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ExtraClassSylalbus2009jan-AD7FO

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Rev 2.02<br />

Capacitors in series<br />

C= ___________________1__________<br />

1 1 1 ….._1__<br />

C1 + C2 + C3 + Cx<br />

Reactance<br />

Reactance is the equivalent AC resistance of a capacitor or inductor at a given frequency<br />

For an inductor, XL =2πFL<br />

XL =2πFL frequency is in Hertz and Inductance is in Henries. or Mili-Henries and Kilo-<br />

Hertz or Micro-Henries and Megahertz<br />

Example 20 mH inductor at 3.5 KHz<br />

XL =2πFL = 6.28 x .02 x 3,500 = 6.28x 70 = 439.8 Ω<br />

OR<br />

XL =2πFL = 6.28 x 20 x 3.5 = 6.28x 70 = 439.8 Ω<br />

OR<br />

XL =2πFL = 6.28 x 20,000 x .0035 = 6.28x 70 = 439.8 Ω<br />

For a capacitor<br />

Reactance (Xc) is equal to 1/ (2π FC) frequency is in Hertz and Capacitance is in Farads. or Microfarads<br />

and Megahertz<br />

Example 20 µF Capacitor at 3.5 KHz<br />

Xc =1/(2πFC) = 1/(6.28 x .000,020 x 3,500) = 1/(6.28x .07) = 2.27 Ω<br />

OR<br />

Xc =1/(2πFC) = 1/(6.28 x 20 x .0035) = 1/(6.28 x .7) = 1/.44 = 2.27 Ω<br />

RC Time Constant<br />

TC = C * R farads - ohms or microfarads – megohms<br />

Charge vs number of time constants<br />

Time Constant % Charge /<br />

Discharge<br />

1 63.2<br />

2 86.5<br />

3 95<br />

4 98.2<br />

5 99.3<br />

dB Calculations<br />

Power dB = 10 * LOG (P1/P2) P1 andP2 must be the same i.e.: µWatts. Miliwatts or Watts<br />

Voltage - dB = 20 * LOG (V1/V2) V1 and V2 must be the same i.e.: µvolts. Milivolts or Volts<br />

The following table will allow you to quickly estimate dB gain or loss. The one and two dB values are close enough to get you<br />

to the correct answer in the test.<br />

Gain<br />

(+)<br />

dB Loss (-)<br />

x 1.2 1 80%<br />

x 1.6 2 63%<br />

x 2 3 50%<br />

x 4 6 25%<br />

x 10 10 10%<br />

Jack Tiley <strong>AD7FO</strong> Page 105 3/15/2009

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