THE FIRST GEODETIC VLBI EXPERIMENT AT 22GHZ BETWEEN JAPAN AND ITALY

Geodetic VLBI experiments are usually conducted at S and X bands. Sign ificant advantages could be gained making observations at a higher fre quency band like, for example, the 22 GHz (K band), where many radioas tronomical observatories have suitable receivers. In order to check th e feasibility and reliability of this new configuration, we organized a VLBI experiment, on February 1991, between the Kashima 34 m antenna in Japan and the Medicina 32 m radiotelescope in Italy. A new phase ca libration system, suitable for operation at K band and developed at CR L, was used at that time with both antennas. This phase calibrator uti lizes an ''up-conversion'' method which can be modified to operate at any other receiving frequency band. From this experiment we obtained c orrelated amplitudes, delays and delay rates for 152 observations of 3 1 radio sources. The rms residuals have been found to be 100ps for del ay, and 74 fs/s for delay rate. These values are comparable to present S/X solutions in spite of the fact that, for technical reasons, we ha ve not been able to implement all the possible improvements associated with the K band operation. To overcome the problem of a larger cohere nce loss due to higher atmospheric instabilities at K band, we have de vised a method to compute the correlated amplitudes which accounts for this effect.