Yu.E. Kalinin - Dr.Sci. (Phys.-Math.), professor, head of the department of physics of solid state, Voronezh state technical university, department of radio engineering
V.A. Kozmin - Ph.D. (Eng.), associate professor, Director of research JSC «IRKOS» (Moscow). E-mail: kv@ircoc.vrn.ru
I.B. Kryzhko - Ph.D. (Eng.), senior research scientist, JSC «IRKOS» (Moscow). E-mail: kryzhkoib@ircoc.vrn.ru
A.V. Polyakov - Head of DSP sector, JSC «IRKOS» (Moscow). E-mail: polyakovav@ircoc.vrn.ru
A.A. Salikov - Post-graduate student of Voronezh State Technical University. E-mail: salikovaa@ircoc.vrn.ru
A.B. Tokarev - Ph.D. (Eng.), associate professor of Voronezh State Technical University; head of research sector, JSC «IRKOS». E-mail: TokarevAB@ircoc.vrn.ru

This paper is dedicated to the TDOA-system radio receivers synchroni¬zation problem. PPS pulses of timing GPS-receivers can be used as basis for local time scales (LTS) synchronization for spatially separated radio receivers. The PPS pulses are unacceptable as finish LTS, because their actual placement on the time axis demonstrates significant fluctuations. Also, there are some situations, when it is impossible for GPS-receivers to form PPS-pulses. Therefore, LTS may be constructed on the basis of high-stability reference generators (RG) synchronized with each other by long PPS-pulse sequences. The existence of internal RG-frequency micro corrections, carried out at random moments of time, must be taken into account while developing the synchronization subsystem. These micro corrections complicate the tuning of LTS and do not allow to ensure the required accuracy of synchronization using the RG-frequency direct tuning only. To minimize LTS and UTC jitter it is recommended to use soft compensation of random deviations based on digital filtering. To ensure rapid start of synchronization subsystem the LTS synchronization algorithm must be multistage. At the initial stage the primary evaluation of the LTS parameters are carried out on the basis of least-squares method. The purpose of subsequent stages is LTS tuning by using the Kalman filter or similar filters with constant coefficients. Developed and implemented in radio monitoring equipment, manufactured by JSC «IRKOS» (Moscow), the synchronization algorithm demonstrates drift not exceeding ±30 ns, of mutual signals delays on long time intervals.