Friday, 17 August 2012

EISCAT UHF conversion to VHF

The EISCAT Council, on recommendation from the EISCAT Science Oversight Committee (SOC), decided that the remote UHF receivers located at Kiruna, Sweden, and Sodankylä, Finland, should be converted to the current VHF frequency of 224 MHz. The background to this is that the UHF frequency of 930 MHz lies within the radio band, which is nowadays used for GSM mobile communication, and the frequency protection, which was in place at the remote sites, has ended a while ago. In Sodankylä, e.g., we have noticed in autumn 2011, that new transmitters had come on-line, which makes incoherent scatter observations impossible due to interference. Thus the EISCAT Scientific Association has lost its unique capability of tristatic ISR measurements.

In order to preserve this ability, a plan has been made to convert the UHF 32-m parabolic dishes to 224 MHz in order to receive echoes of the Tromsø VHF radar signal when the radar points to zenith. Unfortunately, the VHF is not allowed to point further south than zenith, but it is estimated, that even at zenith, the remote sites will see the VHF signal. Astonishingly, even though the remote antennae are designed for the higher frequency, when considering all advantages and disadvantages of the conversion, they should perform at the VHF frequency just as well as at the UHF frequency.

The conversion is taking place during the present summer and is expected to be completed before the winter sets in again. Here are some photos sent to us by Director Esa Turunen.

Lars-Göran Vanhainen of EISCAT Kiruna explains the changes to Jorge Chau, Director of the Jicamarca Radio Observatory.

The dipole ring feed, which is going to replace the secondary reflector in the 32-m dish antennae, i.e. the small mirror suspended by the tripod.

Lars-Göran Vanhainen explaining the front-end to Jorge Chau.

A close-up of the front-end.

Aluminium frame, onto which the base plate of the ring feed will be mounted.
With these photos and news of the latest development at EISCAT, we wish all of you a very happy weekend!

Photos: Esa Turunen.

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