ply adding a CR network to the modulating signal that integrates the modulating signal. Phase shift keying Phase modulation may be used for the transmission of data. Frequency shift keying is robust and has no ambiguities because one tone is higher than the other. However, phase shift keying (PSK) has many advantages in terms of efficient use of bandwidth. The problem with phase shift keying is that the receiver cannot know the exact phase of the transmitted signal to determine whether it is in a mark or space condition. This would not be possible even if the transmitter and receiver clocks were accurately linked because the path length would determine the exact phase of the received signal. To overcome this problem PSK systems use a differential method for encoding the data onto the carrier. This is accomplished, for example, by making a change in phase equal to a one, and no phase change equal to a zero. Further improvements can be made upon this basic system and a number of other types of phase shift keying have been developed. One simple improvement can be made by making a change in phase by 90 degrees in one direction for a one, and 90 degrees the other way for a zero. This retains the 180 degree phase reversal between one and zero states, but gives a distinct change for a zero. In a basic system not using this process it may be possible to lose synchronization if a long series of zeros are sent. This is because the phase will not change state for this occurrence. There are many variations on the basic idea of phase shift keying. Each one has its own advantages and disadvantages enabling system designers to choose the one most applicable for any given circumstances. Minimum shift keying It is found that binary data consisting of sharp transitions between 'one' and 'zero' states and vice versa potentially creates signals that have Modulation 65 sidebands extending out a long way from the carrier, and this is not ideal from many aspects. This can be overcome in part by filtering the signal, but is found that t