All communications signals experience noise when transmitting from one point to another. This noise is additive meaning it will mix itself with the transmitted signal changing its waveform. This changing of the waveform is called distortion. Distortion can change the information transmitted thus causing misinformation or unreliability in signal transmission. This type of error is detrimental to a submarine, where receiving information is vital to the very survival of the submarine. For example, if a submarine were receiving informatin as to the bearing and speed of any enemy submarine. Let's say the bearing number was changed in error from 30 degrees, which is 11110 in binary, to 10110, which is 22 degrees. We see the submarine has the wrong information and now its survivability is jeopardized because of misinformation.

In communications, there are many types of noise present which can cause a signal to be misrepresented. White noise is a type of noise characterized by a constant power spectral density across the frequency spectrum. Thermal noise is produced by the random motion of electrons in a medium. The intensity of this motion increases with increasing temperature and is zero only at a temperature of absolute zero. Most noise is characterized as Guassian meaning that its density function is specified by the mean or average. What need to be done is to have a system which will ensure security of information and eliminate any noise present in the transmitted signal.


The solution to this problem is to design a digital bandpass filter which will filter out any noise and pass only the signals which contain the pertinant information. The passband of the filter will be between 15 and 16 kHz. The attenuation is going to be greater than 50 dB with a passband attenuation of less than .5 dB. The transition width of the filter should be around 1 kHz. Digital filters have an advantage over their analog counterparts. They are compact, meaning that many filters can be made on a single integrated circuit saving space and weight. Digital filters are temperature independent, meaning that the function of the filter will remain the same despite the variation of temperature. Temperature can have an adverse effect on analog filter operation. Digital filters have a sgarp cutoff as to analog filters which have a slow sloping like transition curve. This makes the digital filter have an operation which is almost digital like. The digital filter will be employed on the Motorola 56002 Digital Signal Processor.