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.
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 |