What Are Frequency Changers or Frequency Converters and What are Their Applications?

 In the simplest sense, frequency changer or frequency converter is a device which can change the frequency of an alternating current. It could be changing the frequency of the mains supply to match another grid like changing from a 50 Hz to 60 Hz which is used in another region. Another application is changing the frequency for use in aircraft electrical system for which the standard frequency is 400 Hz. So airports, aircraft hangars and ships need 400 Hz frequency converters. Higher frequency would mean lighter cables and transformers in the aircrafts, compared to standard 50 Hz power supply. Reducing weight of components is an important consideration in the design of aircrafts, as expected. 

In radio communications, frequency conversion is an important part of superheterodyne receivers. This is done using a frequency mixer where the received radio signals are mixed with a local oscillator signal to generate two frequencies. Mixing of two radio frequency signals produces one which is the sum of the two frequencies and another which is the difference of the two frequencies. In the superheterodyne receiver, the frequency sum is filtered out and the difference used as the intermediate frequency. Intermediate frequency signal is further amplified and used for detection, the process of separating the modulating signal which is the audio frequency. Thus all received frequencies are converted to a fixed intermediate frequency, often known as IF in short. This allows further processing at a fixed frequency rather than the widely varying frequency of radio signals from multiple bands.

Another situation in which frequency conversion is used is in satellite communications. Satellites typically receive signals in the uplink frequency band and convert them to signals in another band and transmit them down to Earth stations in the downlink frequency band. Amateur radio operators on Earth transmit signals on the uplink frequency band and receive them on the downlink frequency band. For example, the uplink of the Geostationary Amateur Radio Satellite Qatar Oscar 100 (QO 100) is in the 2.4 GHz band, while the downlink is in the 10 GHz band.

Still another important application is in the variable frequency drive used for controlling speed of alternating current motors and compressors of devices like air conditioner and refrigerators. They are usually called inverter air conditioners and refrigerators. The smooth modulation of compressor speed results in reduced wear and tear, better energy efficiency and more consistent temperature control. Another advantage is that the large surge current during each switch on of the conventional air conditioner is not there for the inverter compressor. The alternating current supply is first rectified into direct current, which runs an inverter, converting it back to alternating current of variable frequency and voltage. That is how the name 'inverter' came for the compressors of modern air conditioners and refrigerators, in contrast to conventional compressors which intermittently switch on and off.

Similar frequency conversion is also occurring in the commonly used switch mode power supplies as well. In them, usual 50 or 60 Hz alternating current mains supply is rectified into direct current and then run oscillators or switching circuits which generate high frequency alternating current. Transformers for higher frequencies are lighter and less expensive. The high frequency high voltage current is then stepped down to lower voltages, rectified, regulated and stable direct current output obtained. Only disadvantage for radio amateurs is that unless good radio frequency interference suppression filters are in place, switch mode power supply  known in short as SMPS, is an important source of radio frequency interference in radio receivers.