How to combine two signals?

[DimaA]

combine two dc voltages

It may be a dumb question, but how do I combine two signals together? I have a sine wave, and a DC voltage, I want to combine them so the sine wave will "ride" on DC votage.

 

[IanP]

This can be done using two components at each end:
- to deliver dc to a line you have to use an inductor; identical inductor you will use at the other end ..
- to send sine wave over the same cable you will use a capacitor .. and at the other end you will pick up the sine wave again using a capacitor ..

To calculate values of inductor and capacitor use common formulas:
RL = ωL
RC = 1/ωC
and the values should be in the range of 1kΩ or more for L and ≤10Ω for C .. use the minimum sine wave frequency you want to superimpose ..

 

[Moss]

In my opinion, best and more practical way is to use summing amplifier. It is a just operational amplifier with 3-4 resistors Look here **broken link removed** or search google.
You must select suitable OP depending on your voltages & frquencies.