Noise cancellation bridges

This chapter deals with the explanation of noise cancellation bridges. Getting rid of noise battering a signal is a major chore. There are a number of different techniques for overcoming noise, the method described herein can be called the “invert and obliterate” approach. The signal from the main antenna is a mixture of the desired signal and a locally generated noise signal. This noise signal is usually generated by the 60 Hz alternating current (AC) power lines, or machinery and appliances operating from the 60 Hz AC lines. The noise signal is not confined to 60 Hz, but will extend into the VHF region because of harmonic content. The noise spikes appear every 60 Hz from the fundamental frequency up to about 200 MHz or so, although the harmonics become weaker and weaker at progressively higher frequencies. But in the VLF bands, AM broadcast band (AM BCB), and shortwave bands, the noise signal can be tremendous. Therefore, it causes a huge amount of interference. The solution is to invert the noise signal, and combine it with the signal from the main antenna. When the phase inverted noise signal combines with the noise signal riding on the main signal, the result is cancellation of the noise signal, leaving the resultant main signal.