existing leftover and spare parts from all over the EISCAT system.
Planning for the upgrade started in the spring 2004; in January 2006, first proof-of-concept tests of the new DDS-based modulation unit were performed at the Heating facility. Apart from revealing some lack of driving power in the prototype synthesizer, the initial test was successful and showed that the prototype synthesizer was working well in the noisy environment. In 2006, a dedicated VME-crate was constructed to house the synthesizer board and other equipment needed for the transmission control, such as a radar controller. In 2006, also the UNIX software needed to create and download the amplitude-modulation waveform to the synthesizer was much improved.
In January 2007, a second test period at the Heating site confirmed that the integrated prototype system was now capable of driving the Heating power amplifiers without problems, with freely selectable amplitude modulation. At the time of writing (April 2007), the DDS design is being finalized so that it can be sent out to a vendor for replication. A major job that is still in an early phase is to arrange UNIX control for all the 100+ analog signals needed to handle the various parts of the Heating transmitter. Nevertheless, it is hoped that the upgrade can be taken into operational use before the end of 2007.