is resistive then they will be in phase. Very high power amplifiers like those used as the final stage for a broadcast transmitter may be capable of delivering 100 kilowatts or more to the antenna, whereas those used for local broadcast stations may only deliver 100 watts or SO. Other types of transmitter can deliver a variety of power levels dependent upon their use. Cellular phones can typically deliver around a watt, but this will vary according to their application and the type of system in use. Power levels are often measured directly in watts. However, they are often specified in decibels relative to a watt or a milliwatt. Given the units dBm (decibels relative to a milliwatt) and dBW (decibels relative to a watt), they are being used increasingly. Using this system it is very easy to incorporate any changes in level brought about by the use of amplifiers, attenuators, losses in feeders, etc. All of these are generally expressed in decibels SO it is simply a matter of adding or subtracting the relevant figure from the power level, e.g. a power of 10 dBW becomes only 6 dBW at the end of a feeder with a 4 dB loss. For transmitters, the Transmitters Table 6.1 dBm-dBW-watts conversion Watts Terminology 10 000 000 10 megawatts 1 000 000 1 megawatt 100 000 100 kilowatts 10 000 10 kilowatts 1 000 1 kilowatt 100 watts 10 watts 1 watt 100 milliwatts 10 milliwatts 0.001 1 milliwatt 0.0001 100 microwatts 0.00001 10 microwatts 0.000001 1 microwatt 0.0000001 100 nanowatts 0.00000001 10 nanowatts 0.000000001 1 nanowatt power levels are generally expressed in dBW, whereas levels in dBm are generally used for low power circuits. For example, a diode ring mixer may require a local oscillator input of 7 dBm. It is important to ensure that an amplifier operates under the correct conditions. When there is a poor impedance match between the amplifier and its load it will operate under conditions that are not ideal. Amplifiers are designed to operate into a given load. This is normally 50 ohms for which suitable feeders are avai