  For the sake of high-sensitivity 6.7 GHz methanol maser observations, we
developed a new technology for coherently combining the two signals from the
Hitachi 32 m radio telescope and the Takahagi 32 m radio telescope of the
Japanese Very long baseline interferometer Network (JVN), where the two
telescopes were separated by about 260 m. After the two telescopes were phased
as a twofold larger single telescope, the mean signal-to-noise ratio (SNR) of
the 6.7 GHz methanol masers observed by the phased telescopes was improved to
1.254-fold higher than that of the single dish, through a Very Long Baseline
Interferometry (VLBI) experiment on the 50 km baseline of the Kashima 34 m
telescope and the 1000 km baseline of the Yamaguchi 32 m telescope.
Furthermore, we compared the SNRs of the 6.7 GHz maser spectra for two methods.
One is a VLBI method and the other is the newly developed digital position
switching, which is a similar technology to that used in noise-cancelling
headphones. Finally, we confirmed that the mean SNR of method of the digital
position switching (ON-OFF) was 1.597-fold higher than that of the VLBI method.
