RE: Is this correct?

[Allen.Windhorn]

> -----Original Message-----
> From: address@hidden
> 
> When I changed the dt=1/100/fc to get finer resolution it became
> obvious that going up using my original version, the final
> 'frequency was indeed 500MHz and going down the final frequency was
> indeed 200MHz. so the fft's were both correct, it was my 'time'
> waveform checks that were wrong!
> 
> I had checked that time looked right, but the resolution was so
> poor, didn't notice that the frequency did go up to 500MHz! Thanks!
> 
> To correct for this, I had originally thrown in the divide by two,
> but did not understand the 'why'

The "why" I think is that you are changing the frequency starting at
the beginning of the sweep.  This sounds confusing...what I mean is
for every frequency step you start with zero phase at zero time, so
you have a multiplier effect by the time you get to wherever you are
in the sweep.  So effectively the sweep rate speeds up with time.
If you saved the phase angle every step and started at that phase
angle for the next step you would be OK.  It's like a folding drying
rack where if you move the first rung a bit the end zooms out.
Hope this is helpful but I doubt it :-)

Allen