In this proceedings, preliminary results of the KVN Source-Frequency Phase-Referencing (SFPR) observation of 3C 66A and 3C 66B are presented. The motivation of this work is to measure the core-shift of these 2 sources and study the temporal evolution of the jet opacity. Two more sources were observed as secondary reference calibrators and each source was observed at 22, 43, and 86 GHz simultaneously. Our preliminary results show that after using the observations at the lower frequency to calibrate those at the higher frequency of the same source, the residual visibility phases for each source at the higher frequencies became more aligned, and the coherence time became much longer; also, the residual phases for different sources, within 10 degrees angular separations, follow similar trends. After reference to the nearby calibrator, the SFPRed maps were obtained as well as the astrometric measurements, i.e. the combined coreshift. The measurements were found to be affected by structural blending effects because of the large beamsize of KVN, but this can be corrected with higher resolution maps (e.g. KAVA maps).

ABSTRACT
1. MOTIVATION
2. METHOD AND OBSERVATIONS
3. PRELIMINARY RESULTS OF THE FIRST EPOCH
    3.1. Frequency Phase Transfer
    3.2. Maps and Astrometric Mesurements
4. DISCUSSION AND SUMMARY
REFERENCES

• Guang-Yao Zhao(Korea Astronomy and Space Science Institute)
• Taehyun Jung(Korea Astronomy and Space Science Institute)
• Richard Dodson(Korea Astronomy and Space Science Institute/International Centre for Radio Astronomy Research)
• Maria Rioja(Korea Astronomy and Space Science Institute/International Centre for Radio Astronomy Research)
• Bong Won Sohn(Korea Astronomy and Space Science Institute)