The Effelsberg 100m radio telescope takes part in observations scheduled as part of the VLBI "High Sensitivity Array" (HSA). These are observations together with the NRAO VLBA and at least 2 of the following additional telescope: Effelsberg 100m, VLA (phased array), GBT, ARECIBO.
Effelsberg can be used at the HSA observing frequencies of 1.4/1.6, 5, 8.4, 15, 22 and 43 GHz. All these receivers have dual circular polarization.