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Capacitor Characteristics

The capacitor used to tune the Loop Antenna can be of various types. Depending on the type of capacitor you use you will see varying degrees of tuning sharpness. This is due to a parameter called the Q of the capacitor. The Q value refers the quality of the component as far as energy loss is concerned. Stated verbally, the Q of a component is the ratio of the energy stored to the energy lost.

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A Capacitor with a higher Q value is more efficient and therefore the circuit will tune more sharply and thus have a lower bandpass. This helps to tune in the desired VLF signal and reject unwanted noise and signals with a frequency close to that which you are monitoring.

Below is table of the Q value for different types of capacitors. The difference lies in the material used in the construction of each type.

 

  Q
(1 Khz)
Temperature
Coefficient (ppm)
Temperature Range (°C) Comments
Mica 600 0 to +70 -55 to +125  
Polystyrene 2000 -150 ±50 -55 to +85  
NPO Ceramic 1500 ±30 -55 to +125 Small Size
Polypropolene 3000 -115 -55 to +125  
Glass 1500 140 ±25 -55 to +125  
Polycarbonate 500 -50 -40 to +100  
Mylar 100 large -55 to +85  
Polyester 100 -160 -40 to +100  
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