Imortance of Power
The output power level of a system or component is frequently the critical factor in the design, and ultimately the purchase and performance of almost all radio frequency and microwave equipment. The first key factor is the concept of equity in trade. When a customer purchases a product with specified power performance for a negotiated price, the final production-line test results need to agree with the customerˇŻs incoming inspection data. These shipping, receiving, installation or commissioning phases often occur at different locations, and sometimes across national borders. The various measurements must be consistent within acceptable uncertainties.
Secondly, measurement uncertainties cause ambiguities in the realizable performance of a transmitter. For example, a 10-W transmitter costs more than a 5-W transmitter. Twice the power output means twice the geographical area is covered or 40% more radial range for a communication system. Yet, if the overall measurement uncertainty of the final product test is on the order of ˇŔ0.5 dB, the unit actually shipped could have output power as much as 10% lower than the customer expects, with resulting lower operating margins.
Because signal power level is so important to the overall system performance, it is also critical when specifying the components that build up the system. Each component of a signal chain must receive the proper signal level from the previous component and pass the proper level to the succeeding component. Power is so important that it is frequently measured twice at each level, once by the vendor and again at the incoming inspection stations before beginning the next assembly level. It is at the higher operating power levels where each decibel increase in power level becomes more costly in terms of complexity of design, expense of active devices, skill in manufacture, difficulty of testing, and degree of reliability.