they must be included in the dynamic range specification. The low end of the range is governed by the sensitivity of the set. Usually the minimum discernible signal (MDS) is used. This is the 178 Newnes Guide to Radio and Communications Technology weakest signal that the set can hear, and it is usually taken as a signal equal to the noise produced by the set. Often the signal may be around -135 - dBm for a 3 kHz bandwidth. At the other end of the range there are two main limiting factors. One is the onset of blocking, and this may be at the point where sensitivity is reduced by either 1 dB or 3 dB. The other is the generation of intermodulation products. Here the point that is often taken is the level of input signals which generate signals which could mask a signal equal to the minimum discernible signal, i.e. the noise floor. Typically sets have an intermodulation limited dynamic range of between 80 and 90 dB whereas the blocking limited dynamic range may be around 110 dB or more. The dynamic range is usually limited by the performance of the front end stages of the set. Not only is the noise performance of these stages critical, but SO too is the strong signal handling performance. Transmitters Today there is an enormous variety of different types of transmitter used to generate all the signals that can be found in the radio spectrum. Their purpose is to generate the basic signal or carrier, and then superimpose the modulation onto it in the correct format. Once this is done the signal is amplified to the correct level and filtered to remove any spurious products that are outside the required band. At this stage the output stages may also include matching circuitry to ensure that there is an accurate impedance match between the load and the transmitter. In this way the maximum power transfer takes place. Today transmitters take a wide variety of forms. Usually they are paired with a receiver SO that two-way communications can take place. Often units that contain a transmitter and receiver are called a transcei