A system to reduce noise includes a noise measurement device that provides a measure of noise associated with a digital input video signal. In other embodiments, a single diffraction grating is used to combine a plurality of different wavelengths, wherein the input laser beams are obtained from very narrow linewidth sources to reduce chromatic dispersion. Corresponding apparatus are also provided. The amount of immunogen that is released from the implant into the bird is preferably sufficient to effectively stimulate a primary immune response to the immunogen. The vacuum envelope within which the electron gun is contained includes the Kovar support and a flexible member with which it makes a vacuum seal, this member being of copper.