Here are a few calculators for electronic/radio circuits. They are quite crude, but they work. Note that these formulas now accept "floating point" variables (an inductance value of 0.01 is a valid number).

## Resistors In Parallel (or Capacitors in Series)

Formula: Effective Resistance = (R1 x R2) / (R1 + R2)
(all units are the same, Ohms/Farads etc.)

 R1 R2 Effective Resistance

## Reactance of a Capacitor

Formula: Reactance = 1 / (2 * Pi * F * C)

 Freq (Hz) [F] Cap (pF) [C] Reactance (Ohms)

## Calculator Instructions

I have included a few calculators here. Each time you see the text [Enter] you are being asked to enter data in the field. If you have previously used another calculator then there will already be default start values entered for you. These are the results of your previous calculaton. You may of course enter new values.

## Capacitors (C1, C2 & C3)

C1, C2 and C3 are all in series and so form a single tuning capacitor of about 60pf. The ratios of C2:C3 determine the gain and their values may vary quite a lot. In general, C2 = 3x wavelength, C3 = 9x wavelength. C1 can be any value from 1x wavelength to 10x wavelength and is normally chosen to fine-set the frequency of the oscillator. Make C1 start value about the same as C2. The actual values can vary over quite a wide range. This calculator will calculate the total tuning capacitance for your own selected values.

 [Enter] Frequency (MHz) Enter a frequencythen click the button [Enter] C1 (pf) [Enter] C2 (pf) [Enter] C3 (pf) You may enter newC1/C2/C3 cap values Tuning Capacitance (pf)

In the above calculator, enter a frequency and click the "SHOW C1, C2 & C3" button and the values of C1, C2 & C3 will be displayed. If you then click the "SHOW CAPACITANCE" button, you will see the value of the effective tuning capacitor that will be resonated with L1. You may also enter your own C1, C2 and C3 values to find the effective tuning capacitor that will be resonated with L1.

## Inductor (L1)

The inductor L1 resonates with the total capacitance above to determine the operating frequency. If you know the capacitance, having just read the the previous chapter, then use your basic frequency (transposed) to give inductance, or plonk your values in this little calculator:

 [Enter] Capacitance (pF) [Enter] Frequency (MHz) Inductance (uH)

## Coil Winding

Now you know the inductance and the capacitance, it is just to buy and insert those values into the circuit. But if you really want to wind the coils yourself, then you will probably use either air-cored 6mm Dia. formers, or use formers with a ferrite core. There are precise formulas to use but I like this method. Insert the required inductance and click the button.

 Turns (Ferrite core) Turns (6mm Dia. Air) [Enter] Inductance (uH)

Please remember that this last "calculation" is very approximate since a lot depends upon the individual former. The "Ferrite core" is assumed to be a re-wound IF can.

## Reactance of an Inductor

Formula: Reactance = 2 * Pi * F * L

 Freq (Hz) [F] Induct (uH) [L] Reactance (Ohms)

## Basic frequency

Formula: Frequency (F) = 1 / (2 * Pi * Sqrt(LC))

 Capacitance (pF) [C] Inductance (uH) [L] Frequency (F)(Hz)

## Single Layer Coil

 Formula:

 Inductance (uH) [L] Length of Winding [l] Coil Outside Radius [r] All sizes in millimeters Turns required [N]

## Multi-Layer Coil

 Formula:

 Inductance (uH) [L] Winding depth+Form Dia [a] Winding Length [b] Winding Depth [c] Turns required (All sizes in millimeters)

## Heatsink Evaluation

Calculates the effective temperature rise coefficient of a measured heatsink. Area is EXPOSED surface area of heatsink in square centimeters.

 Formula: Degrees Centigrade per Watt = 50 / Sqrt(Area sq-cm )

 Area (sq-cm) [A] Exposed areas only. Degrees C / Watt

## Heatsink Calculation

Calculates heatsink surface area needed for a given heatsink temperature coefficient.

 Formula: Area Required (sq-cm) = Sq (50/C-watt)

 Degrees C / Watt Exposed areas only Area Required (sq-cm)

## Attenuators - "T" and "H" Type

 Formulas:

The Input/Output powers may be in any electrical unit you prefer, eg: Meggawatts, Picowatts, Joules, Hamster-treadmill revolutions per hour etc.

 Enter Input Power Enter Output Power Enter Input Impedance Enter Output Impedance R1 value (for unbalanced) R2 value (for unbalanced) R1/2 value (for balanced) R2/2 value (for balanced) R3 value

Negative values of resistance occur when impossible values of input and output impedance and attenuation are entered. For example, it is not possible to drive a 50-ohm line from a 600-ohm line and have a voltage attenuation factor of less than 6.78

## Attenuators - Square (or Box) Type

 Formulas:

The Input/Output powers may be in any electrical unit you prefer, eg: Meggawatts, Picowatts, Joules, Hamster-treadmill revolutions per hour, etc.

 Enter Input Power Enter Output Power Enter Input Impedance Enter Output Impedance R1 value R2 value R3 value (for unbalanced) R3/2 value (for balanced) SM0VPO

Again, negative values indicate an impossible attenuation situation.