Passive TV technique for time transfer via Indian Satellite INSAT-1B

The use of TV signals for time comparison is a very well-known technique. The TV signal can be utilized both passively and actively for the same purpose. Recently, this technique has become popular with the use of geosynchronous satellites for TV transmission. Indian Satellite INSAT-1B transmits TV signals to have a full coverage over the Indian subcontinent. So, attempts are being made to utilize these TV signals for time transfer from the National Physical Laboratory (NPL), New Delhi, to other users in India. In the terrestrial TV network, differential propagation delay remains to be a constant factor unless there is a change in the network configuration. But in the satellite TV network, differential propagation delay does not remain constant because the satellite position with respect to the earth does change around its mean value due to the non-circular satellite orbit and nonzero inclination of the plane of the satellite orbit with respect to equatorial plane. So the maximum variations of differential propagation delay about its mean value have been worked out for different locations in India based on some theoretical calculations coupled with findings of some general behavior of INSAT-1B. These observations predict that the variation of differential propagation delay from its mean value will be within 10 μs for most parts of India and half of India will remain even within the range of 5 μs. These observations tally well with those obtained with the help of the actual predictions of satellite positions. Experimental data also corroborate these findings.