Harry Dalek wrote: ,and i recall Klaas and he's P7 SSTV he built in the 70s recased and finished 2 or 3 years back so don't worry to much about the time every one does the same when you feel like it you work on it to your time table .
Klaas Robers wrote:...And then suddenly there pops up a new project, that looks much more attractive than finishing the current projects .....
Klaas Robers » Tue Jun 21, 2016 4:18 pm
Steve, it is already for quite some time that I wonder if an FM demodulator or discriminator shouldn't have an S-curve that is linear over the whole bandwidth of the FM spectrum. That is for SSTV it should be straight from 300 Hz (1200 - 900) up to 3200 Hz (2300 + 900). For the lower limit it could be 600 Hz (1500-900) because I allow the demodulated sync pulses to be distorted, as the sync is extracted in a different way.
Although, one might think that the frequency never goes lower than 1200 Hz (1500 for the video content) and higher than 2300 Hz. But the side bands are not in the signal just for fun. If you demodulate the FM with two tuned circuits, one at 1200 Hz and one on 2300 Hz, as ROBOT did, then you mis the side bands between 2300 and 3200 Hz, isn't it? At least they are attenuated in stead of boosted.
If I watch in this thread the page 10 then I see that for your demodulated "Blokgolf" signal, that in the upgoing black to white transients there is no ringing of the low pass filter, but a somewhat rounded shoulder, while at the white to black transients there is ringing and it looks as if the transients are steeper. In the same page a photo of an oscilloscope screen shows ringing up as well as down from a grey scale signal.
However, video signals are strange things. A picture has other requirements than audio.
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