1. The rate of transfer or absorption of energy per unit time in a system . ( 188 ) 2. Whenever the power of a radio transmitter etc. is referred to, it shall be expressed in one of the following forms, according to the class of emission , using the arbitrary symbols indicated:
peak envelope power (PX or pX);
mean power (PY or pY);
carrier power (PZ or pZ).
For different classes of emission , the relationships between peak envelope power , mean power and carrier power , under the conditions of normal operation and of no modulation , are contained in CCIR Recommendations which may be used as a guide. For use in formulae, the symbol p denotes power expressed in watts and the symbol P denotes power expressed in decibels relative to a reference level. [ NTIA ] [ RR ]