DESIGN AND TESTING OF A PHASELOCK RECEIVER FOR A V.H.F. - F.M. IONOSPHERIC FORWARD SCATTER COMUNICATION SYSTEM

Abstract

In this thesis, a start has been made on the design of a low power frequency modulated VHF ionospheric forward scatter communication system, to provide reliable radio transmission between points located in the auroral zone. Previous work suggested the feasibility of a system using a 50 watt transmitter and a phaselock receiver with a lock range of 300 cps and signal bandwidths between 5 and 100 cps. To substantiate former work in which recommendations were based on test results using an unmodulated carrier, a similar system was designed with provisions for frequency modulation. Dictated by the frequency stability of the entire system, the lock range was increased to 775 cps. Much of this thesis is devoted to the design and analysis of the phaselock detector and to the testing of the receiving system. Some pertinent properties of the receiver have been theoretically predicted and tested under simulated field operating conditions. In order to test the system under actual field conditions the 50 watt transmitter and the phaselock receiver were placed at Uranium City and Saskatoon, Saskatchewan, respectively. It was observed that sufficient signal to lock the system could e received for only a small portion of the total propagation time. This fact tentatively has been attributed to the effect which Doppler frequency shifts may have on a phaselock system with a relatively large lock range. The geometry of propagation and atmospheric conditions were not as favourable as during previous experiments. Recommendation have been made regarding improvements of the present receiver design and regarding the analysis of other, possibly superior, receiving systems.