Sub-carrier discriminators for telemetry

Frequency Division Multiplexing systems require some form of sub-carrier discriminators to recover the data from the individual frequency channels. A four-channel FM/AM telemetry system has been designed and developed for use in rocket-borne instrumentation and for data analysis four sub-carrier discriminators have been made. An unbalanced trigger circuit type ot discriminator is found to be preferable to the conventional Foster-Seely discriminator or the counting type discriminator. The channel selection is carried out by using passive filters which have been designed for the required characteristics. The output is amplified by a D.G. amplifier and feeds directly a pen-recorder. Overall performance is quite satisfactory, with a dynamic input range of 30 db., and an inter-channel rejection of 40 db. Linearify is better than 2% in the channel. The performance can be considerably improved by the use of better filters which is actually the limiting factor now.