ABSTRACT
A more ‘purist’ solution is offered by the up-conversion or heterodyne philosophy. Here a separate video modulator, usually running at 70MHz, is mixed with a suitable SHF pump frequency so that one sideband provides the required SHF channel frequency. FM deviation present at the modulator will be directly translated to the output frequency. FM noise is inherently easier to control with this system
concept as the pump generator largely responsible for generation of the microwave frequency is unmodulated and can have a narrow loop bandwidth. In addition, deviation is unaffected by the mixing process, and modulator noise contribution is hence not magnified (as with subsequent multiplication in the direct modulation system).
