Q:

FSK generation with Timer 555

On the Internet I found FSK generator connection diagram. And I'm trying to connect up it in Qucs.
I' sure, 555 timer is working properly. But at the output of the whole schema I get unclear result.
P.S. Output.Vt does not depend on the input bit stream.
Look, please, what could be wrong?

A:

If you look at the left side of the original circuit you will see that the input data rate is expected to be 150 Hz, and the output frequency then switches between 1070 Hz and 1270 Hz.
Your input signal is 100 MHz, much too fast for this circuit. To perform FSK with an input frequency of 100 MHz you will need an oscillator with a nominal frequency of 1 GHz or so...and a 555 timer will never achieve that.

