How does a frequency extender work?

In the Test & Measurement field, a frequency extender is an electronic device that extends the frequency range of the equipment that it is used with. It is designed to use and convert the excitation signals provided by the test equipment, and seamlessly extend its standard frequency range to the required band. Conversion of the frequencies supplied by the T&M equipment can be achieved by means of frequency multiplying, mixing or combination of both, which is the case in more complex frequency extension systems. To learn more about the various types of frequency extenders please refer to ‘What are the different of frequency extenders?’

A harmonic mixer is an example of a frequency extender, that can effectively extend the coverage of a spectrum or a signal analyzer by means of using a low frequency LO signal supplied by the analyzer and performing down-conversion at a harmonic of this frequency. In this case, the mixing occurs in accordance with a formula IF = RF ± Nx LO, where N is a harmonic number. The IF signal is supplied back into the analyzer for analysis. This way a high frequency RF signal that lies far beyond the standard frequency range of the analyzer can be detected and down-converted by a frequency extender to an intermediate frequency that the analyzer can work at. 

A frequency extender can also be used to help generate high frequency signals and in such applications, it can be interfaced with a signal source or a signal generator. In this case, the extender multiplies the input signal supplied by the generator to a frequency that the extender is intended to work at, which happens in accordance to the formula FOUT = N x FIN, where N is multiplier factor. Typically, that means that the output frequency is a fixed multiple (i.e. 2, 3, 6, 12, 18 etc.) of the input frequency. 

For more complex Test & Measurement systems where there is a need for signal generation as well as analysis, more sophisticated extension systems are required that use a combination of both mixers and multipliers to provide the required functionality.  

Regardless of the type of frequency conversion and the level of complexity, frequency extenders are intended to interface seamlessly with the dedicated T&M equipment by being compliant with the frequencies and signal levels that such equipment supplies. In many instances, the equipment itself is intended to work in a frequency extension mode and is fitted with the required hardware and software options, and can be easily configured via the user interface.