[Lf] LF: PSK31 generation]

[Andre Kesteloot]

Johan Bodin wrote:

> Dear Jim and the Group
>
> Jim Moritz wrote:
>
> > I tried some experiments with a scheme similar to that suggested by Johan -
> > The problem with this is that, while the square wave output contains
> > essentially no even harmonics, as soon as you change the duty cycle, or the
> > relative phase of the two totem pole outputs, a strong second harmonic
> > component appears.
>
> I don't understand this... Perhaps I am missing something, but as far as I can see,
> the waveform *will* be symmetrical if the drive to each totem pole has a 50/50 duty
> cycle and the modulation is done only by varying the phase between the totem pole
> drivers 0 - 180 degrees. For example, with 90 degrees shift it looks like this:
>
> 0, +1, 0, -1, 0, +1, 0, -1...
>
> Curiousity made me write a simple program to simulate the signal. The program
> generated an audio file containing the difference between two 50/50 square waves.
> It starts with the two waves at 180 degrees. The phase difference is then gradually
> reduced to zero at the end of the file.
>
> The file was analysed whith Spectrogram - there was no sign of any even harmonic!
>
> (This was easier than doing Fourier calculations :-)
>
> As expected, the level of 3*F approaches that of 1*F when the phase shift
> approaches zero.
>
> As Andy mentioned, the fundamental voltage / phase ratio seems *very*
> non-linear.
>
> 73
> Johan SM6LKM