The First Absolute Delay Determination of GLONASS Time Receiver for TAI Time Transfer Link Calibration

According to GLONASS ICD [1] UTC(SU) is a reference time scale for GLONASS System Time (GLO ST). That’s why one of continuous tasks of VNIIFTRI is to monitor actual time difference between UTC(SU) and GLO ST and conformity to this value of the ?c = UTC(SU) + 03h00m + GLO ST, broadcasted in GLONASS navigation message. VNIIFTRI started such monitoring since end of 80th [2, 3]. Ever since that time, have been used many receiver’s type in VNIIFTRI for monitoring. Each step of receiver change included relative calibration procedure to maintain UTC(SU) – GLO ST continuous. Now we use TTS3, TTS4 receivers for this purpose. Peter Daly from Leeds University has developed the beginner of GLONASS receivers in western countries. Since that time, have been changed a few generations of the receiver and every new model has been calibrated against previous one to ensure measurement continuity [2, 3]. From very beginning, there was about 200 ns difference in UTC-GLO ST monitoring data originated from VNIIFTRI [4] and the BIPM publications [5] based on western laboratories measurements data. Moreover, even GLONASS control segment itself was not sure which data is more accurate VNIIFTRI or BIPM. VNIIFTRI has arranged current work on measurements and calibration in three steps. At the first one, we produced differential comparisons between delivered from the BIPM receiver (TTS4 #136) and VNIIFTRI receivers type TTS3 #026 (master) and type TTS4 #119. The receiver TTS #026 have been 7 years before differentially calibrated against portable one delivered from BIPM. The next step was TTS4 #136 absolute delay determinations consisted of receiver itself, antenna and antenna cable, so called end-to-end delay of the whole complex for L1C, L2C, L1P, and L2P for GLONASS and GPS. At during the last step we introduced delays obtained during previous step into TTS4 #136 and produced once more differential comparisons relative to VNIIFTRI receivers type TTS3 #026 (master) and type TTS4 #119.