Hi Sergey,
looking at your screenshots, you seem to be struggling with a lot of local interference. I have wondered about the absence of 6.25 Hz Chayka lines, specifically 137775.0 Hz and 137781.25 Hz. Your closest station (Petrozavodsk) is only 270 km from Petersburg and ~ 240 km from Gruzino, so the lines should be visible strongly during day and night. Perhaps the noise blanker is over-active and cutting out the Loran pulses? You could also try to tune to 100 kHz and listen to the 1 kHz "dit dit dit" with AM demodulation.
73, Markus