I made the experience that with the occurrence of the first mathematical equation many radio amateurs give up. But that does not have to be. On this webpage I offer the calculation of simple circuits and other things from the range of the amateur radio as forms. Their use is easy, so each one can use it.
If you want to know, how looks the equations used into the scripts, then see the mathematical background at the end of each webpage.
 
Resistors
 

 
Capacitors
 

 
Resonant circuits and LC networks
 

Parallel connections of resistors
 
In the meantime are resistors avaiable of the series E24 and E96 with tolerance of 1 % relativ inexpensive. So the usuable 24 or 96 values in each decade, which have at one's disposal, shold be sufficient for homebrewer. But if one need resistors with higher power dissipation, one can fall back only on resistors of the serie E12. You can use the calculation to determine the nonexistent values, parallel connections of up to 5 resistors are possible.

Attenuators
 
If the output level of a stage is too high, in order to be led directly to the input of another, one scolded attenuators between them. You can use the calculation of attenuators for it.
But only rarely resistances are available in the computed values. Change on the specified page the calculated resistances against from you used and see, which deviations with it to arise.
If larger power must be processed, you can use the calculation of power attenuators to determine additionally the necessary power dissipations for individual resistors.
At the attenuators were used so far, the input and output impedances are equal. However if different impedances must be adapted somehow, it can be also used resistors for it. The calculation of the loss arising inevitably with it determine the calculation of attenuators with minimum loss.
Since no coils or capacitors are used in the 3 circuit above, the matching takes place frequency-independently. Attenuators are suitable therby for the wide-band matching.

Signal splitters with resistors
 
Sometimes it is necessary to divide an output signal on several building groups. Also this is realizable with resistors. The calculation of the loss arising inevitably with it determine the calculation of signal splitters. Since no coils or capacitors are used, the matching takes place frequency-independently. Attenuators are suitable therby for the wide-band matching.

Band spreads with variable capacitors
 
A variable capacitor is rather rarely directly applicable in a circuit. If the tuning range is too largely and/or the initial capacity is too small, the desired values can be reached nevertheless by two additional capacitors. Frequently this is used as so called band spread in a VFO. You can use the calculation of the band spread for it.
But only rarely capacitors are available in the calculated values. Change on the specified page the calculated capacitors against from you used and see, which deviations with it to arise.

Resonant circuits
 
Two important elements are the coil and the capacitor, particularly if they appear together as resonant circuit. The calculation determine mutually the frequency, the inductivity and the capacity of a tank circuit.

Matches with LC networks
 
Two circuit groups with different resistances can be connected with less loss over a coil and a capacitor. The values of the LC networks determined with the calculation of match of resistances are valid always only for one frequency, since the used parts are frequency-dependent.
But it is not necessary, lest the output resistor is a resistance. It can be also a reactance. The script calculate only LC networks with low-pass characteristic. Such LC networks are in use in antenna tuners. The values of the LC networks determined with the calculation of match of reactances are valid always only for one frequency, since the used parts are frequency-dependent.