Radio Frequency Transformer

 

Introduction

• The range of radio frequency is from 30 kHz to 300 GHz . 
• The radio frequency transformer is classified on the basis of operating frequency.

      ( 1 ) Radio frequency transformer

      ( 2 ) VHF transformer

      ( 3 ) UHF transformer

Radio Frequency Transformer

• The range of radio frequency is from 30 kHz to 30 MHz  
• Figure shows simple radio frequency transformer, sometimes it tuned at particular frequency by connecting fixed capacitor to one winding.  
• The forms parallel LC resonant circuit with primary winding and therefore it has produces high frequency at particular parallel resonance frequency. 
• The inductance of such transformer is adjustable.

VHF Transformer ( Very High Frequency Transformer )

• The range of VHF transformer is from 30 MHz to 300 MHz 
• The inductance of the transformer winding is very kept very small and can be achieved by few turns of wire.

UHF Transformer 

• When conventional core is used for transformer at ultra high frequency ranges from 300 MHz to 300 GHz, the losses in the iron or ferrite cores are much higher. 
• In order to reduce losses, inductance needed can be provided by just few turns of thin wire or even small coils printed on the circuit board. 
• The inductance is plated with low resistivity material like silver due to flow of surface conductor at UHF. 
• The printed circuit board should be designed such that no components on it moves from its original position during serving otherwise change in inductance and capacitance greatly affected to nearby components.

 

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Electromagnetic Screening

• As the signal frequencies increases, electromagnetic interference increases, which is reduced by effective magnetic screening. 
• The electrostatic interference can be problem due to capacitance between transformer coils and nearby components of wiring. 
• A screening shied is connected to earth is used to prevent electrostatic effects. 
• The screening shield is made from low resistivity and low reluctance material such as permalloy or Mu – metal.