Centre tapped transformers - input and output

[brett]

Hi
I've got myself confused about centre-tapped transformers.

For simplicity, let's assume that we a coupling transformer with 100 centre-tapped turns on the primary and 100 turns on the secondary. 
If we feed the positive part of an input signal to one end of the primary and the negative part to the other end, what is the amplitude of the signal in the secondary?

Is the output equal to the input signal, because the overall turns ratio is 100:100 ?
Or is it double the the input signal because the turns used are 50:100 for the positive part of the signal, and 50:100 for the positive part?

I know that I should know this, but I know that I don't. 
thanks

[R.G.]

A signal impressed on a transformer winding causes a constant volts per turn to be set up on any turns in the transformer. Period.

So if you feed 100 turns and take it out on some other 100 turns, the voltage is nominally equal.

For the example you give, you feed a signal to 100 turns and take it out on 100 turns. The center tap is not connected, so it may as well not exist. The signal will be the same - minus losses in the wire, capacitance and core of a few percent.

[brett]

Thanks RG.